summaryrefslogtreecommitdiff
path: root/doc/lispref/windows.texi
blob: 9ddd69ab7e76fa77fbb2834dfd523886c0478714 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
4342
4343
4344
4345
4346
4347
4348
4349
4350
4351
4352
4353
4354
4355
4356
4357
4358
4359
4360
4361
4362
4363
4364
4365
4366
4367
4368
4369
4370
4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387
4388
4389
4390
4391
4392
4393
4394
4395
4396
4397
4398
4399
4400
4401
4402
4403
4404
4405
4406
4407
4408
4409
4410
4411
4412
4413
4414
4415
4416
4417
4418
4419
4420
4421
4422
4423
4424
4425
4426
4427
4428
4429
4430
4431
4432
4433
4434
4435
4436
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
4544
4545
4546
4547
4548
4549
4550
4551
4552
4553
4554
4555
4556
4557
4558
4559
4560
4561
4562
4563
4564
4565
4566
4567
4568
4569
4570
4571
4572
4573
4574
4575
4576
4577
4578
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
4595
4596
4597
4598
4599
4600
4601
4602
4603
4604
4605
4606
4607
4608
4609
4610
4611
4612
4613
4614
4615
4616
4617
4618
4619
4620
4621
4622
4623
4624
4625
4626
4627
4628
4629
4630
4631
4632
4633
4634
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
4646
4647
4648
4649
4650
4651
4652
4653
4654
4655
4656
4657
4658
4659
4660
4661
4662
4663
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
4677
4678
4679
4680
4681
4682
4683
4684
4685
4686
4687
4688
4689
4690
4691
4692
4693
4694
4695
4696
4697
4698
4699
4700
4701
4702
4703
4704
4705
4706
4707
4708
4709
4710
4711
4712
4713
4714
4715
4716
4717
4718
4719
4720
4721
4722
4723
4724
4725
4726
4727
4728
4729
4730
4731
4732
4733
4734
4735
4736
4737
4738
4739
4740
4741
4742
4743
4744
4745
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757
4758
4759
4760
4761
4762
4763
4764
4765
4766
4767
4768
4769
4770
4771
4772
4773
4774
4775
4776
4777
4778
4779
4780
4781
4782
4783
4784
4785
4786
4787
4788
4789
4790
4791
4792
4793
4794
4795
4796
4797
4798
4799
4800
4801
4802
4803
4804
4805
4806
4807
4808
4809
4810
4811
4812
4813
4814
4815
4816
4817
4818
4819
4820
4821
4822
4823
4824
4825
4826
4827
4828
4829
4830
4831
4832
4833
4834
4835
4836
4837
4838
4839
4840
4841
4842
4843
4844
4845
4846
4847
4848
4849
4850
4851
4852
4853
4854
4855
4856
4857
4858
4859
4860
4861
4862
4863
4864
4865
4866
4867
4868
4869
4870
4871
4872
4873
4874
4875
4876
4877
4878
4879
4880
4881
4882
4883
4884
4885
4886
4887
4888
4889
4890
4891
4892
4893
4894
4895
4896
4897
4898
4899
4900
4901
4902
4903
4904
4905
4906
4907
4908
4909
4910
4911
4912
4913
4914
4915
4916
4917
4918
4919
4920
4921
4922
4923
4924
4925
4926
4927
4928
4929
4930
4931
4932
4933
4934
4935
4936
4937
4938
4939
4940
4941
4942
4943
4944
4945
4946
4947
4948
4949
4950
4951
4952
4953
4954
4955
4956
4957
4958
4959
4960
4961
4962
4963
4964
4965
4966
4967
4968
4969
4970
4971
4972
4973
4974
4975
4976
4977
4978
4979
4980
4981
4982
4983
4984
4985
4986
4987
4988
4989
4990
4991
4992
4993
4994
4995
4996
4997
4998
4999
5000
5001
5002
5003
5004
5005
5006
5007
5008
5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020
5021
5022
5023
5024
5025
5026
5027
5028
5029
5030
5031
5032
5033
5034
5035
5036
5037
5038
5039
5040
5041
5042
5043
5044
5045
5046
5047
5048
5049
5050
5051
5052
5053
5054
5055
5056
5057
5058
5059
5060
5061
5062
5063
5064
5065
5066
5067
5068
5069
5070
5071
5072
5073
5074
5075
5076
5077
5078
5079
5080
5081
5082
5083
5084
5085
5086
5087
5088
5089
5090
5091
5092
5093
5094
5095
5096
5097
5098
5099
5100
5101
5102
5103
5104
5105
5106
5107
5108
5109
5110
5111
5112
5113
5114
5115
5116
5117
5118
5119
5120
5121
5122
5123
5124
5125
5126
5127
5128
5129
5130
5131
5132
5133
5134
5135
5136
5137
5138
5139
5140
5141
5142
5143
5144
5145
5146
5147
5148
5149
5150
5151
5152
5153
5154
5155
5156
5157
5158
5159
5160
5161
5162
5163
5164
5165
5166
5167
5168
5169
5170
5171
5172
5173
5174
5175
5176
5177
5178
5179
5180
5181
5182
5183
5184
5185
5186
5187
5188
5189
5190
5191
5192
5193
5194
5195
5196
5197
5198
5199
5200
5201
5202
5203
5204
5205
5206
5207
5208
5209
5210
5211
5212
5213
5214
5215
5216
5217
5218
5219
5220
5221
5222
5223
5224
5225
5226
5227
5228
5229
5230
5231
5232
5233
5234
5235
5236
5237
5238
5239
5240
5241
5242
5243
5244
5245
5246
5247
5248
5249
5250
5251
5252
5253
5254
5255
5256
5257
5258
5259
5260
5261
5262
5263
5264
5265
5266
5267
5268
5269
5270
5271
5272
5273
5274
5275
5276
5277
5278
5279
5280
5281
5282
5283
5284
5285
5286
5287
5288
5289
5290
5291
5292
5293
5294
5295
5296
5297
5298
5299
5300
5301
5302
5303
5304
5305
5306
5307
5308
5309
5310
5311
5312
5313
5314
5315
5316
5317
5318
5319
5320
5321
5322
5323
5324
5325
5326
5327
5328
5329
5330
5331
5332
5333
5334
5335
5336
5337
5338
5339
5340
5341
5342
5343
5344
5345
5346
5347
5348
5349
5350
5351
5352
5353
5354
5355
5356
5357
5358
5359
5360
5361
5362
5363
5364
5365
5366
5367
5368
5369
5370
5371
5372
5373
5374
5375
5376
5377
5378
5379
5380
5381
5382
5383
5384
5385
5386
5387
5388
5389
5390
5391
5392
5393
5394
5395
5396
5397
5398
5399
5400
5401
5402
5403
5404
5405
5406
5407
5408
5409
5410
5411
5412
5413
5414
5415
5416
5417
5418
5419
5420
5421
5422
5423
5424
5425
5426
5427
5428
5429
5430
5431
5432
5433
5434
5435
5436
5437
5438
5439
5440
5441
5442
5443
5444
5445
5446
5447
5448
5449
5450
5451
5452
5453
5454
5455
5456
5457
5458
5459
5460
5461
5462
5463
5464
5465
5466
5467
5468
5469
5470
5471
5472
5473
5474
5475
5476
5477
5478
5479
5480
5481
5482
5483
5484
5485
5486
5487
5488
5489
5490
5491
5492
5493
5494
5495
5496
5497
5498
5499
5500
5501
5502
5503
5504
5505
5506
5507
5508
5509
5510
5511
5512
5513
5514
5515
5516
5517
5518
5519
5520
5521
5522
5523
5524
5525
5526
5527
5528
5529
5530
5531
5532
5533
5534
5535
5536
5537
5538
5539
5540
5541
5542
5543
5544
5545
5546
5547
5548
5549
5550
5551
5552
5553
5554
5555
5556
5557
5558
5559
5560
5561
5562
5563
5564
5565
5566
5567
5568
5569
5570
5571
5572
5573
5574
5575
5576
5577
5578
5579
5580
5581
5582
5583
5584
5585
5586
5587
5588
5589
5590
5591
5592
5593
5594
5595
5596
5597
5598
5599
5600
5601
5602
5603
5604
5605
5606
5607
5608
5609
5610
5611
5612
5613
5614
5615
5616
5617
5618
5619
5620
5621
5622
5623
5624
5625
5626
5627
5628
5629
5630
5631
5632
5633
5634
5635
5636
5637
5638
5639
5640
5641
5642
5643
5644
5645
5646
5647
5648
5649
5650
5651
5652
5653
5654
5655
5656
5657
5658
5659
5660
5661
5662
5663
5664
5665
5666
5667
5668
5669
5670
5671
5672
5673
5674
5675
5676
5677
5678
5679
5680
5681
5682
5683
5684
5685
5686
5687
5688
5689
5690
5691
5692
5693
5694
5695
5696
5697
5698
5699
5700
5701
5702
5703
5704
5705
5706
5707
5708
5709
5710
5711
5712
5713
5714
5715
5716
5717
5718
5719
5720
5721
5722
5723
5724
5725
5726
5727
5728
5729
5730
5731
5732
5733
5734
5735
5736
5737
5738
5739
5740
5741
5742
5743
5744
5745
5746
5747
5748
5749
5750
5751
5752
5753
5754
5755
5756
5757
5758
5759
5760
5761
5762
5763
5764
5765
5766
5767
5768
5769
5770
5771
5772
5773
5774
5775
5776
5777
5778
5779
5780
5781
5782
5783
5784
5785
5786
5787
5788
5789
5790
5791
5792
5793
5794
5795
5796
5797
5798
5799
5800
5801
5802
5803
5804
5805
5806
5807
5808
5809
5810
5811
5812
5813
5814
5815
5816
5817
5818
5819
5820
5821
5822
5823
5824
5825
5826
5827
5828
5829
5830
5831
5832
5833
5834
5835
5836
5837
5838
5839
5840
5841
5842
5843
5844
5845
5846
5847
5848
5849
5850
5851
5852
5853
5854
5855
5856
5857
5858
5859
5860
5861
5862
5863
5864
5865
5866
5867
5868
5869
5870
5871
5872
5873
5874
5875
5876
5877
5878
5879
5880
5881
5882
5883
5884
5885
5886
5887
5888
5889
5890
5891
5892
5893
5894
5895
5896
5897
5898
5899
5900
5901
5902
5903
5904
5905
5906
5907
5908
5909
5910
5911
5912
5913
5914
5915
5916
5917
5918
5919
5920
5921
5922
5923
5924
5925
5926
5927
5928
5929
5930
5931
5932
5933
5934
5935
5936
5937
5938
5939
5940
5941
5942
5943
5944
5945
5946
5947
5948
5949
5950
5951
5952
5953
5954
5955
5956
5957
5958
5959
5960
5961
5962
5963
5964
5965
5966
5967
5968
5969
5970
5971
5972
5973
5974
5975
5976
5977
5978
5979
5980
5981
5982
5983
5984
5985
5986
5987
5988
5989
5990
5991
5992
5993
5994
5995
5996
5997
5998
5999
6000
6001
6002
6003
6004
6005
6006
6007
6008
6009
6010
6011
6012
6013
6014
6015
6016
6017
6018
6019
6020
6021
6022
6023
6024
6025
6026
6027
6028
6029
6030
6031
6032
6033
6034
6035
6036
6037
6038
6039
6040
6041
6042
6043
6044
6045
6046
6047
6048
6049
6050
6051
6052
6053
6054
6055
6056
6057
6058
6059
6060
6061
6062
6063
6064
6065
6066
6067
6068
6069
6070
6071
6072
6073
6074
6075
6076
6077
6078
6079
6080
6081
6082
6083
6084
6085
6086
6087
6088
6089
6090
6091
6092
6093
6094
6095
6096
6097
6098
6099
6100
6101
6102
6103
6104
6105
6106
6107
6108
6109
6110
6111
6112
6113
6114
6115
6116
6117
6118
6119
6120
6121
6122
6123
6124
6125
6126
6127
6128
6129
6130
6131
6132
6133
6134
6135
6136
6137
6138
6139
6140
6141
6142
6143
6144
6145
6146
6147
6148
6149
6150
6151
6152
6153
6154
6155
6156
6157
6158
6159
6160
6161
6162
6163
6164
6165
6166
6167
6168
6169
6170
6171
6172
6173
6174
6175
6176
6177
6178
6179
6180
6181
6182
6183
6184
6185
6186
6187
6188
6189
6190
6191
6192
6193
6194
6195
6196
6197
6198
6199
6200
6201
6202
6203
6204
6205
6206
6207
6208
6209
6210
6211
6212
6213
6214
6215
6216
6217
6218
6219
6220
6221
6222
6223
6224
6225
6226
6227
6228
6229
6230
6231
6232
6233
6234
6235
6236
6237
6238
6239
6240
6241
6242
6243
6244
6245
6246
6247
6248
6249
6250
6251
6252
6253
6254
6255
6256
6257
6258
6259
6260
6261
6262
6263
6264
6265
6266
6267
6268
6269
6270
6271
6272
6273
6274
6275
6276
6277
6278
6279
6280
6281
6282
6283
6284
6285
6286
6287
6288
6289
6290
6291
6292
6293
6294
6295
6296
6297
6298
6299
6300
6301
6302
6303
6304
6305
6306
6307
6308
6309
6310
6311
6312
6313
6314
6315
6316
6317
6318
6319
6320
6321
6322
6323
6324
6325
6326
6327
6328
6329
6330
6331
6332
6333
6334
6335
6336
6337
6338
6339
6340
6341
6342
6343
6344
6345
6346
6347
6348
6349
6350
6351
6352
6353
6354
6355
6356
6357
6358
6359
6360
6361
6362
6363
6364
6365
6366
6367
6368
6369
6370
6371
6372
6373
6374
6375
6376
6377
6378
6379
6380
6381
6382
6383
6384
6385
6386
6387
6388
6389
6390
6391
6392
6393
6394
6395
6396
6397
6398
6399
6400
6401
6402
6403
6404
6405
6406
6407
6408
6409
6410
6411
6412
6413
6414
6415
6416
6417
6418
6419
6420
6421
6422
6423
6424
6425
6426
6427
6428
6429
6430
6431
6432
6433
6434
6435
6436
6437
6438
6439
6440
6441
6442
6443
6444
6445
6446
6447
6448
6449
6450
6451
6452
6453
6454
6455
6456
6457
6458
6459
6460
6461
6462
6463
6464
6465
6466
6467
6468
6469
6470
6471
6472
6473
6474
6475
6476
6477
6478
6479
6480
6481
6482
6483
6484
6485
6486
6487
6488
6489
6490
6491
6492
6493
6494
6495
6496
6497
6498
6499
6500
6501
6502
6503
6504
6505
6506
6507
6508
6509
6510
6511
6512
6513
6514
6515
6516
6517
6518
6519
6520
6521
6522
6523
6524
@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990-1995, 1998-1999, 2001-2019 Free Software
@c Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@node Windows
@chapter Windows

This chapter describes the functions and variables related to Emacs
windows.  @xref{Frames}, for how windows are assigned an area of screen
available for Emacs to use.  @xref{Display}, for information on how text
is displayed in windows.

@menu
* Basic Windows::           Basic information on using windows.
* Windows and Frames::      Relating windows to the frame they appear on.
* Window Sizes::            Accessing a window's size.
* Resizing Windows::        Changing the sizes of windows.
* Preserving Window Sizes:: Preserving the size of windows.
* Splitting Windows::       Creating a new window.
* Deleting Windows::        Removing a window from its frame.
* Recombining Windows::     Preserving the frame layout when splitting and
                              deleting windows.
* Selecting Windows::       The selected window is the one that you edit in.
* Cyclic Window Ordering::  Moving around the existing windows.
* Buffers and Windows::     Each window displays the contents of a buffer.
* Switching Buffers::       Higher-level functions for switching to a buffer.
* Displaying Buffers::      Displaying a buffer in a suitable window.
* Window History::          Each window remembers the buffers displayed in it.
* Dedicated Windows::       How to avoid displaying another buffer in
                              a specific window.
* Quitting Windows::        How to restore the state prior to displaying a
                              buffer.
* Side Windows::            Special windows on a frame's sides.
* Atomic Windows::          Preserving parts of the window layout.
* Window Point::            Each window has its own location of point.
* Window Start and End::    Buffer positions indicating which text is
                              on-screen in a window.
* Textual Scrolling::       Moving text up and down through the window.
* Vertical Scrolling::      Moving the contents up and down on the window.
* Horizontal Scrolling::    Moving the contents sideways on the window.
* Coordinates and Windows:: Converting coordinates to windows.
* Mouse Window Auto-selection:: Automatically selecting windows with the mouse.
* Window Configurations::   Saving and restoring the state of the screen.
* Window Parameters::       Associating additional information with windows.
* Window Hooks::            Hooks for scrolling, window size changes,
                              redisplay going past a certain point,
                              or window configuration changes.
@end menu


@node Basic Windows
@section Basic Concepts of Emacs Windows
@cindex window

A @dfn{window} is an area of the screen that is used to display a buffer
(@pxref{Buffers}).  In Emacs Lisp, windows are represented by a special
Lisp object type.

@cindex multiple windows
  Windows are grouped into frames (@pxref{Frames}).  Each frame
contains at least one window; the user can subdivide it into multiple,
non-overlapping windows to view several buffers at once.  Lisp
programs can use multiple windows for a variety of purposes.  In
Rmail, for example, you can view a summary of message titles in one
window, and the contents of the selected message in another window.

@cindex terminal screen
@cindex screen of terminal
  Emacs uses the word ``window'' with a different meaning than in
graphical desktop environments and window systems, such as the X
Window System.  When Emacs is run on X, each of its graphical X
windows is an Emacs frame (containing one or more Emacs windows).
When Emacs is run on a text terminal, the frame fills the entire
terminal screen.

@cindex tiled windows
  Unlike X windows, Emacs windows are @dfn{tiled}; they never overlap
within the area of the frame.  When a window is created, resized, or
deleted, the change in window space is taken from or given to the
adjacent windows, so that the total area of the frame is unchanged.

@defun windowp object
This function returns @code{t} if @var{object} is a window (whether or
not it displays a buffer).  Otherwise, it returns @code{nil}.
@end defun

@cindex live windows
A @dfn{live window} is one that is actually displaying a buffer in a
frame.

@defun window-live-p object
This function returns @code{t} if @var{object} is a live window and
@code{nil} otherwise.  A live window is one that displays a buffer.
@end defun

@cindex internal windows
The windows in each frame are organized into a @dfn{window tree}.
@xref{Windows and Frames}.  The leaf nodes of each window tree are live
windows---the ones actually displaying buffers.  The internal nodes of
the window tree are @dfn{internal windows}, which are not live.

@cindex valid windows
   A @dfn{valid window} is one that is either live or internal.  A valid
window can be @dfn{deleted}, i.e., removed from its frame
(@pxref{Deleting Windows}); then it is no longer valid, but the Lisp
object representing it might be still referenced from other Lisp
objects.  A deleted window may be made valid again by restoring a saved
window configuration (@pxref{Window Configurations}).

   You can distinguish valid windows from deleted windows with
@code{window-valid-p}.

@defun window-valid-p object
This function returns @code{t} if @var{object} is a live window, or an
internal window in a window tree.  Otherwise, it returns @code{nil},
including for the case where @var{object} is a deleted window.
@end defun

@cindex selected window
@cindex window selected within a frame
  In each frame, at any time, exactly one Emacs window is designated
as @dfn{selected within the frame}.  For the selected frame, that
window is called the @dfn{selected window}---the one in which most
editing takes place, and in which the cursor for selected windows
appears (@pxref{Cursor Parameters}).  Keyboard input that inserts or
deletes text is also normally directed to this window.   The selected
window's buffer is usually also the current buffer, except when
@code{set-buffer} has been used (@pxref{Current Buffer}).  As for
non-selected frames, the window selected within the frame becomes the
selected window if the frame is ever selected.  @xref{Selecting
Windows}.

@defun selected-window
This function returns the selected window (which is always a live
window).
@end defun

@anchor{Window Group}Sometimes several windows collectively and
cooperatively display a buffer, for example, under the management of
Follow Mode (@pxref{Follow Mode,,, emacs}), where the windows together
display a bigger portion of the buffer than one window could alone.
It is often useful to consider such a @dfn{window group} as a single
entity.  Several functions such as @code{window-group-start}
(@pxref{Window Start and End}) allow you to do this by supplying, as
an argument, one of the windows as a stand in for the whole group.

@defun selected-window-group
@vindex selected-window-group-function
When the selected window is a member of a group of windows, this
function returns a list of the windows in the group, ordered such that
the first window in the list is displaying the earliest part of the
buffer, and so on.  Otherwise the function returns a list containing
just the selected window.

The selected window is considered part of a group when the buffer
local variable @code{selected-window-group-function} is set to a
function.  In this case, @code{selected-window-group} calls it with no
arguments and returns its result (which should be the list of windows
in the group).
@end defun

@node Windows and Frames
@section Windows and Frames

Each window belongs to exactly one frame (@pxref{Frames}).

@defun window-frame &optional window
This function returns the frame that the window @var{window} belongs
to.  If @var{window} is @code{nil}, it defaults to the selected
window.
@end defun

@defun window-list &optional frame minibuffer window
This function returns a list of live windows belonging to the frame
@var{frame}.  If @var{frame} is omitted or @code{nil}, it defaults to
the selected frame.

The optional argument @var{minibuffer} specifies whether to include
the minibuffer window in the returned list.  If @var{minibuffer} is
@code{t}, the minibuffer window is included.  If @var{minibuffer} is
@code{nil} or omitted, the minibuffer window is included only if it is
active.  If @var{minibuffer} is neither @code{nil} nor @code{t}, the
minibuffer window is never included.

The optional argument @var{window}, if non-@code{nil}, should be a live
window on the specified frame; then @var{window} will be the first
element in the returned list.  If @var{window} is omitted or @code{nil},
the window selected within the frame is the first element.
@end defun

@cindex window tree
@cindex root window
  Windows in the same frame are organized into a @dfn{window tree},
whose leaf nodes are the live windows.  The internal nodes of a window
tree are not live; they exist for the purpose of organizing the
relationships between live windows.  The root node of a window tree is
called the @dfn{root window}.  It can be either a live window (if the
frame has just one window), or an internal window.

  A minibuffer window (@pxref{Minibuffer Windows}) that is not alone
on its frame does not have a parent window, so it strictly speaking is
not part of its frame's window tree.  Nonetheless, it is a sibling
window of the frame's root window, and thus can be reached via
@code{window-next-sibling}.  Also, the function @code{window-tree}
described at the end of this section lists the minibuffer window
alongside the actual window tree.

@defun frame-root-window &optional frame-or-window
This function returns the root window for @var{frame-or-window}.  The
argument @var{frame-or-window} should be either a window or a frame;
if omitted or @code{nil}, it defaults to the selected frame.  If
@var{frame-or-window} is a window, the return value is the root window
of that window's frame.
@end defun

@cindex parent window
@cindex child window
@cindex sibling window
  When a window is split, there are two live windows where previously
there was one.  One of these is represented by the same Lisp window
object as the original window, and the other is represented by a
newly-created Lisp window object.  Both of these live windows become
leaf nodes of the window tree, as @dfn{child windows} of a single
internal window.  If necessary, Emacs automatically creates this
internal window, which is also called the @dfn{parent window}, and
assigns it to the appropriate position in the window tree.  A set of
windows that share the same parent are called @dfn{siblings}.

@cindex parent window
@defun window-parent &optional window
This function returns the parent window of @var{window}.  If
@var{window} is omitted or @code{nil}, it defaults to the selected
window.  The return value is @code{nil} if @var{window} has no parent
(i.e., it is a minibuffer window or the root window of its frame).
@end defun

  Each internal window always has at least two child windows.  If this
number falls to one as a result of window deletion, Emacs
automatically deletes the internal window, and its sole remaining
child window takes its place in the window tree.

  Each child window can be either a live window, or an internal window
(which in turn would have its own child windows).  Therefore, each
internal window can be thought of as occupying a certain rectangular
@dfn{screen area}---the union of the areas occupied by the live
windows that are ultimately descended from it.

@cindex window combination
@cindex vertical combination
@cindex horizontal combination
  For each internal window, the screen areas of the immediate children
are arranged either vertically or horizontally (never both).  If the
child windows are arranged one above the other, they are said to form
a @dfn{vertical combination}; if they are arranged side by side, they
are said to form a @dfn{horizontal combination}.  Consider the
following example:

@smallexample
@group
     ______________________________________
    | ______  ____________________________ |
    ||      || __________________________ ||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||____________W4____________|||
    ||      || __________________________ ||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||____________W5____________|||
    ||__W2__||_____________W3_____________ |
    |__________________W1__________________|

@end group
@end smallexample

@noindent
The root window of this frame is an internal window, @var{W1}.  Its
child windows form a horizontal combination, consisting of the live
window @var{W2} and the internal window @var{W3}.  The child windows
of @var{W3} form a vertical combination, consisting of the live
windows @var{W4} and @var{W5}.  Hence, the live windows in this
window tree are @var{W2}, @var{W4}, and @var{W5}.

  The following functions can be used to retrieve a child window of an
internal window, and the siblings of a child window.

@defun window-top-child &optional window
This function returns the topmost child window of @var{window}, if
@var{window} is an internal window whose children form a vertical
combination.  For any other type of window, the return value is
@code{nil}.
@end defun

@defun window-left-child &optional window
This function returns the leftmost child window of @var{window}, if
@var{window} is an internal window whose children form a horizontal
combination.  For any other type of window, the return value is
@code{nil}.
@end defun

@defun window-child window
This function returns the first child window of the internal window
@var{window}---the topmost child window for a vertical combination, or
the leftmost child window for a horizontal combination.  If
@var{window} is a live window, the return value is @code{nil}.
@end defun

@defun window-combined-p &optional window horizontal
This function returns a non-@code{nil} value if and only if
@var{window} is part of a vertical combination.  If @var{window} is
omitted or @code{nil}, it defaults to the selected one.

If the optional argument @var{horizontal} is non-@code{nil}, this
means to return non-@code{nil} if and only if @var{window} is part of
a horizontal combination.
@end defun

@defun window-next-sibling &optional window
This function returns the next sibling of the window @var{window}.  If
omitted or @code{nil}, @var{window} defaults to the selected window.
The return value is @code{nil} if @var{window} is the last child of
its parent.
@end defun

@defun window-prev-sibling &optional window
This function returns the previous sibling of the window @var{window}.
If omitted or @code{nil}, @var{window} defaults to the selected
window.  The return value is @code{nil} if @var{window} is the first
child of its parent.
@end defun

The functions @code{window-next-sibling} and
@code{window-prev-sibling} should not be confused with the functions
@code{next-window} and @code{previous-window}, which return the next
and previous window, respectively, in the cyclic ordering of windows
(@pxref{Cyclic Window Ordering}).

  The following functions can be useful to locate a window within its
frame.

@defun frame-first-window &optional frame-or-window
This function returns the live window at the upper left corner of the
frame specified by @var{frame-or-window}.  The argument
@var{frame-or-window} must denote a window or a live frame and defaults
to the selected frame.  If @var{frame-or-window} specifies a window,
this function returns the first window on that window's frame.  Under
the assumption that the frame from our canonical example is selected
@code{(frame-first-window)} returns @var{W2}.
@end defun

@defun window-at-side-p &optional window side
This function returns @code{t} if @var{window} is located at
@var{side} of its containing frame.  The argument @var{window} must be
a valid window and defaults to the selected one.  The argument
@var{side} can be any of the symbols @code{left}, @code{top},
@code{right} or @code{bottom}.  The default value @code{nil} is
handled like @code{bottom}.

Note that this function disregards the minibuffer window
(@pxref{Minibuffer Windows}).  Hence, with @var{side} equal to
@code{bottom} it may return @code{t} also when the minibuffer window
appears right below @var{window}.
@end defun

@cindex window in direction
@defun window-in-direction direction &optional window ignore sign wrap mini
This function returns the nearest live window in direction
@var{direction} as seen from the position of @code{window-point} in
window @var{window}.  The argument @var{direction} must be one of
@code{above}, @code{below}, @code{left} or @code{right}.  The optional
argument @var{window} must denote a live window and defaults to the
selected one.

This function does not return a window whose @code{no-other-window}
parameter is non-@code{nil} (@pxref{Window Parameters}).  If the nearest
window's @code{no-other-window} parameter is non-@code{nil}, this
function tries to find another window in the indicated direction whose
@code{no-other-window} parameter is @code{nil}.  If the optional
argument @var{ignore} is non-@code{nil}, a window may be returned even
if its @code{no-other-window} parameter is non-@code{nil}.

If the optional argument @var{sign} is a negative number, it means to
use the right or bottom edge of @var{window} as reference position
instead of @code{window-point}.  If @var{sign} is a positive number, it
means to use the left or top edge of @var{window} as reference position.

If the optional argument @var{wrap} is non-@code{nil}, this means to
wrap @var{direction} around frame borders.  For example, if @var{window}
is at the top of the frame and @var{direction} is @code{above}, then
this function usually returns the frame's minibuffer window if it's
active and a window at the bottom of the frame otherwise.

If the optional argument @var{mini} is @code{nil}, this means to return
the minibuffer window if and only if it is currently active.  If
@var{mini} is non-@code{nil}, this function may return the minibuffer
window even when it's not active.  However, if @var{wrap} is
non-@code{nil}, it always acts as if @var{mini} were @code{nil}.

If it doesn't find a suitable window, this function returns
@code{nil}.

Don't use this function to check whether there is @emph{no} window in
@var{direction}.  Calling @code{window-at-side-p} described above is a
much more efficient way to do that.
@end defun

The following function allows the entire window tree of a frame to be
retrieved:

@defun window-tree &optional frame
This function returns a list representing the window tree for frame
@var{frame}.  If @var{frame} is omitted or @code{nil}, it defaults to
the selected frame.

The return value is a list of the form @code{(@var{root} @var{mini})},
where @var{root} represents the window tree of the frame's root
window, and @var{mini} is the frame's minibuffer window.

If the root window is live, @var{root} is that window itself.
Otherwise, @var{root} is a list @code{(@var{dir} @var{edges} @var{w1}
@var{w2} ...)} where @var{dir} is @code{nil} for a horizontal
combination and @code{t} for a vertical combination, @var{edges} gives
the size and position of the combination, and the remaining elements
are the child windows.  Each child window may again be a window object
(for a live window) or a list with the same format as above (for an
internal window).  The @var{edges} element is a list @code{(@var{left}
@var{top} @var{right} @var{bottom})}, similar to the value returned by
@code{window-edges} (@pxref{Coordinates and Windows}).
@end defun


@node Window Sizes
@section Window Sizes
@cindex window size
@cindex size of window

  The following schematic shows the structure of a live window:

@smallexample
@group
        ____________________________________________
       |______________ Header Line ______________|RD| ^
     ^ |LS|LM|LF|                       |RF|RM|RS|  | |
     | |  |  |  |                       |  |  |  |  | |
Window |  |  |  |       Text Area       |  |  |  |  | Window
Body | |  |  |  |     (Window Body)     |  |  |  |  | Total
Height |  |  |  |                       |  |  |  |  | Height
     | |  |  |  |<- Window Body Width ->|  |  |  |  | |
     v |__|__|__|_______________________|__|__|__|  | |
       |_________ Horizontal Scroll Bar _________|  | |
       |_______________ Mode Line _______________|__| |
       |_____________ Bottom Divider _______________| v
        <---------- Window Total Width ------------>

@end group
@end smallexample

@cindex window body
@cindex text area of a window
@cindex body of a window
  At the center of the window is the @dfn{text area}, or @dfn{body},
where the buffer text is displayed.  The text area can be surrounded by
a series of optional areas.  On the left and right, from innermost to
outermost, these are the left and right fringes, denoted by LF and RF
(@pxref{Fringes}); the left and right margins, denoted by LM and RM in
the schematic (@pxref{Display Margins}); the left or right vertical
scroll bar, only one of which is present at any time, denoted by LS and
RS (@pxref{Scroll Bars}); and the right divider, denoted by RD
(@pxref{Window Dividers}).  At the top of the window is the header line
(@pxref{Header Lines}).  At the bottom of the window are the horizontal
scroll bar (@pxref{Scroll Bars}); the mode line (@pxref{Mode Line
Format}); and the bottom divider (@pxref{Window Dividers}).

  Emacs provides miscellaneous functions for finding the height and
width of a window.  The return value of many of these functions can be
specified either in units of pixels or in units of lines and columns.
On a graphical display, the latter actually correspond to the height and
width of a default character specified by the frame's default font
as returned by @code{frame-char-height} and @code{frame-char-width}
(@pxref{Frame Font}).  Thus, if a window is displaying text with a
different font or size, the reported line height and column width for
that window may differ from the actual number of text lines or columns
displayed within it.

@cindex window height
@cindex height of a window
@cindex total height of a window
  The @dfn{total height} of a window is the number of lines comprising
the window's body, the header line, the horizontal scroll bar, the mode
line and the bottom divider (if any).

@defun window-total-height &optional window round
This function returns the total height, in lines, of the window
@var{window}.  If @var{window} is omitted or @code{nil}, it defaults to
the selected window.  If @var{window} is an internal window, the return
value is the total height occupied by its descendant windows.

  If a window's pixel height is not an integral multiple of its frame's
default character height, the number of lines occupied by the window is
rounded internally.  This is done in a way such that, if the window is a
parent window, the sum of the total heights of all its child windows
internally equals the total height of their parent.  This means that
although two windows have the same pixel height, their internal total
heights may differ by one line.  This means also, that if window is
vertically combined and has a next sibling, the topmost row of that
sibling can be calculated as the sum of this window's topmost row and
total height (@pxref{Coordinates and Windows})

  If the optional argument @var{round} is @code{ceiling}, this
function returns the smallest integer larger than @var{window}'s pixel
height divided by the character height of its frame; if it is
@code{floor}, it returns the largest integer smaller than said value;
with any other @var{round} it returns the internal value of
@var{windows}'s total height.
@end defun

@cindex window width
@cindex width of a window
@cindex total width of a window
The @dfn{total width} of a window is the number of lines comprising the
window's body, its margins, fringes, scroll bars and a right divider (if
any).

@defun window-total-width &optional window round
This function returns the total width, in columns, of the window
@var{window}.  If @var{window} is omitted or @code{nil}, it defaults to
the selected window.  If @var{window} is internal, the return value is
the total width occupied by its descendant windows.

  If a window's pixel width is not an integral multiple of its frame's
character width, the number of lines occupied by the window is rounded
internally.  This is done in a way such that, if the window is a parent
window, the sum of the total widths of all its children internally
equals the total width of their parent.  This means that although two
windows have the same pixel width, their internal total widths may
differ by one column.  This means also, that if this window is
horizontally combined and has a next sibling, the leftmost column of
that sibling can be calculated as the sum of this window's leftmost
column and total width (@pxref{Coordinates and Windows}).  The optional
argument @var{round} behaves as it does for @code{window-total-height}.
@end defun

@defun window-total-size &optional window horizontal round
This function returns either the total height in lines or the total
width in columns of the window @var{window}.  If @var{horizontal} is
omitted or @code{nil}, this is equivalent to calling
@code{window-total-height} for @var{window}; otherwise it is equivalent
to calling @code{window-total-width} for @var{window}.  The optional
argument @var{round} behaves as it does for @code{window-total-height}.
@end defun

The following two functions can be used to return the total size of a
window in units of pixels.

@cindex window pixel height
@cindex pixel height of a window
@cindex total pixel height of a window

@defun window-pixel-height &optional window
This function returns the total height of window @var{window} in pixels.
@var{window} must be a valid window and defaults to the selected one.

The return value includes mode and header line, a horizontal scroll bar
and a bottom divider, if any.  If @var{window} is an internal window,
its pixel height is the pixel height of the screen areas spanned by its
children.
@end defun

@cindex window pixel width
@cindex pixel width of a window
@cindex total pixel width of a window

@defun window-pixel-width &optional window
This function returns the width of window @var{window} in pixels.
@var{window} must be a valid window and defaults to the selected one.

The return value includes the fringes and margins of @var{window} as
well as any vertical dividers or scroll bars belonging to @var{window}.
If @var{window} is an internal window, its pixel width is the width of
the screen areas spanned by its children.
@end defun

@cindex full-width window
@cindex full-height window
  The following functions can be used to determine whether a given
window has any adjacent windows.

@defun window-full-height-p &optional window
This function returns non-@code{nil} if @var{window} has no other window
above or below it in its frame.  More precisely, this means that the
total height of @var{window} equals the total height of the root window
on that frame.  The minibuffer window does not count in this regard.  If
@var{window} is omitted or @code{nil}, it defaults to the selected
window.
@end defun

@defun window-full-width-p &optional window
This function returns non-@code{nil} if @var{window} has no other
window to the left or right in its frame, i.e., its total width equals
that of the root window on that frame.  If @var{window} is omitted or
@code{nil}, it defaults to the selected window.
@end defun

@cindex window body height
@cindex body height of a window
The @dfn{body height} of a window is the height of its text area, which
does not include a mode or header line, a horizontal scroll bar, or a
bottom divider.

@defun window-body-height &optional window pixelwise
This function returns the height, in lines, of the body of window
@var{window}.  If @var{window} is omitted or @code{nil}, it defaults to
the selected window; otherwise it must be a live window.

If the optional argument @var{pixelwise} is non-@code{nil}, this
function returns the body height of @var{window} counted in pixels.

If @var{pixelwise} is @code{nil}, the return value is rounded down to
the nearest integer, if necessary.  This means that if a line at the
bottom of the text area is only partially visible, that line is not
counted.  It also means that the height of a window's body can never
exceed its total height as returned by @code{window-total-height}.
@end defun

@cindex window body width
@cindex body width of a window
The @dfn{body width} of a window is the width of its text area, which
does not include the scroll bar, fringes, margins or a right divider.
Note that when one or both fringes are removed (by setting their width
to zero), the display engine reserves two character cells, one on each
side of the window, for displaying the continuation and truncation
glyphs, which leaves 2 columns less for text display.  (The function
@code{window-max-chars-per-line}, described below, takes this
peculiarity into account.)

@defun window-body-width &optional window pixelwise
This function returns the width, in columns, of the body of window
@var{window}.  If @var{window} is omitted or @code{nil}, it defaults to
the selected window; otherwise it must be a live window.

If the optional argument @var{pixelwise} is non-@code{nil}, this
function returns the body width of @var{window} in units of pixels.

If @var{pixelwise} is @code{nil}, the return value is rounded down to
the nearest integer, if necessary.  This means that if a column on the
right of the text area is only partially visible, that column is not
counted.  It also means that the width of a window's body can never
exceed its total width as returned by @code{window-total-width}.
@end defun

@cindex window body size
@cindex body size of a window
@defun window-body-size &optional window horizontal pixelwise
This function returns the body height or body width of @var{window}.  If
@var{horizontal} is omitted or @code{nil}, it is equivalent to calling
@code{window-body-height} for @var{window}; otherwise it is equivalent
to calling @code{window-body-width}.  In either case, the optional
argument @var{pixelwise} is passed to the function called.
@end defun

For compatibility with previous versions of Emacs,
@code{window-height} is an alias for @code{window-total-height}, and
@code{window-width} is an alias for @code{window-body-width}.  These
aliases are considered obsolete and will be removed in the future.

   The pixel heights of a window's mode and header line can be retrieved
with the functions given below.  Their return value is usually accurate
unless the window has not been displayed before: In that case, the
return value is based on an estimate of the font used for the window's
frame.

@defun window-mode-line-height &optional window
This function returns the height in pixels of @var{window}'s mode line.
@var{window} must be a live window and defaults to the selected one.  If
@var{window} has no mode line, the return value is zero.
@end defun

@defun window-header-line-height &optional window
This function returns the height in pixels of @var{window}'s header
line.  @var{window} must be a live window and defaults to the selected
one.  If @var{window} has no header line, the return value is zero.
@end defun

Functions for retrieving the height and/or width of window dividers
(@pxref{Window Dividers}), fringes (@pxref{Fringes}), scroll bars
(@pxref{Scroll Bars}), and display margins (@pxref{Display Margins}) are
described in the corresponding sections.

If your Lisp program needs to make layout decisions, you will find the
following function useful:

@defun window-max-chars-per-line &optional window face
This function returns the number of characters displayed in the
specified face @var{face} in the specified window @var{window} (which
must be a live window).  If @var{face} was remapped (@pxref{Face
Remapping}), the information is returned for the remapped face.  If
omitted or @code{nil}, @var{face} defaults to the default face, and
@var{window} defaults to the selected window.

Unlike @code{window-body-width}, this function accounts for the actual
size of @var{face}'s font, instead of working in units of the canonical
character width of @var{window}'s frame (@pxref{Frame Font}).  It also
accounts for space used by the continuation glyph, if @var{window} lacks
one or both of its fringes.
@end defun

@cindex fixed-size window
@vindex window-min-height
@vindex window-min-width
  Commands that change the size of windows (@pxref{Resizing Windows}),
or split them (@pxref{Splitting Windows}), obey the variables
@code{window-min-height} and @code{window-min-width}, which specify the
smallest allowable window height and width.  They also obey the variable
@code{window-size-fixed}, with which a window can be @dfn{fixed} in
size (@pxref{Preserving Window Sizes}).

@defopt window-min-height
This option specifies the minimum total height, in lines, of any window.
Its value has to accommodate at least one text line as well as a mode
and header line, a horizontal scroll bar and a bottom divider, if
present.
@end defopt

@defopt window-min-width
This option specifies the minimum total width, in columns, of any
window.  Its value has to accommodate two text columns as well as
margins, fringes, a scroll bar and a right divider, if present.
@end defopt

The following function tells how small a specific window can get taking
into account the sizes of its areas and the values of
@code{window-min-height}, @code{window-min-width} and
@code{window-size-fixed} (@pxref{Preserving Window Sizes}).

@defun window-min-size &optional window horizontal ignore pixelwise
This function returns the minimum size of @var{window}.  @var{window}
must be a valid window and defaults to the selected one.  The optional
argument @var{horizontal} non-@code{nil} means to return the minimum
number of columns of @var{window}; otherwise return the minimum number
of @var{window}'s lines.

The return value makes sure that all components of @var{window} remain
fully visible if @var{window}'s size were actually set to it.  With
@var{horizontal} @code{nil} it includes the mode and header line, the
horizontal scroll bar and the bottom divider, if present.  With
@var{horizontal} non-@code{nil} it includes the margins and fringes, the
vertical scroll bar and the right divider, if present.

The optional argument @var{ignore}, if non-@code{nil}, means ignore
restrictions imposed by fixed size windows, @code{window-min-height} or
@code{window-min-width} settings.  If @var{ignore} equals @code{safe},
live windows may get as small as @code{window-safe-min-height} lines and
@code{window-safe-min-width} columns.  If @var{ignore} is a window,
ignore restrictions for that window only.  Any other non-@code{nil}
value means ignore all of the above restrictions for all windows.

The optional argument @var{pixelwise} non-@code{nil} means to return the
minimum size of @var{window} counted in pixels.
@end defun


@node Resizing Windows
@section Resizing Windows
@cindex window resizing
@cindex resize window
@cindex changing window size
@cindex window size, changing

  This section describes functions for resizing a window without
changing the size of its frame.  Because live windows do not overlap,
these functions are meaningful only on frames that contain two or more
windows: resizing a window also changes the size of a neighboring
window.  If there is just one window on a frame, its size cannot be
changed except by resizing the frame (@pxref{Frame Size}).

  Except where noted, these functions also accept internal windows as
arguments.  Resizing an internal window causes its child windows to be
resized to fit the same space.

@defun window-resizable window delta &optional horizontal ignore pixelwise
This function returns @var{delta} if the size of @var{window} can be
changed vertically by @var{delta} lines.  If the optional argument
@var{horizontal} is non-@code{nil}, it instead returns @var{delta} if
@var{window} can be resized horizontally by @var{delta} columns.  It
does not actually change the window size.

If @var{window} is @code{nil}, it defaults to the selected window.

A positive value of @var{delta} means to check whether the window can be
enlarged by that number of lines or columns; a negative value of
@var{delta} means to check whether the window can be shrunk by that many
lines or columns.  If @var{delta} is non-zero, a return value of 0 means
that the window cannot be resized.

Normally, the variables @code{window-min-height} and
@code{window-min-width} specify the smallest allowable window size
(@pxref{Window Sizes}).  However, if the optional argument @var{ignore}
is non-@code{nil}, this function ignores @code{window-min-height} and
@code{window-min-width}, as well as @code{window-size-fixed}.  Instead,
it considers the minimum-height window to be one consisting of a header
and a mode line, a horizontal scrollbar and a bottom divider (if any),
plus a text area one line tall; and a minimum-width window as one
consisting of fringes, margins, a scroll bar and a right divider (if
any), plus a text area two columns wide.

If the optional argument @var{pixelwise} is non-@code{nil},
@var{delta} is interpreted as pixels.
@end defun

@defun window-resize window delta &optional horizontal ignore pixelwise
This function resizes @var{window} by @var{delta} increments.  If
@var{horizontal} is @code{nil}, it changes the height by @var{delta}
lines; otherwise, it changes the width by @var{delta} columns.  A
positive @var{delta} means to enlarge the window, and a negative
@var{delta} means to shrink it.

If @var{window} is @code{nil}, it defaults to the selected window.  If
the window cannot be resized as demanded, an error is signaled.

The optional argument @var{ignore} has the same meaning as for the
function @code{window-resizable} above.

If the optional argument @var{pixelwise} is non-@code{nil},
@var{delta} will be interpreted as pixels.

The choice of which window edges this function alters depends on the
values of the option @code{window-combination-resize} and the
combination limits of the involved windows; in some cases, it may alter
both edges.  @xref{Recombining Windows}.  To resize by moving only the
bottom or right edge of a window, use the function
@code{adjust-window-trailing-edge}.
@end defun

@c The commands enlarge-window, enlarge-window-horizontally,
@c shrink-window, and shrink-window-horizontally are documented in the
@c Emacs manual.  They are not preferred for calling from Lisp.

@defun adjust-window-trailing-edge window delta &optional horizontal pixelwise
This function moves @var{window}'s bottom edge by @var{delta} lines.
If optional argument @var{horizontal} is non-@code{nil}, it instead
moves the right edge by @var{delta} columns.  If @var{window} is
@code{nil}, it defaults to the selected window.

If the optional argument @var{pixelwise} is non-@code{nil},
@var{delta} is interpreted as pixels.

A positive @var{delta} moves the edge downwards or to the right; a
negative @var{delta} moves it upwards or to the left.  If the edge
cannot be moved as far as specified by @var{delta}, this function
moves it as far as possible but does not signal an error.

This function tries to resize windows adjacent to the edge that is
moved.  If this is not possible for some reason (e.g., if that adjacent
window is fixed-size), it may resize other windows.
@end defun

@cindex pixelwise, resizing windows
@defopt window-resize-pixelwise
If the value of this option is non-@code{nil}, Emacs resizes windows in
units of pixels.  This currently affects functions like
@code{split-window} (@pxref{Splitting Windows}), @code{maximize-window},
@code{minimize-window}, @code{fit-window-to-buffer},
@code{fit-frame-to-buffer} and
@code{shrink-window-if-larger-than-buffer} (all listed below).

Note that when a frame's pixel size is not a multiple of its character
size, at least one window may get resized pixelwise even if this
option is @code{nil}.  The default value is @code{nil}.
@end defopt

  The following commands resize windows in more specific ways.  When
called interactively, they act on the selected window.

@deffn Command fit-window-to-buffer &optional window max-height min-height max-width min-width preserve-size
This command adjusts the height or width of @var{window} to fit the text
in it.  It returns non-@code{nil} if it was able to resize @var{window},
and @code{nil} otherwise.  If @var{window} is omitted or @code{nil}, it
defaults to the selected window.  Otherwise, it should be a live window.

If @var{window} is part of a vertical combination, this function adjusts
@var{window}'s height.  The new height is calculated from the actual
height of the accessible portion of its buffer.  The optional argument
@var{max-height}, if non-@code{nil}, specifies the maximum total height
that this function can give @var{window}.  The optional argument
@var{min-height}, if non-@code{nil}, specifies the minimum total height
that it can give, which overrides the variable @code{window-min-height}.
Both @var{max-height} and @var{min-height} are specified in lines and
include mode and header line and a bottom divider, if any.

If @var{window} is part of a horizontal combination and the value of the
option @code{fit-window-to-buffer-horizontally} (see below) is
non-@code{nil}, this function adjusts @var{window}'s width.  The new
width of @var{window} is calculated from the maximum length of its
buffer's lines that follow the current start position of @var{window}.
The optional argument @var{max-width} specifies a maximum width and
defaults to the width of @var{window}'s frame.  The optional argument
@var{min-width} specifies a minimum width and defaults to
@code{window-min-width}.  Both @var{max-width} and @var{min-width} are
specified in columns and include fringes, margins and scrollbars, if
any.

The optional argument @var{preserve-size}, if non-@code{nil}, will
install a parameter to preserve the size of @var{window} during future
resize operations (@pxref{Preserving Window Sizes}).

If the option @code{fit-frame-to-buffer} (see below) is non-@code{nil},
this function will try to resize the frame of @var{window} to fit its
contents by calling @code{fit-frame-to-buffer} (see below).
@end deffn

@defopt fit-window-to-buffer-horizontally
If this is non-@code{nil}, @code{fit-window-to-buffer} can resize
windows horizontally.  If this is @code{nil} (the default)
@code{fit-window-to-buffer} never resizes windows horizontally.  If this
is @code{only}, it can resize windows horizontally only.  Any other
value means @code{fit-window-to-buffer} can resize windows in both
dimensions.
@end defopt

@defopt fit-frame-to-buffer
If this option is non-@code{nil}, @code{fit-window-to-buffer} can fit a
frame to its buffer.  A frame is fit if and only if its root window is a
live window and this option is non-@code{nil}.  If this is
@code{horizontally}, frames are fit horizontally only.  If this is
@code{vertically}, frames are fit vertically only.  Any other
non-@code{nil} value means frames can be resized in both dimensions.
@end defopt

If you have a frame that displays only one window, you can fit that
frame to its buffer using the command @code{fit-frame-to-buffer}.

@deffn Command fit-frame-to-buffer &optional frame max-height min-height max-width min-width only
This command adjusts the size of @var{frame} to display the contents of
its buffer exactly.  @var{frame} can be any live frame and defaults to
the selected one.  Fitting is done only if @var{frame}'s root window is
live.  The arguments @var{max-height}, @var{min-height}, @var{max-width}
and @var{min-width} specify bounds on the new total size of
@var{frame}'s root window.  @var{min-height} and @var{min-width} default
to the values of @code{window-min-height} and @code{window-min-width}
respectively.

If the optional argument @var{only} is @code{vertically}, this function
may resize the frame vertically only.  If @var{only} is
@code{horizontally}, it may resize the frame horizontally only.
@end deffn

The behavior of @code{fit-frame-to-buffer} can be controlled with the
help of the two options listed next.

@defopt fit-frame-to-buffer-margins
This option can be used to specify margins around frames to be fit by
@code{fit-frame-to-buffer}.  Such margins can be useful to avoid, for
example, that the resized frame overlaps the taskbar or parts of its
parent frame.

It specifies the numbers of pixels to be left free on the left, above,
the right, and below a frame that shall be fit.  The default specifies
@code{nil} for each which means to use no margins.  The value specified
here can be overridden for a specific frame by that frame's
@code{fit-frame-to-buffer-margins} parameter, if present.
@end defopt

@defopt fit-frame-to-buffer-sizes
This option specifies size boundaries for @code{fit-frame-to-buffer}.
It specifies the total maximum and minimum lines and maximum and minimum
columns of the root window of any frame that shall be fit to its buffer.
If any of these values is non-@code{nil}, it overrides the corresponding
argument of @code{fit-frame-to-buffer}.
@end defopt

@deffn Command shrink-window-if-larger-than-buffer &optional window
This command attempts to reduce @var{window}'s height as much as
possible while still showing its full buffer, but no less than
@code{window-min-height} lines.  The return value is non-@code{nil} if
the window was resized, and @code{nil} otherwise.  If @var{window} is
omitted or @code{nil}, it defaults to the selected window.  Otherwise,
it should be a live window.

This command does nothing if the window is already too short to
display all of its buffer, or if any of the buffer is scrolled
off-screen, or if the window is the only live window in its frame.

This command calls @code{fit-window-to-buffer} (see above) to do its
work.
@end deffn


@cindex balancing window sizes
@deffn Command balance-windows &optional window-or-frame
This function balances windows in a way that gives more space to
full-width and/or full-height windows.  If @var{window-or-frame}
specifies a frame, it balances all windows on that frame.  If
@var{window-or-frame} specifies a window, it balances only that window
and its siblings (@pxref{Windows and Frames}).
@end deffn

@deffn Command balance-windows-area
This function attempts to give all windows on the selected frame
approximately the same share of the screen area.  Full-width or
full-height windows are not given more space than other windows.
@end deffn

@cindex maximizing windows
@deffn Command maximize-window &optional window
This function attempts to make @var{window} as large as possible, in
both dimensions, without resizing its frame or deleting other windows.
If @var{window} is omitted or @code{nil}, it defaults to the selected
window.
@end deffn

@cindex minimizing windows
@deffn Command minimize-window &optional window
This function attempts to make @var{window} as small as possible, in
both dimensions, without deleting it or resizing its frame.  If
@var{window} is omitted or @code{nil}, it defaults to the selected
window.
@end deffn


@node Preserving Window Sizes
@section Preserving Window Sizes
@cindex preserving window sizes

A window can get resized explicitly by using one of the functions from
the preceding section or implicitly, for example, when resizing an
adjacent window, when splitting or deleting a window (@pxref{Splitting
Windows}, @pxref{Deleting Windows}) or when resizing the window's frame
(@pxref{Frame Size}).

  It is possible to avoid implicit resizing of a specific window when
there are one or more other resizable windows on the same frame.  For
this purpose, Emacs must be advised to @dfn{preserve} the size of that
window.  There are two basic ways to do that.

@defvar window-size-fixed
If this buffer-local variable is non-@code{nil}, the size of any window
displaying the buffer cannot normally be changed.  Deleting a window or
changing the frame's size may still change the window's size, if there
is no choice.

If the value is @code{height}, then only the window's height is fixed;
if the value is @code{width}, then only the window's width is fixed.
Any other non-@code{nil} value fixes both the width and the height.

If this variable is @code{nil}, this does not necessarily mean that any
window showing the buffer can be resized in the desired direction.  To
determine that, use the function @code{window-resizable}.
@xref{Resizing Windows}.
@end defvar

Often @code{window-size-fixed} is overly aggressive because it inhibits
any attempt to explicitly resize or split an affected window as well.
This may even happen after the window has been resized implicitly, for
example, when deleting an adjacent window or resizing the window's
frame.  The following function tries hard to never disallow resizing
such a window explicitly:

@defun window-preserve-size &optional window horizontal preserve
This function (un-)marks the height of window @var{window} as preserved
for future resize operations.  @var{window} must be a live window and
defaults to the selected one.  If the optional argument @var{horizontal}
is non-@code{nil}, it (un-)marks the width of @var{window} as preserved.

If the optional argument @var{preserve} is @code{t}, this means to
preserve the current height/width of @var{window}'s body.  The
height/width of @var{window} will change only if Emacs has no better
choice.  Resizing a window whose height/width is preserved by this
function never throws an error.

If @var{preserve} is @code{nil}, this means to stop preserving the
height/width of @var{window}, lifting any respective restraint induced
by a previous call of this function for @var{window}.  Calling
@code{enlarge-window}, @code{shrink-window} or
@code{fit-window-to-buffer} with @var{window} as argument may also
remove the respective restraint.
@end defun

@code{window-preserve-size} is currently invoked by the following
functions:

@table @code
@item fit-window-to-buffer
If the optional argument @var{preserve-size} of that function
(@pxref{Resizing Windows}) is non-@code{nil}, the size established by
that function is preserved.

@item display-buffer
If the @var{alist} argument of that function (@pxref{Choosing Window})
contains a @code{preserve-size} entry, the size of the window produced
by that function is preserved.
@end table

  @code{window-preserve-size} installs a window parameter (@pxref{Window
Parameters}) called @code{window-preserved-size} which is consulted by the
window resizing functions.  This parameter will not prevent resizing the
window when the window shows another buffer than the one when
@code{window-preserve-size} was invoked or if its size has changed since
then.

The following function can be used to check whether the height of a
particular window is preserved:

@defun window-preserved-size &optional window horizontal
This function returns the preserved height of window @var{window} in
pixels.  @var{window} must be a live window and defaults to the selected
one.  If the optional argument @var{horizontal} is non-@code{nil}, it
returns the preserved width of @var{window}.  It returns @code{nil} if
the size of @var{window} is not preserved.
@end defun


@node Splitting Windows
@section Splitting Windows
@cindex splitting windows
@cindex window splitting

This section describes functions for creating a new window by
@dfn{splitting} an existing one.  Note that some windows are special in
the sense that these functions may fail to split them as described here.
Examples of such windows are side windows (@pxref{Side Windows}) and
atomic windows (@pxref{Atomic Windows}).

@defun split-window &optional window size side pixelwise
This function creates a new live window next to the window
@var{window}.  If @var{window} is omitted or @code{nil}, it defaults
to the selected window.  That window is split, and reduced in
size.  The space is taken up by the new window, which is returned.

The optional second argument @var{size} determines the sizes of
@var{window} and/or the new window.  If it is omitted or @code{nil},
both windows are given equal sizes; if there is an odd line, it is
allocated to the new window.  If @var{size} is a positive number,
@var{window} is given @var{size} lines (or columns, depending on the
value of @var{side}).  If @var{size} is a negative number, the new
window is given @minus{}@var{size} lines (or columns).

If @var{size} is @code{nil}, this function obeys the variables
@code{window-min-height} and @code{window-min-width} (@pxref{Window
Sizes}).  Thus, it signals an error if splitting would result in making
a window smaller than those variables specify.  However, a
non-@code{nil} value for @var{size} causes those variables to be
ignored; in that case, the smallest allowable window is considered to be
one that has space for a text area one line tall and/or two columns
wide.

Hence, if @var{size} is specified, it's the caller's responsibility to
check whether the emanating windows are large enough to encompass all
areas like a mode line or a scroll bar.  The function
@code{window-min-size} (@pxref{Window Sizes}) can be used to determine
the minimum requirements of @var{window} in this regard.  Since the new
window usually inherits areas like the mode line or the scroll bar
from @var{window}, that function is also a good guess for the minimum
size of the new window.  The caller should specify a smaller size only
if it correspondingly removes an inherited area before the next
redisplay.

The optional third argument @var{side} determines the position of the
new window relative to @var{window}.  If it is @code{nil} or
@code{below}, the new window is placed below @var{window}.  If it is
@code{above}, the new window is placed above @var{window}.  In both
these cases, @var{size} specifies a total window height, in lines.

If @var{side} is @code{t} or @code{right}, the new window is placed on
the right of @var{window}.  If @var{side} is @code{left}, the new
window is placed on the left of @var{window}.  In both these cases,
@var{size} specifies a total window width, in columns.

The optional fourth argument @var{pixelwise}, if non-@code{nil}, means
to interpret @var{size} in units of pixels, instead of lines and
columns.

If @var{window} is a live window, the new window inherits various
properties from it, including margins and scroll bars.  If
@var{window} is an internal window, the new window inherits the
properties of the window selected within @var{window}'s frame.

The behavior of this function may be altered by the window parameters
of @var{window}, so long as the variable
@code{ignore-window-parameters} is @code{nil}.  If the value of
the @code{split-window} window parameter is @code{t}, this function
ignores all other window parameters.  Otherwise, if the value of the
@code{split-window} window parameter is a function, that function is
called with the arguments @var{window}, @var{size}, and @var{side}, in
lieu of the usual action of @code{split-window}.  Otherwise, this
function obeys the @code{window-atom} or @code{window-side} window
parameter, if any.  @xref{Window Parameters}.
@end defun

  As an example, here is a sequence of @code{split-window} calls that
yields the window configuration discussed in @ref{Windows and Frames}.
This example demonstrates splitting a live window as well as splitting
an internal window.  We begin with a frame containing a single window
(a live root window), which we denote by @var{W4}.  Calling
@code{(split-window W4)} yields this window configuration:

@smallexample
@group
     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W4_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W5_________________||
    |__________________W3__________________|

@end group
@end smallexample

@noindent
The @code{split-window} call has created a new live window, denoted by
@var{W5}.  It has also created a new internal window, denoted by
@var{W3}, which becomes the root window and the parent of both
@var{W4} and @var{W5}.

  Next, we call @code{(split-window W3 nil 'left)}, passing the
internal window @var{W3} as the argument.  The result:

@smallexample
@group
     ______________________________________
    | ______  ____________________________ |
    ||      || __________________________ ||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||____________W4____________|||
    ||      || __________________________ ||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||____________W5____________|||
    ||__W2__||_____________W3_____________ |
    |__________________W1__________________|
@end group
@end smallexample

@noindent
A new live window @var{W2} is created, to the left of the internal
window @var{W3}.  A new internal window @var{W1} is created, becoming
the new root window.

   For interactive use, Emacs provides two commands which always split
the selected window.  These call @code{split-window} internally.

@deffn Command split-window-right &optional size
This function splits the selected window into two side-by-side
windows, putting the selected window on the left.  If @var{size} is
positive, the left window gets @var{size} columns; if @var{size} is
negative, the right window gets @minus{}@var{size} columns.
@end deffn

@deffn Command split-window-below &optional size
This function splits the selected window into two windows, one above
the other, leaving the upper window selected.  If @var{size} is
positive, the upper window gets @var{size} lines; if @var{size} is
negative, the lower window gets @minus{}@var{size} lines.
@end deffn

@defopt split-window-keep-point
If the value of this variable is non-@code{nil} (the default),
@code{split-window-below} behaves as described above.

If it is @code{nil}, @code{split-window-below} adjusts point in each
of the two windows to minimize redisplay.  (This is useful on slow
terminals.)  It selects whichever window contains the screen line that
point was previously on.  Note that this only affects
@code{split-window-below}, not the lower-level @code{split-window}
function.
@end defopt


@node Deleting Windows
@section Deleting Windows
@cindex deleting windows

  @dfn{Deleting} a window removes it from the frame's window tree.  If
the window is a live window, it disappears from the screen.  If the
window is an internal window, its child windows are deleted too.

  Even after a window is deleted, it continues to exist as a Lisp
object, until there are no more references to it.  Window deletion can
be reversed, by restoring a saved window configuration (@pxref{Window
Configurations}).

@deffn Command delete-window &optional window
This function removes @var{window} from display and returns
@code{nil}.  If @var{window} is omitted or @code{nil}, it defaults to
the selected window.

If deleting the window would leave no more windows in the window tree
(e.g., if it is the only live window in the frame) or all remaining
windows on @var{window}'s frame are side windows (@pxref{Side
Windows}), an error is signaled.  If @var{window} is part of an atomic
window (@pxref{Atomic Windows}), this function tries to delete the
root of that atomic window instead.

By default, the space taken up by @var{window} is given to one of its
adjacent sibling windows, if any.  However, if the variable
@code{window-combination-resize} is non-@code{nil}, the space is
proportionally distributed among any remaining windows in the same
window combination.  @xref{Recombining Windows}.

The behavior of this function may be altered by the window parameters of
@var{window}, so long as the variable @code{ignore-window-parameters} is
@code{nil}.  If the value of the @code{delete-window} window parameter
is @code{t}, this function ignores all other window parameters.
Otherwise, if the value of the @code{delete-window} window parameter is
a function, that function is called with the argument @var{window}, in
lieu of the usual action of @code{delete-window}.  @xref{Window
Parameters}.
@end deffn

@deffn Command delete-other-windows &optional window
This function makes @var{window} fill its frame, deleting other
windows as necessary.  If @var{window} is omitted or @code{nil}, it
defaults to the selected window.  An error is signaled if @var{window}
is a side window (@pxref{Side Windows}).  If @var{window} is part of
an atomic window (@pxref{Atomic Windows}), this function tries to make
the root of that atomic window fill its frame.  The return
value is @code{nil}.

The behavior of this function may be altered by the window parameters of
@var{window}, so long as the variable @code{ignore-window-parameters} is
@code{nil}.  If the value of the @code{delete-other-windows} window
parameter is @code{t}, this function ignores all other window
parameters.  Otherwise, if the value of the @code{delete-other-windows}
window parameter is a function, that function is called with the
argument @var{window}, in lieu of the usual action of
@code{delete-other-windows}.  @xref{Window Parameters}.

Also, if @code{ignore-window-parameters} is @code{nil}, this function
does not delete any window whose @code{no-delete-other-windows}
parameter is non-@code{nil}.
@end deffn

@deffn Command delete-windows-on &optional buffer-or-name frame
This function deletes all windows showing @var{buffer-or-name}, by
calling @code{delete-window} on those windows.  @var{buffer-or-name}
should be a buffer, or the name of a buffer; if omitted or @code{nil},
it defaults to the current buffer.  If there are no windows showing
the specified buffer, this function does nothing.  If the specified
buffer is a minibuffer, an error is signaled.

If there is a dedicated window showing the buffer, and that window is
the only one on its frame, this function also deletes that frame if it
is not the only frame on the terminal.

The optional argument @var{frame} specifies which frames to operate
on:

@itemize @bullet
@item @code{nil}
means operate on all frames.
@item @code{t}
means operate on the selected frame.
@item @code{visible}
means operate on all visible frames.
@item @code{0}
means operate on all visible or iconified frames.
@item A frame
means operate on that frame.
@end itemize

Note that this argument does not have the same meaning as in other
functions which scan all live windows (@pxref{Cyclic Window
Ordering}).  Specifically, the meanings of @code{t} and @code{nil} here
are the opposite of what they are in those other functions.
@end deffn


@node Recombining Windows
@section Recombining Windows
@cindex recombining windows
@cindex windows, recombining

When deleting the last sibling of a window @var{W}, its parent window
is deleted too, with @var{W} replacing it in the window tree.  This
means that @var{W} must be recombined with its parent's siblings to
form a new window combination (@pxref{Windows and Frames}).  In some
occasions, deleting a live window may even entail the deletion of two
internal windows.

@smallexample
@group
     ______________________________________
    | ______  ____________________________ |
    ||      || __________________________ ||
    ||      ||| ___________  ___________ |||
    ||      ||||           ||           ||||
    ||      ||||____W6_____||_____W7____||||
    ||      |||____________W4____________|||
    ||      || __________________________ ||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||____________W5____________|||
    ||__W2__||_____________W3_____________ |
    |__________________W1__________________|

@end group
@end smallexample

@noindent
Deleting @var{W5} in this configuration normally causes the deletion of
@var{W3} and @var{W4}.  The remaining live windows @var{W2},
@var{W6} and @var{W7} are recombined to form a new horizontal
combination with parent @var{W1}.

   Sometimes, however, it makes sense to not delete a parent window like
@var{W4}.  In particular, a parent window should not be removed when it
was used to preserve a combination embedded in a combination of the same
type.  Such embeddings make sense to assure that when you split a window
and subsequently delete the new window, Emacs reestablishes the layout
of the associated frame as it existed before the splitting.

   Consider a scenario starting with two live windows @var{W2} and
@var{W3} and their parent @var{W1}.

@smallexample
@group
     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W3_________________||
    |__________________W1__________________|

@end group
@end smallexample

@noindent
Split @var{W2} to make a new window @var{W4} as follows.

@smallexample
@group
     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W4_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W3_________________||
    |__________________W1__________________|

@end group
@end smallexample

@noindent
Now, when enlarging a window vertically, Emacs tries to obtain the
corresponding space from its lower sibling, provided such a window
exists.  In our scenario, enlarging @var{W4} will steal space from
@var{W3}.

@smallexample
@group
     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W4_________________||
    | ____________________________________ |
    ||_________________W3_________________||
    |__________________W1__________________|

@end group
@end smallexample

@noindent
Deleting @var{W4} will now give its entire space to @var{W2},
including the space earlier stolen from @var{W3}.

@smallexample
@group
     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||_________________W3_________________||
    |__________________W1__________________|

@end group
@end smallexample

@noindent
This can be counterintuitive, in particular if @var{W4} were used for
displaying a buffer only temporarily (@pxref{Temporary Displays}), and
you want to continue working with the initial layout.

The behavior can be fixed by making a new parent window when splitting
@var{W2}.  The variable described next allows that to be done.

@defopt window-combination-limit
This variable controls whether splitting a window shall make a new
parent window.  The following values are recognized:

@table @code
@item nil
This means that the new live window is allowed to share the existing
parent window, if one exists, provided the split occurs in the same
direction as the existing window combination (otherwise, a new internal
window is created anyway).

@item window-size
This means that @code{display-buffer} makes a new parent window when
it splits a window and is passed a @code{window-height} or
@code{window-width} entry in the @var{alist} argument (@pxref{Buffer
Display Action Functions}).  Otherwise, window splitting behaves as
for a value of @code{nil}.

@item temp-buffer-resize
In this case @code{with-temp-buffer-window} makes a new parent window
when it splits a window and @code{temp-buffer-resize-mode} is enabled
(@pxref{Temporary Displays}).  Otherwise, window splitting behaves as
for @code{nil}.

@item temp-buffer
In this case @code{with-temp-buffer-window} always makes a new parent
window when it splits an existing window (@pxref{Temporary Displays}).
Otherwise, window splitting behaves as for @code{nil}.

@item display-buffer
This means that when @code{display-buffer} (@pxref{Choosing Window})
splits a window it always makes a new parent window.  Otherwise, window
splitting behaves as for @code{nil}.

@item t
This means that splitting a window always creates a new parent window.
Thus, if the value of this variable is at all times @code{t}, then at
all times every window tree is a binary tree (a tree where each window
except the root window has exactly one sibling).
@end table

The default is @code{window-size}.  Other values are reserved for future
use.

If, as a consequence of this variable's setting, @code{split-window}
makes a new parent window, it also calls
@code{set-window-combination-limit} (see below) on the newly-created
internal window.  This affects how the window tree is rearranged when
the child windows are deleted (see below).
@end defopt

  If @code{window-combination-limit} is @code{t}, splitting @var{W2} in
the initial configuration of our scenario would have produced this:

@smallexample
@group
     ______________________________________
    | ____________________________________ |
    || __________________________________ ||
    |||                                  |||
    |||________________W2________________|||
    || __________________________________ ||
    |||                                  |||
    |||________________W4________________|||
    ||_________________W5_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W3_________________||
    |__________________W1__________________|

@end group
@end smallexample

@noindent
A new internal window @var{W5} has been created; its children are
@var{W2} and the new live window @var{W4}.  Now, @var{W2} is the only
sibling of @var{W4}, so enlarging @var{W4} will try to shrink
@var{W2}, leaving @var{W3} unaffected.  Observe that @var{W5}
represents a vertical combination of two windows embedded in the
vertical combination @var{W1}.

@cindex window combination limit
@defun set-window-combination-limit window limit
This function sets the @dfn{combination limit} of the window
@var{window} to @var{limit}.  This value can be retrieved via the
function @code{window-combination-limit}.  See below for its effects;
note that it is only meaningful for internal windows.  The
@code{split-window} function automatically calls this function, passing
it @code{t} as @var{limit}, provided the value of the variable
@code{window-combination-limit} is @code{t} when it is called.
@end defun

@defun window-combination-limit window
This function returns the combination limit for @var{window}.

The combination limit is meaningful only for an internal window.  If it
is @code{nil}, then Emacs is allowed to automatically delete
@var{window}, in response to a window deletion, in order to group the
child windows of @var{window} with its sibling windows to form a new
window combination.  If the combination limit is @code{t}, the child
windows of @var{window} are never automatically recombined with its
siblings.

If, in the configuration shown at the beginning of this section, the
combination limit of @var{W4} (the parent window of @var{W6} and
@var{W7}) is @code{t}, deleting @var{W5} will not implicitly delete
@var{W4} too.
@end defun

Alternatively, the problems sketched above can be avoided by always
resizing all windows in the same combination whenever one of its windows
is split or deleted.  This also permits splitting windows that would be
otherwise too small for such an operation.

@defopt window-combination-resize
If this variable is @code{nil}, @code{split-window} can only split a
window (denoted by @var{window}) if @var{window}'s screen area is large
enough to accommodate both itself and the new window.

If this variable is @code{t}, @code{split-window} tries to resize all
windows that are part of the same combination as @var{window}, in order
to accommodate the new window.  In particular, this may allow
@code{split-window} to succeed even if @var{window} is a fixed-size
window or too small to ordinarily split.  Furthermore, subsequently
resizing or deleting @var{window} may resize all other windows in its
combination.

The default is @code{nil}.  Other values are reserved for future use.  A
specific split operation may ignore the value of this variable if it is
affected by a non-@code{nil} value of @code{window-combination-limit}.
@end defopt

  To illustrate the effect of @code{window-combination-resize}, consider
the following frame layout.

@smallexample
@group
     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W3_________________||
    |__________________W1__________________|

@end group
@end smallexample

@noindent
If @code{window-combination-resize} is @code{nil}, splitting window
@var{W3} leaves the size of @var{W2} unchanged:

@smallexample
@group
     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||_________________W3_________________||
    | ____________________________________ |
    ||                                    ||
    ||_________________W4_________________||
    |__________________W1__________________|

@end group
@end smallexample

@noindent
If @code{window-combination-resize} is @code{t}, splitting @var{W3}
instead leaves all three live windows with approximately the same
height:

@smallexample
@group
     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W3_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W4_________________||
    |__________________W1__________________|

@end group
@end smallexample

@noindent
Deleting any of the live windows @var{W2}, @var{W3} or @var{W4} will
distribute its space proportionally among the two remaining live
windows.


@node Selecting Windows
@section Selecting Windows
@cindex selecting a window

@defun select-window window &optional norecord
This function makes @var{window} the selected window and the window
selected within its frame (@pxref{Basic Windows}), and selects that
frame.  It also makes @var{window}'s buffer (@pxref{Buffers and
Windows}) current and sets that buffer's value of @code{point} to the
value of @code{window-point} (@pxref{Window Point}) in @var{window}.
@var{window} must be a live window.  The return value is @var{window}.

By default, this function also moves @var{window}'s buffer to the front
of the buffer list (@pxref{Buffer List}) and makes @var{window} the most
recently selected window.  If the optional argument @var{norecord} is
non-@code{nil}, these additional actions are omitted.

In addition, this function by default also tells the display engine to
update the display of @var{window} when its frame gets redisplayed the
next time.  If @var{norecord} is non-@code{nil}, such updates are
usually not performed.  If, however, @var{norecord} equals the special
symbol @code{mark-for-redisplay}, the additional actions mentioned above
are omitted but @var{window} will be nevertheless updated.

Note that sometimes selecting a window is not enough to show it, or
make its frame the top-most frame on display: you may also need to
raise the frame or make sure input focus is directed to that frame.
@xref{Input Focus}.
@end defun

@cindex select window hooks
@cindex running a hook when a window gets selected
For historical reasons, Emacs does not run a separate hook whenever a
window gets selected.  Applications and internal routines often
temporarily select a window to perform a few actions on it.  They do
that either to simplify coding---because many functions by default
operate on the selected window when no @var{window} argument is
specified---or because some functions did not (and still do not) take a
window as argument and always operate(d) on the selected window instead.
Running a hook every time a window gets selected for a short time and
once more when the previously selected window gets restored is not
useful.

  However, when its @var{norecord} argument is @code{nil},
@code{select-window} updates the buffer list and thus indirectly runs
the normal hook @code{buffer-list-update-hook} (@pxref{Buffer List}).
Consequently, that hook provides one way to run a function whenever a
window gets selected more ``permanently''.

  Since @code{buffer-list-update-hook} is also run by functions that are
not related to window management, it will usually make sense to save the
value of the selected window somewhere and compare it with the value of
@code{selected-window} while running that hook.  Also, to avoid false
positives when using @code{buffer-list-update-hook}, it is good practice
that every @code{select-window} call supposed to select a window only
temporarily passes a non-@code{nil} @var{norecord} argument.  If
possible, the macro @code{with-selected-window} (see below) should be
used in such cases.

  Emacs also runs the hook @code{window-selection-change-functions}
whenever the redisplay routine detects that another window has been
selected since last redisplay.  @xref{Window Hooks}, for a detailed
explanation.  @code{window-state-change-functions} (described in the
same section) is another abnormal hook run after a different window
has been selected but is triggered by other window changes as well.

@cindex most recently selected windows
  The sequence of calls to @code{select-window} with a non-@code{nil}
@var{norecord} argument determines an ordering of windows by their
selection time.  The function @code{get-lru-window} can be used to
retrieve the least recently selected live window (@pxref{Cyclic Window
Ordering}).

@defmac save-selected-window forms@dots{}
This macro records the selected frame, as well as the selected window
of each frame, executes @var{forms} in sequence, then restores the
earlier selected frame and windows.  It also saves and restores the
current buffer.  It returns the value of the last form in @var{forms}.

This macro does not save or restore anything about the sizes,
arrangement or contents of windows; therefore, if @var{forms} change
them, the change persists.  If the previously selected window of some
frame is no longer live at the time of exit from @var{forms}, that
frame's selected window is left alone.  If the previously selected
window is no longer live, then whatever window is selected at the end of
@var{forms} remains selected.  The current buffer is restored if and
only if it is still live when exiting @var{forms}.

This macro changes neither the ordering of recently selected windows nor
the buffer list.
@end defmac

@defmac with-selected-window window forms@dots{}
This macro selects @var{window}, executes @var{forms} in sequence, then
restores the previously selected window and current buffer.  The
ordering of recently selected windows and the buffer list remain
unchanged unless you deliberately change them within @var{forms}; for
example, by calling @code{select-window} with argument @var{norecord}
@code{nil}.  Hence, this macro is the preferred way to temporarily work
with @var{window} as the selected window without needlessly running
@code{buffer-list-update-hook}.
@end defmac

@defun frame-selected-window &optional frame
This function returns the window on @var{frame} that is selected
within that frame.  @var{frame} should be a live frame; if omitted or
@code{nil}, it defaults to the selected frame.
@end defun

@defun set-frame-selected-window frame window &optional norecord
This function makes @var{window} the window selected within the frame
@var{frame}.  @var{frame} should be a live frame; if @code{nil}, it
defaults to the selected frame.  @var{window} should be a live window;
if @code{nil}, it defaults to the selected window.

If @var{frame} is the selected frame, this makes @var{window} the
selected window.

If the optional argument @var{norecord} is non-@code{nil}, this
function does not alter the list of most recently selected windows,
nor the buffer list.
@end defun

@cindex window use time
@cindex use time of window
@cindex window order by time of last use
@defun window-use-time &optional window
This functions returns the use time of window @var{window}.
@var{window} must be a live window and defaults to the selected one.

The @dfn{use time} of a window is not really a time value, but an
integer that does increase monotonically with each call of
@code{select-window} with a @code{nil} @var{norecord} argument.  The
window with the lowest use time is usually called the least recently
used window while the window with the highest use time is called the
most recently used one (@pxref{Cyclic Window Ordering}).
@end defun


@node Cyclic Window Ordering
@section Cyclic Ordering of Windows
@cindex cyclic ordering of windows
@cindex ordering of windows, cyclic
@cindex window ordering, cyclic

  When you use the command @w{@kbd{C-x o}} (@code{other-window}) to select
some other window, it moves through live windows in a specific order.
For any given configuration of windows, this order never varies.  It
is called the @dfn{cyclic ordering of windows}.

  The ordering is determined by a depth-first traversal of each frame's
window tree, retrieving the live windows which are the leaf nodes of the
tree (@pxref{Windows and Frames}).  If the minibuffer is active, the
minibuffer window is included too.  The ordering is cyclic, so the last
window in the sequence is followed by the first one.

@defun next-window &optional window minibuf all-frames
@cindex minibuffer window, and @code{next-window}
This function returns a live window, the one following @var{window} in
the cyclic ordering of windows.  @var{window} should be a live window;
if omitted or @code{nil}, it defaults to the selected window.

The optional argument @var{minibuf} specifies whether minibuffer windows
should be included in the cyclic ordering.  Normally, when @var{minibuf}
is @code{nil}, a minibuffer window is included only if it is currently
active; this matches the behavior of @w{@kbd{C-x o}}.  (Note that a
minibuffer window is active as long as its minibuffer is in use; see
@ref{Minibuffers}).

If @var{minibuf} is @code{t}, the cyclic ordering includes all
minibuffer windows.  If @var{minibuf} is neither @code{t} nor
@code{nil}, minibuffer windows are not included even if they are active.

The optional argument @var{all-frames} specifies which frames to
consider:

@itemize @bullet
@item @code{nil}
means to consider windows on @var{window}'s frame.  If the minibuffer
window is considered (as specified by the @var{minibuf} argument),
then frames that share the minibuffer window are considered too.

@item @code{t}
means to consider windows on all existing frames.

@item @code{visible}
means to consider windows on all visible frames.

@item 0
means to consider windows on all visible or iconified frames.

@item A frame
means to consider windows on that specific frame.

@item Anything else
means to consider windows on @var{window}'s frame, and no others.
@end itemize

If more than one frame is considered, the cyclic ordering is obtained
by appending the orderings for those frames, in the same order as the
list of all live frames (@pxref{Finding All Frames}).
@end defun

@defun previous-window &optional window minibuf all-frames
This function returns a live window, the one preceding @var{window} in
the cyclic ordering of windows.  The other arguments are handled like
in @code{next-window}.
@end defun

@deffn Command other-window count &optional all-frames
This function selects a live window, one @var{count} places from the
selected window in the cyclic ordering of windows.  If @var{count} is
a positive number, it skips @var{count} windows forwards; if
@var{count} is negative, it skips @minus{}@var{count} windows
backwards; if @var{count} is zero, that simply re-selects the selected
window.  When called interactively, @var{count} is the numeric prefix
argument.

The optional argument @var{all-frames} has the same meaning as in
@code{next-window}, like a @code{nil} @var{minibuf} argument to
@code{next-window}.

This function does not select a window that has a non-@code{nil}
@code{no-other-window} window parameter (@pxref{Window Parameters}),
provided that @code{ignore-window-parameters} is @code{nil}.

If the @code{other-window} parameter of the selected window is a
function, and @code{ignore-window-parameters} is @code{nil}, that
function will be called with the arguments @var{count} and
@var{all-frames} instead of the normal operation of this function.
@end deffn

@defun walk-windows fun &optional minibuf all-frames
This function calls the function @var{fun} once for each live window,
with the window as the argument.

It follows the cyclic ordering of windows.  The optional arguments
@var{minibuf} and @var{all-frames} specify the set of windows
included; these have the same arguments as in @code{next-window}.  If
@var{all-frames} specifies a frame, the first window walked is the
first window on that frame (the one returned by
@code{frame-first-window}), not necessarily the selected window.

If @var{fun} changes the window configuration by splitting or deleting
windows, that does not alter the set of windows walked, which is
determined prior to calling @var{fun} for the first time.
@end defun

@defun one-window-p &optional no-mini all-frames
This function returns @code{t} if the selected window is the only live
window, and @code{nil} otherwise.

If the minibuffer window is active, it is normally considered (so that
this function returns @code{nil}).  However, if the optional argument
@var{no-mini} is non-@code{nil}, the minibuffer window is ignored even
if active.  The optional argument @var{all-frames} has the same
meaning as for @code{next-window}.
@end defun

@cindex finding windows
  The following functions return a window which satisfies some
criterion, without selecting it:

@cindex least recently used window
@defun get-lru-window &optional all-frames dedicated not-selected
This function returns a live window which is heuristically the least
recently used.  The optional argument @var{all-frames} has
the same meaning as in @code{next-window}.

If any full-width windows are present, only those windows are
considered.  A minibuffer window is never a candidate.  A dedicated
window (@pxref{Dedicated Windows}) is never a candidate unless the
optional argument @var{dedicated} is non-@code{nil}.  The selected
window is never returned, unless it is the only candidate.  However, if
the optional argument @var{not-selected} is non-@code{nil}, this
function returns @code{nil} in that case.
@end defun

@cindex most recently used window
@defun get-mru-window &optional all-frames dedicated not-selected
This function is like @code{get-lru-window}, but it returns the most
recently used window instead.  The meaning of the arguments is the
same as described for @code{get-lru-window}.
@end defun

@cindex largest window
@defun get-largest-window &optional all-frames dedicated not-selected
This function returns the window with the largest area (height times
width).  The optional argument @var{all-frames} specifies the windows to
search, and has the same meaning as in @code{next-window}.

A minibuffer window is never a candidate.  A dedicated window
(@pxref{Dedicated Windows}) is never a candidate unless the optional
argument @var{dedicated} is non-@code{nil}.  The selected window is not
a candidate if the optional argument @var{not-selected} is
non-@code{nil}.  If the optional argument @var{not-selected} is
non-@code{nil} and the selected window is the only candidate, this
function returns @code{nil}.

If there are two candidate windows of the same size, this function
prefers the one that comes first in the cyclic ordering of windows,
starting from the selected window.
@end defun

@cindex window that satisfies a predicate
@cindex conditional selection of windows
@defun get-window-with-predicate predicate &optional minibuf all-frames default
This function calls the function @var{predicate} for each of the
windows in the cyclic order of windows in turn, passing it the window
as an argument.  If the predicate returns non-@code{nil} for any
window, this function stops and returns that window.  If no such
window is found, the return value is @var{default} (which defaults to
@code{nil}).

The optional arguments @var{minibuf} and @var{all-frames} specify the
windows to search, and have the same meanings as in
@code{next-window}.
@end defun


@node Buffers and Windows
@section Buffers and Windows
@cindex examining windows
@cindex windows, controlling precisely
@cindex buffers, controlled in windows

  This section describes low-level functions for examining and setting
the contents of windows.  @xref{Switching Buffers}, for higher-level
functions for displaying a specific buffer in a window.

@defun window-buffer &optional window
This function returns the buffer that @var{window} is displaying.  If
@var{window} is omitted or @code{nil} it defaults to the selected
window.  If @var{window} is an internal window, this function returns
@code{nil}.
@end defun

@defun set-window-buffer window buffer-or-name &optional keep-margins
This function makes @var{window} display @var{buffer-or-name}.
@var{window} should be a live window; if @code{nil}, it defaults to
the selected window.  @var{buffer-or-name} should be a buffer, or the
name of an existing buffer.  This function does not change which
window is selected, nor does it directly change which buffer is
current (@pxref{Current Buffer}).  Its return value is @code{nil}.

If @var{window} is @dfn{strongly dedicated} to a buffer and
@var{buffer-or-name} does not specify that buffer, this function
signals an error.  @xref{Dedicated Windows}.

By default, this function resets @var{window}'s position, display
margins, fringe widths, and scroll bar settings, based on the local
variables in the specified buffer.  However, if the optional argument
@var{keep-margins} is non-@code{nil}, it leaves @var{window}'s display
margins, fringes and scroll bar settings alone.

When writing an application, you should normally use
@code{display-buffer} (@pxref{Choosing Window}) or the higher-level
functions described in @ref{Switching Buffers}, instead of calling
@code{set-window-buffer} directly.

This runs @code{window-scroll-functions}, followed by
@code{window-configuration-change-hook}.  @xref{Window Hooks}.
@end defun

@defvar buffer-display-count
This buffer-local variable records the number of times a buffer has been
displayed in a window.  It is incremented each time
@code{set-window-buffer} is called for the buffer.
@end defvar

@defvar buffer-display-time
This buffer-local variable records the time at which a buffer was last
displayed in a window.  The value is @code{nil} if the buffer has
never been displayed.  It is updated each time
@code{set-window-buffer} is called for the buffer, with the value
returned by @code{current-time} (@pxref{Time of Day}).
@end defvar

@defun get-buffer-window &optional buffer-or-name all-frames
This function returns the first window displaying @var{buffer-or-name}
in the cyclic ordering of windows, starting from the selected window
(@pxref{Cyclic Window Ordering}).  If no such window exists, the
return value is @code{nil}.

@var{buffer-or-name} should be a buffer or the name of a buffer; if
omitted or @code{nil}, it defaults to the current buffer.  The
optional argument @var{all-frames} specifies which windows to
consider:

@itemize @bullet
@item
@code{t} means consider windows on all existing frames.
@item
@code{visible} means consider windows on all visible frames.
@item
0 means consider windows on all visible or iconified frames.
@item
A frame means consider windows on that frame only.
@item
Any other value means consider windows on the selected frame.
@end itemize

Note that these meanings differ slightly from those of the
@var{all-frames} argument to @code{next-window} (@pxref{Cyclic Window
Ordering}).  This function may be changed in a future version of Emacs
to eliminate this discrepancy.
@end defun

@defun get-buffer-window-list &optional buffer-or-name minibuf all-frames
This function returns a list of all windows currently displaying
@var{buffer-or-name}.  @var{buffer-or-name} should be a buffer or the
name of an existing buffer.  If omitted or @code{nil}, it defaults to
the current buffer.  If the currently selected window displays
@var{buffer-or-name}, it will be the first in the list returned by
this function.

The arguments @var{minibuf} and @var{all-frames} have the same
meanings as in the function @code{next-window} (@pxref{Cyclic Window
Ordering}).  Note that the @var{all-frames} argument does @emph{not}
behave exactly like in @code{get-buffer-window}.
@end defun

@deffn Command replace-buffer-in-windows &optional buffer-or-name
This command replaces @var{buffer-or-name} with some other buffer, in
all windows displaying it.  @var{buffer-or-name} should be a buffer, or
the name of an existing buffer; if omitted or @code{nil}, it defaults to
the current buffer.

The replacement buffer in each window is chosen via
@code{switch-to-prev-buffer} (@pxref{Window History}).  Any dedicated
window displaying @var{buffer-or-name} is deleted if possible
(@pxref{Dedicated Windows}).  If such a window is the only window on its
frame and there are other frames on the same terminal, the frame is
deleted as well.  If the dedicated window is the only window on the only
frame on its terminal, the buffer is replaced anyway.
@end deffn


@node Switching Buffers
@section Switching to a Buffer in a Window
@cindex switching to a buffer

This section describes high-level functions for switching to a specified
buffer in some window.  In general, ``switching to a buffer'' means to
(1) show the buffer in some window, (2) make that window the selected
window (and its frame the selected frame), and (3) make the buffer the
current buffer.

  Do @emph{not} use these functions to make a buffer temporarily
current just so a Lisp program can access or modify it.  They have
side-effects, such as changing window histories (@pxref{Window
History}), which will surprise the user if used that way.  If you want
to make a buffer current to modify it in Lisp, use
@code{with-current-buffer}, @code{save-current-buffer}, or
@code{set-buffer}.  @xref{Current Buffer}.

@deffn Command switch-to-buffer buffer-or-name &optional norecord force-same-window
This command attempts to display @var{buffer-or-name} in the selected
window and make it the current buffer.  It is often used interactively
(as the binding of @kbd{C-x b}), as well as in Lisp programs.  The
return value is the buffer switched to.

If @var{buffer-or-name} is @code{nil}, it defaults to the buffer
returned by @code{other-buffer} (@pxref{Buffer List}).  If
@var{buffer-or-name} is a string that is not the name of any existing
buffer, this function creates a new buffer with that name; the new
buffer's major mode is determined by the variable @code{major-mode}
(@pxref{Major Modes}).

Normally, the specified buffer is put at the front of the buffer
list---both the global buffer list and the selected frame's buffer
list (@pxref{Buffer List}).  However, this is not done if the
optional argument @var{norecord} is non-@code{nil}.

Sometimes, the selected window may not be suitable for displaying the
buffer.  This happens if the selected window is a minibuffer window, or
if the selected window is strongly dedicated to its buffer
(@pxref{Dedicated Windows}).  In such cases, the command normally tries
to display the buffer in some other window, by invoking
@code{pop-to-buffer} (see below).

If the optional argument @var{force-same-window} is non-@code{nil} and
the selected window is not suitable for displaying the buffer, this
function always signals an error when called non-interactively.  In
interactive use, if the selected window is a minibuffer window, this
function will try to use some other window instead.  If the selected
window is strongly dedicated to its buffer, the option
@code{switch-to-buffer-in-dedicated-window} described next can be used
to proceed.
@end deffn

@defopt switch-to-buffer-in-dedicated-window
This option, if non-@code{nil}, allows @code{switch-to-buffer} to
proceed when called interactively and the selected window is strongly
dedicated to its buffer.

The following values are respected:

@table @code
@item nil
Disallows switching and signals an error as in non-interactive use.

@item prompt
Prompts the user whether to allow switching.

@item pop
Invokes @code{pop-to-buffer} to proceed.

@item t
Marks the selected window as non-dedicated and proceeds.
@end table

This option does not affect non-interactive calls of
@code{switch-to-buffer}.
@end defopt

By default, @code{switch-to-buffer} tries to preserve
@code{window-point}.  This behavior can be tuned using the following
option.

@defopt switch-to-buffer-preserve-window-point
If this variable is @code{nil}, @code{switch-to-buffer} displays the
buffer specified by @var{buffer-or-name} at the position of that
buffer's @code{point}.  If this variable is @code{already-displayed}, it
tries to display the buffer at its previous position in the selected
window, provided the buffer is currently displayed in some other window
on any visible or iconified frame.  If this variable is @code{t},
@code{switch-to-buffer} unconditionally tries to display the buffer at
its previous position in the selected window.

This variable is ignored if the buffer is already displayed in the
selected window or never appeared in it before, or if
@code{switch-to-buffer} calls @code{pop-to-buffer} to display the
buffer.
@end defopt

@defopt switch-to-buffer-obey-display-actions
If this variable is non-@code{nil}, @code{switch-to-buffer} respects
display actions specified by @code{display-buffer-overriding-action},
@code{display-buffer-alist} and other display related variables.
@end defopt

The next two commands are similar to @code{switch-to-buffer}, except for
the described features.

@deffn Command switch-to-buffer-other-window buffer-or-name &optional norecord
This function displays the buffer specified by @var{buffer-or-name} in
some window other than the selected window.  It uses the function
@code{pop-to-buffer} internally (see below).

If the selected window already displays the specified buffer, it
continues to do so, but another window is nonetheless found to display
it as well.

The @var{buffer-or-name} and @var{norecord} arguments have the same
meanings as in @code{switch-to-buffer}.
@end deffn

@deffn Command switch-to-buffer-other-frame buffer-or-name &optional norecord
This function displays the buffer specified by @var{buffer-or-name} in a
new frame.  It uses the function @code{pop-to-buffer} internally (see
below).

If the specified buffer is already displayed in another window, in any
frame on the current terminal, this switches to that window instead of
creating a new frame.  However, the selected window is never used for
this.

The @var{buffer-or-name} and @var{norecord} arguments have the same
meanings as in @code{switch-to-buffer}.
@end deffn

The above commands use the function @code{pop-to-buffer}, which
flexibly displays a buffer in some window and selects that window for
editing.  In turn, @code{pop-to-buffer} uses @code{display-buffer} for
displaying the buffer.  Hence, all the variables affecting
@code{display-buffer} will affect it as well.  @xref{Choosing Window},
for the documentation of @code{display-buffer}.

@deffn Command pop-to-buffer buffer-or-name &optional action norecord
This function makes @var{buffer-or-name} the current buffer and
displays it in some window, preferably not the window currently
selected.  It then selects the displaying window.  If that window is
on a different graphical frame, that frame is given input focus if
possible (@pxref{Input Focus}).

If @var{buffer-or-name} is @code{nil}, it defaults to the buffer
returned by @code{other-buffer} (@pxref{Buffer List}).  If
@var{buffer-or-name} is a string that is not the name of any existing
buffer, this function creates a new buffer with that name; the new
buffer's major mode is determined by the variable @code{major-mode}
(@pxref{Major Modes}).  In any case, that buffer is made current and
returned, even when no suitable window was found to display it.

If @var{action} is non-@code{nil}, it should be a display action to
pass to @code{display-buffer} (@pxref{Choosing Window}).
Alternatively, a non-@code{nil}, non-list value means to pop to a
window other than the selected one---even if the buffer is already
displayed in the selected window.

Like @code{switch-to-buffer}, this function updates the buffer list
unless @var{norecord} is non-@code{nil}.
@end deffn


@node Displaying Buffers
@section Displaying a Buffer in a Suitable Window
@cindex buffer display
@cindex displaying a buffer

This section describes lower-level functions Emacs uses to find or
create a window for displaying a specified buffer.  The common
workhorse of these functions is @code{display-buffer} which eventually
handles all incoming requests for buffer display (@pxref{Choosing
Window}).

   @code{display-buffer} delegates the task of finding a suitable
window to so-called action functions (@pxref{Buffer Display Action
Functions}).  First, @code{display-buffer} compiles a so-called action
alist---a special association list that action functions can use to
fine-tune their behavior.  Then it passes that alist on to each action
function it calls (@pxref{Buffer Display Action Alists}).

   The behavior of @code{display-buffer} is highly customizable.  To
understand how customizations are used in practice, you may wish to
study examples illustrating the order of precedence which
@code{display-buffer} uses to call action functions (@pxref{Precedence
of Action Functions}).  To avoid conflicts between Lisp programs
calling @code{display-buffer} and user customizations of its behavior,
it may make sense to follow a number of guidelines which are sketched
in the final part of this section (@pxref{The Zen of Buffer Display}).

@menu
* Choosing Window::         How to choose a window for displaying a buffer.
* Buffer Display Action Functions:: Support functions for buffer display.
* Buffer Display Action Alists:: Alists for fine-tuning buffer display.
* Choosing Window Options:: Extra options affecting how buffers are displayed.
* Precedence of Action Functions:: Examples to explain the precedence of
                              action functions.
* The Zen of Buffer Display:: How to avoid that buffers get lost in between
                              windows.
@end menu


@node Choosing Window
@subsection Choosing a Window for Displaying a Buffer

The command @code{display-buffer} flexibly chooses a window for
display, and displays a specified buffer in that window.  It can be
called interactively, via the key binding @kbd{C-x 4 C-o}.  It is also
used as a subroutine by many functions and commands, including
@code{switch-to-buffer} and @code{pop-to-buffer} (@pxref{Switching
Buffers}).

@cindex buffer display display action
@cindex display action
  This command performs several complex steps to find a window to
display in.  These steps are described by means of @dfn{display
actions}, which have the form @code{(@var{functions} . @var{alist})}.
Here, @var{functions} is either a single function or a list of
functions, referred to as ``action functions'' (@pxref{Buffer Display
Action Functions}); and @var{alist} is an association list, referred
to as ``action alist'' (@pxref{Buffer Display Action Alists}).
@xref{The Zen of Buffer Display}, for samples of display actions.

  An action function accepts two arguments: the buffer to display and
an action alist.  It attempts to display the buffer in some window,
picking or creating a window according to its own criteria.  If
successful, it returns the window; otherwise, it returns @code{nil}.

  @code{display-buffer} works by combining display actions from
several sources, and calling the action functions in turn, until one
of them manages to display the buffer and returns a non-@code{nil}
value.

@deffn Command display-buffer buffer-or-name &optional action frame
This command makes @var{buffer-or-name} appear in some window, without
selecting the window or making the buffer current.  The argument
@var{buffer-or-name} must be a buffer or the name of an existing
buffer.  The return value is the window chosen to display the buffer,
or @code{nil} if no suitable window was found.

The optional argument @var{action}, if non-@code{nil}, should normally
be a display action (described above).  @code{display-buffer} builds a
list of action functions and an action alist, by consolidating display
actions from the following sources (in order of their precedence,
from highest to lowest):

@itemize
@item
The variable @code{display-buffer-overriding-action}.

@item
The user option @code{display-buffer-alist}.

@item
The @var{action} argument.

@item
The user option @code{display-buffer-base-action}.

@item
The constant @code{display-buffer-fallback-action}.
@end itemize

@noindent
In practice this means that @code{display-buffer} builds a list of all
action functions specified by these display actions.  The first
element of this list is the first action function specified by
@code{display-buffer-overriding-action}, if any.  Its last element is
@code{display-buffer-pop-up-frame}---the last action function
specified by @code{display-buffer-fallback-action}.  Duplicates are
not removed from this list---hence one and the same action function
may be called multiple times during one call of @code{display-buffer}.

@code{display-buffer} calls the action functions specified by this
list in turn, passing the buffer as the first argument and the
combined action alist as the second argument, until one of the
functions returns non-@code{nil}.  @xref{Precedence of Action
Functions}, for examples how display actions specified by different
sources are processed by @code{display-buffer}.

Note that the second argument is always the list of @emph{all} action
alist entries specified by the sources named above.  Hence, the first
element of that list is the first action alist entry specified by
@code{display-buffer-overriding-action}, if any.  Its last element is
the last alist entry of @code{display-buffer-base-action}, if any (the
action alist of @code{display-buffer-fallback-action} is empty).

Note also, that the combined action alist may contain duplicate
entries and entries for the same key with different values.  As a
rule, action functions always use the first association of a key they
find.  Hence, the association an action function uses is not
necessarily the association provided by the display action that
specified that action function,

The argument @var{action} can also have a non-@code{nil}, non-list
value.  This has the special meaning that the buffer should be
displayed in a window other than the selected one, even if the
selected window is already displaying it.  If called interactively
with a prefix argument, @var{action} is @code{t}.  Lisp programs
should always supply a list value.

The optional argument @var{frame}, if non-@code{nil}, specifies which
frames to check when deciding whether the buffer is already displayed.
It is equivalent to adding an element @w{@code{(reusable-frames
. @var{frame})}} to the action alist of @var{action} (@pxref{Buffer
Display Action Alists}).  The @var{frame} argument is provided for
compatibility reasons, Lisp programs should not use it.
@end deffn

@defvar display-buffer-overriding-action
The value of this variable should be a display action, which is
treated with the highest priority by @code{display-buffer}.  The
default value is an empty display action, i.e., @w{@code{(nil . nil)}}.
@end defvar

@defopt display-buffer-alist
The value of this option is an alist mapping conditions to display
actions.  Each condition may be either a regular expression matching a
buffer name or a function that takes two arguments: a buffer name and
the @var{action} argument passed to @code{display-buffer}.  If either
the name of the buffer passed to @code{display-buffer} matches a
regular expression in this alist, or the function specified by a
condition returns non-@code{nil}, then @code{display-buffer} uses the
corresponding display action to display the buffer.
@end defopt

@defopt display-buffer-base-action
The value of this option should be a display action.  This option can
be used to define a standard display action for calls to
@code{display-buffer}.
@end defopt

@defvr Constant display-buffer-fallback-action
This display action specifies the fallback behavior for
@code{display-buffer} if no other display actions are given.
@end defvr


@node Buffer Display Action Functions
@subsection Action Functions for Buffer Display
@cindex buffer display action function
@cindex action function, for buffer display

An @dfn{action function} is a function @code{display-buffer} calls for
choosing a window to display a buffer.  Action functions take two
arguments: @var{buffer}, the buffer to display, and @var{alist}, an
action alist (@pxref{Buffer Display Action Alists}).  They are
supposed to return a window displaying @var{buffer} if they succeed
and @code{nil} if they fail.

   The following basic action functions are defined in Emacs.

@defun display-buffer-same-window buffer alist
This function tries to display @var{buffer} in the selected window.
It fails if the selected window is a minibuffer window or is dedicated
to another buffer (@pxref{Dedicated Windows}).  It also fails if
@var{alist} has a non-@code{nil} @code{inhibit-same-window} entry.
@end defun

@defun display-buffer-reuse-window buffer alist
This function tries to display @var{buffer} by finding a window that
is already displaying it.  Windows on the selected frame are preferred
to windows on other frames.

If @var{alist} has a non-@code{nil} @code{inhibit-same-window} entry,
the selected window is not eligible for reuse.  The set of frames to
search for a window already displaying @var{buffer} can be specified
with the help of the @code{reusable-frames} action alist entry.  If
@var{alist} contains no @code{reusable-frames} entry, this function
searches just the selected frame.

If this function chooses a window on another frame, it makes that
frame visible and, unless @var{alist} contains an
@code{inhibit-switch-frame} entry, raises that frame if necessary.
@end defun

@defun display-buffer-reuse-mode-window buffer alist
This function tries to display @var{buffer} by finding a window
that is displaying a buffer in a given mode.

If @var{alist} contains a @code{mode} entry, its value specifes a
major mode (a symbol) or a list of major modes.  If @var{alist}
contains no @code{mode} entry, the current major mode of @var{buffer}
is used instead.  A window is a candidate if it displays a buffer
whose mode derives from one of the modes specified thusly.

The behavior is also controlled by @var{alist} entries for
@code{inhibit-same-window}, @code{reusable-frames} and
@code{inhibit-switch-frame}, like @code{display-buffer-reuse-window}
does.
@end defun

@defun display-buffer-pop-up-window buffer alist
This function tries to display @var{buffer} by splitting the largest
or least recently-used window (usually located on the selected frame).
It actually performs the split by calling the function specified by
@code{split-window-preferred-function} (@pxref{Choosing Window
Options}).

The size of the new window can be adjusted by supplying
@code{window-height} and @code{window-width} entries in @var{alist}.
If @var{alist} contains a @code{preserve-size} entry, Emacs will also
try to preserve the size of the new window during future resize
operations (@pxref{Preserving Window Sizes}).

This function fails if no window can be split.  More often than not,
this happens because no window is large enough to allow splitting.
Setting @code{split-height-threshold} or @code{split-width-threshold}
to lower values may help in this regard.  Splitting also fails when
the selected frame has an @code{unsplittable} frame parameter;
@pxref{Buffer Parameters}.
@end defun

@defun display-buffer-in-previous-window buffer alist
This function tries to display @var{buffer} in a window where it was
displayed previously.

If @var{alist} contains a non-@code{nil} @code{inhibit-same-window}
entry, the selected window is not eligible for use.  A dedicated
window is usable only if it already shows @var{buffer}.  If
@var{alist} contains a @code{previous-window} entry, the window
specified by that entry is usable even if it never showed @var{buffer}
before.

If @var{alist} contains a @code{reusable-frames} entry (@pxref{Buffer
Display Action Alists}), its value determines which frames to search
for a suitable window.  If @var{alist} contains no
@code{reusable-frames} entry, this function searches just the selected
frame if @code{display-buffer-reuse-frames} and @code{pop-up-frames}
are both @code{nil}; it searches all frames on the current terminal if
either of those variables is non-@code{nil}.

If more than one window qualifies as usable according to these rules,
this function makes a choice in the following order of preference:

@itemize @bullet
@item
The window specified by any @code{previous-window} @var{alist} entry,
provided it is not the selected window.

@item
A window that showed @var{buffer} before, provided it is not the
selected window.

@item
The selected window if it is either specified by a
@code{previous-window} @var{alist} entry or showed @var{buffer}
before.
@end itemize
@end defun

@defun display-buffer-use-some-window buffer alist
This function tries to display @var{buffer} by choosing an existing
window and displaying the buffer in that window.  It can fail if all
windows are dedicated to other buffers (@pxref{Dedicated Windows}).
@end defun

@defun display-buffer-in-direction buffer alist
This function tries to display @var{buffer} at a location specified by
@var{alist}.  For this purpose, @var{alist} should contain a
@code{direction} entry whose value is one of @code{left}, @code{above}
(or @code{up}), @code{right} and @code{below} (or @code{down}).  Other
values are usually interpreted as @code{below}.

If @var{alist} also contains a @code{window} entry, its value
specifies a reference window.  That value can be a special symbol like
@code{main} which stands for the selected frame's main window
(@pxref{Side Window Options and Functions}) or @code{root} standing
for the selected frame's root window (@pxref{Windows and Frames}).  It
can also specify an arbitrary valid window.  Any other value (or
omitting the @code{window} entry entirely) means to use the selected
window as reference window.

This function first tries to reuse a window in the specified direction
that already shows @var{buffer}.  If no such window exists, it tries
to split the reference window in order to produce a new window in the
specified direction.  If this fails as well, it will try to display
@var{buffer} in an existing window in the specified direction.  In
either case, the window chosen will appear on the side of the
reference window specified by the @code{direction} entry, sharing at
least one edge with the reference window.

If the reference window is live, the edge the chosen window will share
with it is always the opposite of the one specified by the
@code{direction} entry.  For example, if the value of the
@code{direction} entry is @code{left}, the chosen window's right edge
coordinate (@pxref{Coordinates and Windows}) will equal the reference
window's left edge coordinate.

If the reference window is internal, a reused window must share with
it the edge specified by the @code{direction} entry.  Hence if, for
example, the reference window is the frame's root window and the value
of the @code{direction} entry is @code{left}, a reused window must be
on the left of the frame.  This means that the left edge coordinate of
the chosen window and that of the reference window are the same.

A new window, however, will be created by splitting the reference
window such that the chosen window will share the opposite edge with
the reference window.  In our example, a new root window would be
created with a new live window and the reference window as its
children.  The chosen window's right edge coordinate would then equal
the left edge coordinate of the reference window.  Its left edge
coordinate would equal the left edge coordinate of the frame's new
root window.

Four special values for @code{direction} entries allow to implicitly
specify the selected frame's main window as the reference window:
@code{leftmost}, @code{top}, @code{rightmost} and @code{bottom}.  This
means that instead of, for example, @w{@code{(direction . left)
(window . main)}} one can just specify @w{@code{(direction
. leftmost)}}.  An existing @code{window} @var{alist} entry is ignored
in such cases.
@end defun

@defun display-buffer-below-selected buffer alist
This function tries to display @var{buffer} in a window below the
selected window.  If there is a window below the selected one and that
window already displays @var{buffer}, it reuses that window.

If there is no such window, this function tries to create a new window
by splitting the selected one, and displays @var{buffer} there.  It will
also try to adjust that window's size provided @var{alist} contains a
suitable @code{window-height} or @code{window-width} entry, see above.

If splitting the selected window fails and there is a non-dedicated
window below the selected one showing some other buffer, this function
tries to use that window for showing @var{buffer}.

If @var{alist} contains a @code{window-min-height} entry, this
function ensures that the window used is or can become at least as
high as specified by that entry's value.  Note that this is only a
guarantee.  In order to actually resize the window used, @var{alist}
must also provide an appropriate @code{window-height} entry.
@end defun

@defun display-buffer-at-bottom buffer alist
This function tries to display @var{buffer} in a window at the bottom
of the selected frame.

This either tries to split the window at the bottom of the frame or
the frame's root window, or to reuse an existing window at the bottom
of the selected frame.
@end defun

@defun display-buffer-pop-up-frame buffer alist
This function creates a new frame, and displays the buffer in that
frame's window.  It actually performs the frame creation by calling
the function specified in @code{pop-up-frame-function}
(@pxref{Choosing Window Options}).  If @var{alist} contains a
@code{pop-up-frame-parameters} entry, the associated value is added to
the newly created frame's parameters.
@end defun

@defun display-buffer-in-child-frame buffer alist
This function tries to display @var{buffer} in a child frame
(@pxref{Child Frames}) of the selected frame, either reusing an
existing child frame or by making a new one.  If @var{alist} has a
non-@code{nil} @code{child-frame-parameters} entry, the corresponding
value is an alist of frame parameters to give the new frame.  A
@code{parent-frame} parameter specifying the selected frame is
provided by default.  If the child frame should become the child of
another frame, a corresponding entry must be added to @var{alist}.

The appearance of child frames is largely dependent on the parameters
provided via @var{alist}.  It is advisable to use at least ratios to
specify the size (@pxref{Size Parameters}) and the position
(@pxref{Position Parameters}) of the child frame, and to add a
@code{keep-ratio} parameter (@pxref{Frame Interaction Parameters}), in
order to make sure that the child frame remains visible.  For other
parameters that should be considered see @ref{Child Frames}.
@end defun

@defun display-buffer-use-some-frame buffer alist
This function tries to display @var{buffer} by finding a frame that
meets a predicate (by default any frame other than the selected
frame).

If this function chooses a window on another frame, it makes that
frame visible and, unless @var{alist} contains an
@code{inhibit-switch-frame} entry, raises that frame if necessary.

If @var{alist} has a non-@code{nil} @code{frame-predicate} entry, its
value is a function taking one argument (a frame), returning
non-@code{nil} if the frame is a candidate; this function replaces the
default predicate.

If @var{alist} has a non-@code{nil} @code{inhibit-same-window} entry,
the selected window is not used; thus if the selected frame has a
single window, it is not used.
@end defun

@defun display-buffer-no-window buffer alist
If @var{alist} has a non-@code{nil} @code{allow-no-window} entry, then
this function does not display @var{buffer} and returns the symbol
@code{fail}.  This constitutes the only exception to the convention
that an action function returns either @code{nil} or a window showing
@var{buffer}.  If @var{alist} has no such @code{allow-no-window}
entry, this function returns @code{nil}.

If this function returns @code{fail}, @code{display-buffer} will skip
the execution of any further display actions and return @code{nil}
immediately.  If this function returns @code{nil},
@code{display-buffer} will continue with the next display action, if
any.

It is assumed that when a caller of @code{display-buffer} specifies a
non-@code{nil} @code{allow-no-window} entry, it is also able to handle
a @code{nil} return value.
@end defun

Two other action functions are described in their proper
sections---@code{display-buffer-in-side-window} (@pxref{Displaying
Buffers in Side Windows}) and @code{display-buffer-in-atom-window}
(@pxref{Atomic Windows}).


@node Buffer Display Action Alists
@subsection Action Alists for Buffer Display
@cindex buffer display action alist
@cindex action alist for buffer display

An @dfn{action alist} is an association list mapping predefined
symbols recognized by action functions to values these functions are
supposed to interpret accordingly.  In each call,
@code{display-buffer} constructs a new, possibly empty action alist
and passes that entire list on to any action function it calls.

   By design, action functions are free in their interpretation of
action alist entries.  In fact, some entries like
@code{allow-no-window} or @code{previous-window} have a meaning only
for one or a few action functions, and are ignored by the rest.  Other
entries, like @code{inhibit-same-window} or @code{window-parameters},
are supposed to be respected by most action functions, including those
provided by application programs and external packages.

   In the previous subsection we have described in detail how
individual action functions interpret the action alist entries they
care about.  Here we give a reference list of all known action alist
entries according to their symbols, together with their values and
action functions (@pxref{Buffer Display Action Functions}) that
recognize them.  Throughout this list, the terms ``buffer'' will refer
to the buffer @code{display-buffer} is supposed to display, and
``value'' refers to the entry's value.

@table @code
@vindex inhibit-same-window@r{, a buffer display action alist entry}
@item inhibit-same-window
If the value is non-@code{nil}, this signals that the selected window
must not be used for displaying the buffer.  All action functions that
(re-)use an existing window should respect this entry.

@vindex previous-window@r{, a buffer display action alist entry}
@item previous-window
The value must specify a window that may have displayed the buffer
previously.  @code{display-buffer-in-previous-window} will give
preference to such a window provided it is still live and not
dedicated to another buffer.

@vindex mode@r{, a buffer display action alist entry}
@item mode
The value is either a major mode or a list of major modes.
@code{display-buffer-reuse-mode-window} may reuse a window whenever
the value specified by this entry matches the major mode of that
window's buffer.  Other action functions ignore such entries.

@vindex frame-predicate@r{, a buffer display action alist entry}
@item frame-predicate
The value must be a function taking one argument (a frame), supposed
to return non-@code{nil} if that frame is a candidate for displaying
the buffer.  This entry is used by
@code{display-buffer-use-some-frame}.

@vindex reusable-frames@r{, a buffer display action alist entry}
@item reusable-frames
The value specifies the set of frames to search for a window that can
be reused because it already displays the buffer.  It can be set as
follows:

@itemize @bullet
@item
@code{nil} means consider only windows on the selected frame.
(Actually, the last frame used that is not a minibuffer-only frame.)
@item
@code{t} means consider windows on all frames.
@item
@code{visible} means consider windows on all visible frames.
@item
0 means consider windows on all visible or iconified frames.
@item
A frame means consider windows on that frame only.
@end itemize

Note that the meaning of @code{nil} differs slightly from that of the
@var{all-frames} argument to @code{next-window} (@pxref{Cyclic Window
Ordering}).

A major client of this is @code{display-buffer-reuse-window}, but all
other action functions that try to reuse a window are affected as
well.  @code{display-buffer-in-previous-window} consults it when
searching for a window that previously displayed the buffer on another
frame.

@vindex inhibit-switch-frame@r{, a buffer display action alist entry}
@item inhibit-switch-frame
A non-@code{nil} value prevents another frame from being raised or
selected, if the window chosen by @code{display-buffer} is displayed
there.  Primarily affected by this are
@code{display-buffer-use-some-frame} and
@code{display-buffer-reuse-window}.
@code{display-buffer-pop-up-frame} should be affected as well, but
there is no guarantee that the window manager will comply.

@vindex window-parameters@r{, a buffer display action alist entry}
@item window-parameters
The value specifies an alist of window parameters to give the chosen
window.  All action functions that choose a window should process this
entry.

@vindex window-min-height@r{, a buffer display action alist entry}
@item window-min-height
The value specifies a minimum height of the window used, in lines.  If
a window is not or cannot be made as high as specified by this entry,
the window is not considered for use.  The only client of this entry
is presently @code{display-buffer-below-selected}.

Note that providing such an entry alone does not necessarily make the
window as tall as specified by its value.  To actually resize an
existing window or make a new window as tall as specified by that
value, a @code{window-height} entry specifying that value should be
provided as well.  Such a @code{window-height} entry can, however,
specify a completely different value or ask the window height to be
fit to that of its buffer in which case the @code{window-min-height}
entry provides the guaranteed minimum height of the window used.

@vindex window-height@r{, a buffer display action alist entry}
@item window-height
The value specifies whether and how to adjust the height of the chosen
window and can be one of the following:

@itemize @bullet
@item
@code{nil} means to leave the height of the chosen window alone.

@item
An integer number specifies the desired total height of the chosen
window in lines.

@item
A floating-point number specifies the fraction of the chosen window's
desired total height with respect to the total height of its frame's
root window.

@item
If the value specifies a function, that function is called with one
argument---the chosen window.  The function is supposed to adjust the
height of the window; its return value is ignored.  Suitable functions
are @code{shrink-window-if-larger-than-buffer} and
@code{fit-window-to-buffer}, see @ref{Resizing Windows}.
@end itemize

By convention, the height of the chosen window is adjusted only if the
window is part of a vertical combination (@pxref{Windows and Frames})
to avoid changing the height of other, unrelated windows.  Also, this
entry should be processed only under certain conditions which are
specified right below this list.

@vindex window-width@r{, a buffer display action alist entry}
@item window-width
This entry is similar to the @code{window-height} entry described
before, but used to adjust the chosen window's width instead.  The
value can be one of the following:

@itemize @bullet
@item
@code{nil} means to leave the width of the chosen window alone.

@item
An integer specifies the desired total width of the chosen window in
columns.

@item
A floating-point number specifies the fraction of the chosen window's
desired total width with respect to the total width of the frame's
root window.

@item
If the value specifies a function, that function is called with one
argument---the chosen window.  The function is supposed to adjust the
width of the window; its return value is ignored.
@end itemize

By convention, the width of the chosen window is adjusted only if the
window is part of a horizontal combination (@pxref{Windows and
Frames}) to avoid changing the width of other, unrelated windows.
Also, this entry should be processed under only certain conditions
which are specified right below this list.

@vindex dedicated@r{, a buffer display action alist entry}
@item dedicated
If non-@code{nil}, such an entry tells @code{display-buffer} to mark
any window it creates as dedicated to its buffer (@pxref{Dedicated
Windows}).  It does that by calling @code{set-window-dedicated-p} with
the chosen window as first argument and the entry's value as second.

@vindex preserve-size@r{, a buffer display action alist entry}
@item preserve-size
If non-@code{nil} such an entry tells Emacs to preserve the size of
the window chosen (@pxref{Preserving Window Sizes}).  The value should
be either @w{@code{(t . nil)}} to preserve the width of the window,
@w{@code{(nil . t)}} to preserve its height or @w{@code{(t . t)}} to
preserve both, its width and its height.  This entry should be
processed only under certain conditions which are specified right
after this list.

@vindex pop-up-frame-parameters@r{, a buffer display action alist entry}
@item pop-up-frame-parameters
The value specifies an alist of frame parameters to give a new frame,
if one is created.  @code{display-buffer-pop-up-frame} is its one and
only addressee.

@vindex parent-frame@r{, a buffer display action alist entry}
@item parent-frame
The value specifies the parent frame to be used when the buffer is
displayed on a child frame.  This entry is used only by
@code{display-buffer-in-child-frame}.

@vindex child-frame-parameters@r{, a buffer display action alist entry}
@item child-frame-parameters
The value specifies an alist of frame parameters to use when the buffer
is displayed on a child frame.  This entry is used only by
@code{display-buffer-in-child-frame}.

@vindex side@r{, a buffer display action alist entry}
@item side
The value denotes the side of the frame or window where a new window
displaying the buffer shall be created.  This entry is used by
@code{display-buffer-in-side-window} to indicate the side of the frame
where a new side window shall be placed (@pxref{Displaying Buffers in
Side Windows}).  It is also used by
@code{display-buffer-in-atom-window} to indicate the side of an
existing window where the new window shall be located (@pxref{Atomic
Windows}).

@vindex slot@r{, a buffer display action alist entry}
@item slot
If non-@code{nil}, the value specifies the slot of the side window
supposed to display the buffer.  This entry is used only by
@code{display-buffer-in-side-window}.

@vindex direction@r{, a buffer display action alist entry}
@item direction
The value specifies a direction which, together with a @code{window}
entry, allows @code{display-buffer-in-direction} to determine the
location of the window to display the buffer.

@vindex window@r{, a buffer display action alist entry}
@item window
The value specifies a window that is in some way related to the window
chosen by @code{display-buffer}.  This entry is currently used by
@code{display-buffer-in-atom-window} to indicate the window on whose
side the new window shall be created.  It is also used by
@code{display-buffer-in-direction} to specify the reference window on
whose side the resulting window shall appear.

@vindex allow-no-window@r{, a buffer display action alist entry}
@item allow-no-window
If the value is non-@code{nil}, @code{display-buffer} does not
necessarily have to display the buffer and the caller is prepared to
accept that.  This entry is not intended for user customizations,
since there is no guarantee that an arbitrary caller of
@code{display-buffer} will be able to handle the case that no window
will display the buffer.  @code{display-buffer-no-window} is the only
action function that cares about this entry.
@end table

By convention, the entries @code{window-height}, @code{window-width}
and @code{preserve-size} are applied after the chosen window's buffer
has been set up and if and only if that window never showed another
buffer before.  More precisely, the latter means that the window must
have been either created by the current @code{display-buffer} call or
the window was created earlier by @code{display-buffer} to show the
buffer and never was used to show another buffer until it was reused
by the current invocation of @code{display-buffer}.


@node Choosing Window Options
@subsection Additional Options for Displaying Buffers

The behavior of buffer display actions (@pxref{Choosing Window}) can
be further modified by the following user options.

@defopt pop-up-windows
If the value of this variable is non-@code{nil}, @code{display-buffer}
is allowed to split an existing window to make a new window for
displaying in.  This is the default.

This variable is provided for backward compatibility only.  It is
obeyed by @code{display-buffer} via a special mechanism in
@code{display-buffer-fallback-action}, which calls the action function
@code{display-buffer-pop-up-window} (@pxref{Buffer Display Action
Functions}) when the value of this option is non-@code{nil}.  It is
not consulted by @code{display-buffer-pop-up-window} itself, which the
user may specify directly in @code{display-buffer-alist} etc.
@end defopt

@defopt split-window-preferred-function
This variable specifies a function for splitting a window, in order to
make a new window for displaying a buffer.  It is used by the
@code{display-buffer-pop-up-window} action function to actually split
the window.

The value must be a function that takes one argument, a window, and
returns either a new window (which will be used to display the desired
buffer) or @code{nil} (which means the splitting failed).  The default
value is @code{split-window-sensibly}, which is documented next.
@end defopt

@defun split-window-sensibly &optional window
This function tries to split @var{window} and return the newly created
window.  If @var{window} cannot be split, it returns @code{nil}.  If
@var{window} is omitted or @code{nil}, it defaults to the selected
window.

This function obeys the usual rules that determine when a window may
be split (@pxref{Splitting Windows}).  It first tries to split by
placing the new window below, subject to the restriction imposed by
@code{split-height-threshold} (see below), in addition to any other
restrictions.  If that fails, it tries to split by placing the new
window to the right, subject to @code{split-width-threshold} (see
below).  If that also fails, and the window is the only window on its
frame, this function again tries to split and place the new window
below, disregarding @code{split-height-threshold}.  If this fails as
well, this function gives up and returns @code{nil}.
@end defun

@defopt split-height-threshold
This variable specifies whether @code{split-window-sensibly} is
allowed to split the window placing the new window below.  If it is an
integer, that means to split only if the original window has at least
that many lines.  If it is @code{nil}, that means not to split this
way.
@end defopt

@defopt split-width-threshold
This variable specifies whether @code{split-window-sensibly} is
allowed to split the window placing the new window to the right.  If
the value is an integer, that means to split only if the original
window has at least that many columns.  If the value is @code{nil},
that means not to split this way.
@end defopt

@defopt even-window-sizes
This variable, if non-@code{nil}, causes @code{display-buffer} to even
window sizes whenever it reuses an existing window, and that window is
adjacent to the selected one.

If its value is @code{width-only}, sizes are evened only if the reused
window is on the left or right of the selected one and the selected
window is wider than the reused one.  If its value is @code{height-only}
sizes are evened only if the reused window is above or beneath the
selected window and the selected window is higher than the reused one.
Any other non-@code{nil} value means to even sizes in any of these cases
provided the selected window is larger than the reused one in the sense
of their combination.
@end defopt

@defopt pop-up-frames
If the value of this variable is non-@code{nil}, that means
@code{display-buffer} may display buffers by making new frames.  The
default is @code{nil}.

A non-@code{nil} value also means that when @code{display-buffer} is
looking for a window already displaying @var{buffer-or-name}, it can
search any visible or iconified frame, not just the selected frame.

This variable is provided mainly for backward compatibility.  It is
obeyed by @code{display-buffer} via a special mechanism in
@code{display-buffer-fallback-action}, which calls the action function
@code{display-buffer-pop-up-frame} (@pxref{Buffer Display Action
Functions}) if the value is non-@code{nil}.  (This is done before
attempting to split a window.)  This variable is not consulted by
@code{display-buffer-pop-up-frame} itself, which the user may specify
directly in @code{display-buffer-alist} etc.
@end defopt

@defopt pop-up-frame-function
This variable specifies a function for creating a new frame, in order
to make a new window for displaying a buffer.  It is used by the
@code{display-buffer-pop-up-frame} action function.

The value should be a function that takes no arguments and returns a
frame, or @code{nil} if no frame could be created.  The default value
is a function that creates a frame using the parameters specified by
@code{pop-up-frame-alist} (see below).
@end defopt

@defopt pop-up-frame-alist
This variable holds an alist of frame parameters (@pxref{Frame
Parameters}), which is used by the function specified by
@code{pop-up-frame-function} to make a new frame.  The default is
@code{nil}.

This option is provided for backward compatibility only.  Note, that
when @code{display-buffer-pop-up-frame} calls the function specified
by @code{pop-up-frame-function}, it prepends the value of all
@code{pop-up-frame-parameters} action alist entries to
@code{pop-up-frame-alist} so that the values specified by the action
alist entry effectively override any corresponding values of
@code{pop-up-frame-alist}.

Hence, users should set up a @code{pop-up-frame-parameters} action
alist entry in @code{display-buffer-alist} instead of customizing
@code{pop-up-frame-alist}.  Only this will guarantee that the value of
a parameter specified by the user overrides the value of that
parameter specified by the caller of @code{display-buffer}.
@end defopt

   Many efforts in the design of @code{display-buffer} have been given
to maintain compatibility with code that uses older options like
@code{pop-up-windows}, @code{pop-up-frames},
@code{pop-up-frame-alist}, @code{same-window-buffer-names} and
@code{same-window-regexps}.  Lisp Programs and users should refrain
from using these options.  Above we already warned against customizing
@code{pop-up-frame-alist}.  Here we describe how to convert the
remaining options to use display actions instead.

@table @code
@item pop-up-windows
@vindex pop-up-windows@r{, replacement for}
This variable is @code{t} by default.  Instead of customizing it to
@code{nil} and thus telling @code{display-buffer} what not to do, it's
much better to list in @code{display-buffer-base-action} the action
functions it should try instead as, for example:

@example
@group
(customize-set-variable
 'display-buffer-base-action
 '((display-buffer-reuse-window display-buffer-same-window
    display-buffer-in-previous-window
    display-buffer-use-some-window)))
@end group
@end example

@item pop-up-frames
@vindex pop-up-frames@r{, replacement for}
Instead of customizing this variable to @code{t}, customize
@code{display-buffer-base-action}, for example, as follows:

@example
@group
(customize-set-variable
 'display-buffer-base-action
 '((display-buffer-reuse-window display-buffer-pop-up-frame)
   (reusable-frames . 0)))
@end group
@end example

@item same-window-buffer-names
@itemx same-window-regexps
@vindex same-window-buffer-names@r{, replacement for}
@vindex same-window-regexps@r{, replacement for}
Instead of adding a buffer name or a regular expression to one of
these options use a @code{display-buffer-alist} entry for that buffer
specifying the action function @code{display-buffer-same-window}.

@example
@group
(customize-set-variable
 'display-buffer-alist
 (cons '("\\*foo\\*" (display-buffer-same-window))
        display-buffer-alist))
@end group
@end example
@end table


@node Precedence of Action Functions
@subsection Precedence of Action Functions
@cindex precedence of buffer display action functions
@cindex execution order of buffer display action functions
@cindex buffer display action functions, precedence

From the past subsections we already know that @code{display-buffer}
must be supplied with a number of display actions (@pxref{Choosing
Window}) in order to display a buffer.  In a completely uncustomized
Emacs, these actions are specified by
@code{display-buffer-fallback-action} in the following order of
precedence: Reuse a window, pop up a new window on the same frame, use
a window previously showing the buffer, use some window and pop up a
new frame.  (Note that the remaining actions named by
@code{display-buffer-fallback-action} are void in an uncustomized
Emacs).

Consider the following form:

@example
(display-buffer (get-buffer-create "*foo*"))
@end example

@noindent
Evaluating this form in the buffer @file{*scratch*} of an uncustomized
Emacs session will usually fail to reuse a window that shows
@file{*foo*} already, but succeed in popping up a new window.
Evaluating the same form again will now not cause any visible
changes---@code{display-buffer} reused the window already showing
@file{*foo*} because that action was applicable and had the highest
precedence among all applicable actions.

   Popping up a new window will fail if there is not enough space on
the selected frame.  In an uncustomized Emacs it typically fails when
there are already two windows on a frame.  For example, if you now
type @w{@kbd{C-x 1}} followed by @w{@kbd{C-x 2}} and evaluate the form
once more, @file{*foo*} should show up in the lower
window---@code{display-buffer} just used ``some'' window.  If, before
typing @w{@kbd{C-x 2}} you had typed @w{@kbd{C-x o}}, @file{*foo*}
would have been shown in the upper window because ``some'' window
stands for the ``least recently used'' window and the selected window
has been least recently used if and only if it is alone on its frame.

   Let's assume you did not type @w{@kbd{C-x o}} and @file{*foo*} is
shown in the lower window.  Type @w{@kbd{C-x o}} to get there followed
by @w{@kbd{C-x left}} and evaluate the form again.  This should
display @file{*foo*} in the same, lower window because that window had
already shown @file{*foo*} previously and was therefore chosen instead
of some other window.

  So far we have only observed the default behavior in an uncustomized
Emacs session.  To see how this behavior can be customized, let's
consider the option @code{display-buffer-base-action}.  It provides a
very coarse customization which conceptually affects the display of
@emph{any} buffer.  It can be used to supplement the actions supplied
by @code{display-buffer-fallback-action} by reordering them or by
adding actions that are not present there but fit more closely the
user's editing practice.   However, it can also be used to change the
default behavior in a more profound way.

   Let's consider a user who, as a rule, prefers to display buffers on
another frame.  Such a user might provide the following customization:

@example
@group
(customize-set-variable
 'display-buffer-base-action
 '((display-buffer-reuse-window display-buffer-pop-up-frame)
   (reusable-frames . 0)))
@end group
@end example

@noindent
This setting will cause @code{display-buffer} to first try to find a
window showing the buffer on a visible or iconified frame and, if no
such frame exists, pop up a new frame.  You can observe this behavior
on a graphical system by typing @w{@kbd{C-x 1}} in the window showing
@file{*scratch*} and evaluating our canonical @code{display-buffer}
form.  This will usually create (and give focus to) a new frame whose
root window shows @file{*foo*}.  Iconify that frame and evaluate the
canonical form again: @code{display-buffer} will reuse the window on
the new frame (usually raising the frame and giving it focus too).

   Only if creating a new frame fails, @code{display-buffer} will
apply the actions supplied by @code{display-buffer-fallback-action}
which means to again try reusing a window, popping up a new window and
so on.  A trivial way to make frame creation fail is supplied by the
following form:

@example
@group
(let ((pop-up-frame-function 'ignore))
  (display-buffer (get-buffer-create "*foo*")))
@end group
@end example

@noindent
We will forget about that form immediately after observing that it
fails to create a new frame and uses a fallback action instead.

   Note that @code{display-buffer-reuse-window} appears redundant in
the customization of @code{display-buffer-base-action} because it is
already part of @code{display-buffer-fallback-action} and should be
tried there anyway.  However, that would fail because due to the
precedence of @code{display-buffer-base-action} over
@code{display-buffer-fallback-action}, at that time
@code{display-buffer-pop-up-frame} would have already won the race.
In fact, this:

@example
@group
(customize-set-variable
 'display-buffer-base-action
 '(display-buffer-pop-up-frame (reusable-frames . 0)))
@end group
@end example

@noindent
would cause @code{display-buffer} to @emph{always} pop up a new frame
which is probably not what our user wants.

   So far, we have only shown how @emph{users} can customize the
default behavior of @code{display-buffer}.  Let us now see how
@emph{applications} can change the course of @code{display-buffer}.
The canonical way to do that is to use the @var{action} argument of
@code{display-buffer} or a function that calls it, like, for example,
@code{pop-to-buffer} (@pxref{Switching Buffers}).

   Suppose an application wants to display @file{*foo*} preferably
below the selected window (to immediately attract the attention of the
user to the new window) or, if that fails, in a window at the bottom
of the frame.  It could do that with a call like this:

@example
@group
(display-buffer
 (get-buffer-create "*foo*")
 '((display-buffer-below-selected display-buffer-at-bottom)))
@end group
@end example

@noindent
In order to see how this new, modified form works, delete any frame
showing @file{*foo*}, type @w{@kbd{C-x 1}} followed by @w{@kbd{C-x 2}} in the
window showing @file{*scratch*}, and subsequently evaluate that form.
@code{display-buffer} should split the upper window, and show
@file{*foo*} in the new window.  Alternatively, if after @w{@kbd{C-x 2}}
you had typed @w{@kbd{C-x o}}, @code{display-buffer} would have split the
window at the bottom instead.

   Suppose now that, before evaluating the new form, you have made the
selected window as small as possible, for example, by evaluating the
form @code{(fit-window-to-buffer)} in that window.  In that case,
@code{display-buffer} would have failed to split the selected window
and would have split the frame's root window instead, effectively
displaying @file{*foo*} at the bottom of the frame.

   In either case, evaluating the new form a second time should reuse
the window already showing @file{*foo*} since both functions supplied
by the @var{action} argument try to reuse such a window first.

   By setting the @var{action} argument, an application effectively
overrules any customization of @code{display-buffer-base-action}.  Our
user can now either accept the choice of the application, or redouble
by customizing the option @code{display-buffer-alist} as follows:

@example
@group
(customize-set-variable
 'display-buffer-alist
 '(("\\*foo\\*"
    (display-buffer-reuse-window display-buffer-pop-up-frame))))
@end group
@end example

@noindent
Trying this with the new, modified form above in a configuration that
does not show @file{*foo*} anywhere, will display @file{*foo*} on a
separate frame, completely ignoring the @var{action} argument of
@code{display-buffer}.

   Note that we didn't care to specify a @code{reusable-frames} action
alist entry in our specification of @code{display-buffer-alist}.
@code{display-buffer} always takes the first one it finds---in our
case the one specified by @code{display-buffer-base-action}.  If we
wanted to use a different specification, for example, to exclude
iconified frames showing @file{*foo*} from the list of reusable ones,
we would have to specify that separately, however:

@example
@group
(customize-set-variable
 'display-buffer-alist
 '(("\\*foo\\*"
    (display-buffer-reuse-window display-buffer-pop-up-frame)
    (reusable-frames . visible))))
@end group
@end example

@noindent
If you try this, you will notice that repeated attempts to display
@file{*foo*} will succeed to reuse a frame only if that frame is
visible.

   The above example would allow the conclusion that users customize
@code{display-buffer-alist} for the sole purpose to overrule the
@var{action} argument chosen by applications.  Such a conclusion would
be incorrect.  @code{display-buffer-alist} is the standard option for
users to direct the course of display of specific buffers in a
preferred way regardless of whether the display is also guided by an
@var{action} argument.

   We can, however, reasonably conclude that customizing
@code{display-buffer-alist} differs from customizing
@code{display-buffer-base-action} in two major aspects: it is stronger
because it overrides the @var{action} argument of
@code{display-buffer}, and it allows to explicitly specify the
affected buffers.  In fact, displaying other buffers is not affected
in any way by a customization for @file{*foo*}.  For example,

@example
(display-buffer (get-buffer-create "*bar*"))
@end example

@noindent
continues being governed by the settings of
@code{display-buffer-base-action} and
@code{display-buffer-fallback-action} only.

   We could stop with our examples here but Lisp programs still have
an ace up their sleeves which they can use to overrule any
customization of @code{display-buffer-alist}.  It's the variable
@code{display-buffer-overriding-action} which they can bind around
@code{display-buffer} calls as follows:

@example
@group
(let ((display-buffer-overriding-action
       '((display-buffer-same-window))))
  (display-buffer
   (get-buffer-create "*foo*")
   '((display-buffer-below-selected display-buffer-at-bottom))))
@end group
@end example

@noindent
Evaluating this form will usually display @file{*foo*} in the selected
window regardless of the @var{action} argument and any user
customizations.  (Usually, an application will not bother to also
provide an @var{action} argument.  Here it just serves to illustrate
the fact that it gets overridden.)

It might be illustrative to look at the list of action functions
@code{display-buffer} would have tried to display @file{*foo*} with
the customizations we provided here.  The list (including comments
explaining who added this and the subsequent elements) is:

@example
@group
(display-buffer-same-window  ;; `display-buffer-overriding-action'
 display-buffer-reuse-window ;; `display-buffer-alist'
 display-buffer-pop-up-frame
 display-buffer-below-selected ;; ACTION argument
 display-buffer-at-bottom
 display-buffer-reuse-window ;; `display-buffer-base-action'
 display-buffer-pop-up-frame
 display-buffer--maybe-same-window ;; `display-buffer-fallback-action'
 display-buffer-reuse-window
 display-buffer--maybe-pop-up-frame-or-window
 display-buffer-in-previous-window
 display-buffer-use-some-window
 display-buffer-pop-up-frame)
@end group
@end example

@noindent
Note that among the internal functions listed here,
@code{display-buffer--maybe-same-window} is effectively ignored while
@code{display-buffer--maybe-pop-up-frame-or-window} actually runs
@code{display-buffer-pop-up-window}.

The action alist passed in each function call is:

@example
@group
((reusable-frames . visible)
 (reusable-frames . 0))
@end group
@end example

@noindent
which shows that we have used the second specification of
@code{display-buffer-alist} above, overriding the specification
supplied by @code{display-buffer-base-action}.  Suppose our user had
written that as

@example
@group
(customize-set-variable
 'display-buffer-alist
 '(("\\*foo\\*"
    (display-buffer-reuse-window display-buffer-pop-up-frame)
    (inhibit-same-window . t)
    (reusable-frames . visible))))
@end group
@end example

@noindent
In this case the @code{inhibit-same-window} alist entry will
successfully invalidate the @code{display-buffer-same-window}
specification from @code{display-buffer-overriding-action} and
@code{display-buffer} will show @file{*foo*} on another frame.  To
make @code{display-buffer-overriding-action} more robust in this
regard, the application would have to specify an appropriate
@code{inhibit-same-window} entry too, for example, as follows:

@example
@group
(let ((display-buffer-overriding-action
       '(display-buffer-same-window (inhibit-same-window . nil))))
  (display-buffer (get-buffer-create "*foo*")))
@end group
@end example

@noindent
This last example shows that while the precedence order of action
functions is fixed, as described in @ref{Choosing Window}, an action
alist entry specified by a display action ranked lower in that order
can affect the execution of a higher ranked display action.


@node The Zen of Buffer Display
@subsection The Zen of Buffer Display
@cindex guidelines for buffer display
@cindex writing buffer display actions
@cindex buffer display conventions

In its most simplistic form, a frame accommodates always one single
window that can be used for displaying a buffer.  As a consequence, it
is always the latest call of @code{display-buffer} that will have
succeeded in placing its buffer there.

   Since working with such a frame is not very practical, Emacs by
default allows for more complex frame layouts controlled by the
default values of the frame size and the @code{split-height-threshold}
and @code{split-width-threshold} options.  Displaying a buffer not yet
shown on a frame then either splits the single window on that frame or
(re-)uses one of its two windows.

   The default behavior is abandoned as soon as the user customizes
one of these thresholds or manually changes the frame's layout.  The
default behavior is also abandoned when calling @code{display-buffer}
with a non-@code{nil} @var{action} argument or the user customizes one
of the options mentioned in the previous subsections.  Mastering
@code{display-buffer} soon may become a frustrating experience due to
the plethora of applicable display actions and the resulting frame
layouts.

   However, refraining from using buffer display functions and falling
back on a split & delete windows metaphor is not a good idea either.
Buffer display functions give Lisp programs and users a framework to
reconcile their different needs; no comparable framework exists for
splitting and deleting windows.  Buffer display functions also allow
to at least partially restore the layout of a frame when removing a
buffer from it later (@pxref{Quitting Windows}).

   Below we will give a number of guidelines to redeem the frustration
mentioned above and thus to avoid literally losing buffers in-between
the windows of a frame.

@table @asis
@item Write display actions without stress
Writing display actions can be a pain because one has to lump together
action functions and action alists in one huge list.  (Historical
reasons prevented us from having @code{display-buffer} support
separate arguments for these.)  It might help to memorize some basic
forms like the ones listed below:

@example
'(nil (inhibit-same-window . t))
@end example

@noindent
specifies an action alist entry only and no action function.  Its sole
purpose is to inhibit a @code{display-buffer-same-window} function
specified elsewhere from showing the buffer in the same window, see
also the last example of the preceding subsection.

@example
'(display-buffer-below-selected)
@end example

@noindent
on the other hand, specifies one action function and an empty action
alist.  To combine the effects of the above two specifications one
would write the form

@example
'(display-buffer-below-selected (inhibit-same-window . t))
@end example

@noindent
to add another action function one would write

@example
@group
'((display-buffer-below-selected display-buffer-at-bottom)
  (inhibit-same-window . t))
@end group
@end example

@noindent
and to add another alist entry one would write

@example
@group
'((display-buffer-below-selected display-buffer-at-bottom)
  (inhibit-same-window . t)
  (window-height . fit-window-to-buffer))
@end group
@end example

@noindent
That last form can be used as @var{action} argument of
@code{display-buffer} in the following way:

@example
@group
(display-buffer
 (get-buffer-create "*foo*")
 '((display-buffer-below-selected display-buffer-at-bottom)
   (inhibit-same-window . t)
   (window-height . fit-window-to-buffer)))
@end group
@end example

@noindent
In a customization of @code{display-buffer-alist} it would be used as
follows:

@example
@group
(customize-set-variable
 'display-buffer-alist
 '(("\\*foo\\*"
    (display-buffer-below-selected display-buffer-at-bottom)
    (inhibit-same-window . t)
    (window-height . fit-window-to-buffer))))
@end group
@end example

@noindent
To add a customization for a second buffer one would then write:

@example
@group
(customize-set-variable
 'display-buffer-alist
 '(("\\*foo\\*"
    (display-buffer-below-selected display-buffer-at-bottom)
    (inhibit-same-window . t)
    (window-height . fit-window-to-buffer))
   ("\\*bar\\*"
    (display-buffer-reuse-window display-buffer-pop-up-frame)
    (reusable-frames . visible))))
@end group
@end example

@item Treat each other with respect
@code{display-buffer-alist} and @code{display-buffer-base-action} are
user options---Lisp programs must never set or rebind them.
@code{display-buffer-overriding-action}, on the other hand, is
reserved for applications---who seldom use that option and if they use
it, then with utmost care.

   Older implementations of @code{display-buffer} frequently caused
users and applications to fight over the settings of user options like
@code{pop-up-frames} and @code{pop-up-windows} (@pxref{Choosing Window
Options}).  This was one major reason for redesigning
@code{display-buffer}---to provide a clear framework specifying what
users and applications should be allowed to do.

   Lisp programs must be prepared that user customizations may
cause buffers to get displayed in an unexpected way.  They should
never assume in their subsequent behavior, that the buffer has been
shown precisely the way they asked for in the @var{action} argument of
@code{display-buffer}.

   Users should not pose too many and too severe restrictions on how
arbitrary buffers get displayed.  Otherwise, they will risk to lose
the characteristics of showing a buffer for a certain purpose.
Suppose a Lisp program has been written to compare different versions
of a buffer in two windows side-by-side.  If the customization of
@code{display-buffer-alist} prescribes that any such buffer should be
always shown in or below the selected window, the program will have a
hard time to set up the desired window configuration via
@code{display-buffer}.

   To specify a preference for showing an arbitrary buffer, users
should customize @code{display-buffer-base-action}.  An example of how
users who prefer working with multiple frames would do that was given
in the previous subsection.  @code{display-buffer-alist} should be
reserved for displaying specific buffers in a specific way.

@item Consider reusing a window that already shows the buffer
Generally, it's always a good idea for users and Lisp
programmers to be prepared for the case that a window already shows
the buffer in question and to reuse that window.  In the preceding
subsection we have shown that failing to do so properly may cause
@code{display-buffer} to continuously pop up a new frame although a
frame showing that buffer existed already.  In a few cases only, it
might be undesirable to reuse a window, for example, when a different
portion of the buffer should be shown in that window.

   Hence, @code{display-buffer-reuse-window} is one action function
that should be used as often as possible, both in @var{action}
arguments and customizations.  An @code{inhibit-same-window} entry in
the @var{action} argument usually takes care of the most common case
where reusing a window showing the buffer should be avoided---that
where the window in question is the selected one.

@item Attract focus to the window chosen
This is a no-brainer for people working with multiple frames---the
frame showing the buffer will automatically raise and get focus unless
an @code{inhibit-switch-frame} entry forbids it.  For single frame
users this task can be considerably more difficult.  In particular,
@code{display-buffer-pop-up-window} and
@code{display-buffer-use-some-window} can become obtrusive in this
regard.  They split or use a seemingly arbitrary (often the largest or
least recently used) window, distracting the user's attention.

Some Lisp programs therefore try to choose a window at the bottom of
the frame, for example, in order to display the buffer in vicinity of
the minibuffer window where the user is expected to answer a question
related to the new window.  For non-input related actions
@code{display-buffer-below-selected} might be preferable because the
selected window usually already has the user's attention.

@item Handle subsequent invocations of @code{display-buffer}
@code{display-buffer} is not overly well suited for displaying several
buffers in sequence and making sure that all these buffers are shown
orderly in the resulting window configuration.  Again, the standard
action functions @code{display-buffer-pop-up-window} and
@code{display-buffer-use-some-window} are not very suited for this
purpose due to their somewhat chaotic nature in more complex
configurations.

   To produce a window configuration displaying multiple buffers (or
different views of one and the same buffer) in one and the same
display cycle, Lisp programmers will unavoidably have to write
their own action functions.  A few tricks listed below might help in
this regard.

@itemize @bullet
@item
Making windows atomic (@pxref{Atomic Windows}) avoids breaking an
existing window composition when popping up a new window.
The new window will pop up outside the composition instead.

@item
Temporarily dedicating windows to their buffers (@pxref{Dedicated
Windows}) avoids using a window for displaying a different
buffer.  A non-dedicated window will be used instead.

@item
Calling @code{window-preserve-size} (@pxref{Preserving Window Sizes})
will try to keep the size of the argument window unchanged when
popping up a new window.  You have to make sure that another window in
the same combination can be shrunk instead, though.

@item
Side windows (@pxref{Side Windows}) can be used for displaying
specific buffers always in a window at the same position of a frame.
This permits grouping buffers that do not compete for being shown at
the same time on a frame and showing any such buffer in the same window
without disrupting the display of other buffers.

@item
Child frames (@pxref{Child Frames}) can be used to display a buffer
within the screen estate of the selected frame without disrupting that
frame's window configuration and without the overhead associated with
full-fledged frames as inflicted by @code{display-buffer-pop-up-frame}.
@end itemize
@end table


@node Window History
@section Window History
@cindex window history

Each window remembers in a list the buffers it has previously
displayed, and the order in which these buffers were removed from it.
This history is used, for example, by @code{replace-buffer-in-windows}
(@pxref{Buffers and Windows}), and when quitting windows
(@pxref{Quitting Windows}).  The list is automatically maintained by
Emacs, but you can use the following functions to explicitly inspect
or alter it:

@defun window-prev-buffers &optional window
This function returns a list specifying the previous contents of
@var{window}.  The optional argument @var{window} should be a live
window and defaults to the selected one.

Each list element has the form @code{(@var{buffer} @var{window-start}
@var{window-pos})}, where @var{buffer} is a buffer previously shown in
the window, @var{window-start} is the window start position
(@pxref{Window Start and End}) when that buffer was last shown, and
@var{window-pos} is the point position (@pxref{Window Point}) when
that buffer was last shown in @var{window}.

The list is ordered so that earlier elements correspond to more
recently-shown buffers, and the first element usually corresponds to the
buffer most recently removed from the window.
@end defun

@defun set-window-prev-buffers window prev-buffers
This function sets @var{window}'s previous buffers to the value of
@var{prev-buffers}.  The argument @var{window} must be a live window
and defaults to the selected one.  The argument @var{prev-buffers}
should be a list of the same form as that returned by
@code{window-prev-buffers}.
@end defun

In addition, each window maintains a list of @dfn{next buffers}, which
is a list of buffers re-shown by @code{switch-to-prev-buffer} (see
below).  This list is mainly used by @code{switch-to-prev-buffer} and
@code{switch-to-next-buffer} for choosing buffers to switch to.

@defun window-next-buffers &optional window
This function returns the list of buffers recently re-shown in
@var{window} via @code{switch-to-prev-buffer}.  The @var{window}
argument must denote a live window or @code{nil} (meaning the selected
window).
@end defun

@defun set-window-next-buffers window next-buffers
This function sets the next buffer list of @var{window} to
@var{next-buffers}.  The @var{window} argument should be a live window
or @code{nil} (meaning the selected window).  The argument
@var{next-buffers} should be a list of buffers.
@end defun

The following commands can be used to cycle through the global buffer
list, much like @code{bury-buffer} and @code{unbury-buffer}.  However,
they cycle according to the specified window's history list, rather
than the global buffer list.  In addition, they restore
window-specific window start and point positions, and may show a
buffer even if it is already shown in another window.  The
@code{switch-to-prev-buffer} command, in particular, is used by
@code{replace-buffer-in-windows}, @code{bury-buffer} and
@code{quit-window} to find a replacement buffer for a window.

@deffn Command switch-to-prev-buffer &optional window bury-or-kill
This command displays the previous buffer in @var{window}.  The
argument @var{window} should be a live window or @code{nil} (meaning
the selected window).  If the optional argument @var{bury-or-kill} is
non-@code{nil}, this means that the buffer currently shown in
@var{window} is about to be buried or killed and consequently should
not be switched to in future invocations of this command.

The previous buffer is usually the buffer shown before the buffer
currently shown in @var{window}.  However, a buffer that has been buried
or killed, or has been already shown by a recent invocation of
@code{switch-to-prev-buffer}, does not qualify as previous buffer.

If repeated invocations of this command have already shown all buffers
previously shown in @var{window}, further invocations will show buffers
from the buffer list of the frame @var{window} appears on (@pxref{Buffer
List}).

The option @code{switch-to-prev-buffer-skip} described below can be
used to inhibit switching to certain buffers, for example, to those
already shown in another window.  Also, if @var{window}'s frame has a
@code{buffer-predicate} parameter (@pxref{Buffer Parameters}), that
predicate may inhibit switching to certain buffers.
@end deffn

@deffn Command switch-to-next-buffer &optional window
This command switches to the next buffer in @var{window}, thus undoing
the effect of the last @code{switch-to-prev-buffer} command in
@var{window}.  The argument @var{window} must be a live window and
defaults to the selected one.

If there is no recent invocation of @code{switch-to-prev-buffer} that
can be undone, this function tries to show a buffer from the buffer list
of the frame @var{window} appears on (@pxref{Buffer List}).

The option @code{switch-to-prev-buffer-skip} and the
@code{buffer-predicate} (@pxref{Buffer Parameters}) of @var{window}'s
frame affect this command as they do for @code{switch-to-prev-buffer}.
@end deffn

By default @code{switch-to-prev-buffer} and
@code{switch-to-next-buffer} can switch to a buffer that is already
shown in another window.  The following option can be used to override
this behavior.

@defopt switch-to-prev-buffer-skip
If this variable is @code{nil}, @code{switch-to-prev-buffer} may
switch to any buffer, including those already shown in other windows.

If this variable is non-@code{nil}, @code{switch-to-prev-buffer} will
refrain from switching to certain buffers.  The following values can
be used:

@itemize @bullet
@item
@code{this} means do not switch to a buffer shown on the frame that
hosts the window @code{switch-to-prev-buffer} is acting upon.

@item
@code{visible} means do not switch to a buffer shown on any visible
frame.

@item
0 (the number zero) means do not switch to a buffer shown on any
visible or iconified frame.

@item
@code{t} means do not switch to a buffer shown on any live frame.

@item
A function that takes three arguments---the @var{window} argument of
@code{switch-to-prev-buffer}, a buffer @code{switch-to-prev-buffer}
intends to switch to and the @var{bury-or-kill} argument of
@code{switch-to-prev-buffer}.  If that function returns
non-@code{nil}, @code{switch-to-prev-buffer} will refrain from
switching to the buffer specified by the second argument.
@end itemize

The command @code{switch-to-next-buffer} obeys this option in a
similar way.  If this option specifies a function,
@code{switch-to-next-buffer} will call that function with the third
argument always @code{nil}.

Note that since @code{switch-to-prev-buffer} is called by
@code{bury-buffer}, @code{replace-buffer-in-windows} and
@code{quit-restore-window} as well, customizing this option may also
affect the behavior of Emacs when a window is quit or a buffer gets
buried or killed.

Note also that under certain circumstances
@code{switch-to-prev-buffer} and @code{switch-to-next-buffer} may
ignore this option, for example, when there is only one buffer left
these functions can switch to.
@end defopt


@node Dedicated Windows
@section Dedicated Windows
@cindex dedicated window

Functions for displaying a buffer can be told to not use specific
windows by marking these windows as @dfn{dedicated} to their buffers.
@code{display-buffer} (@pxref{Choosing Window}) never uses a dedicated
window for displaying another buffer in it.  @code{get-lru-window} and
@code{get-largest-window} (@pxref{Cyclic Window Ordering}) do not
consider dedicated windows as candidates when their @var{dedicated}
argument is non-@code{nil}.  The behavior of @code{set-window-buffer}
(@pxref{Buffers and Windows}) with respect to dedicated windows is
slightly different, see below.

   Functions supposed to remove a buffer from a window or a window from
a frame can behave specially when a window they operate on is dedicated.
We will distinguish three basic cases, namely where (1) the window is
not the only window on its frame, (2) the window is the only window on
its frame but there are other frames on the same terminal left, and (3)
the window is the only window on the only frame on the same terminal.

   In particular, @code{delete-windows-on} (@pxref{Deleting Windows})
handles case (2) by deleting the associated frame and case (3) by
showing another buffer in that frame's only window.  The function
@code{replace-buffer-in-windows} (@pxref{Buffers and Windows}) which is
called when a buffer gets killed, deletes the window in case (1) and
behaves like @code{delete-windows-on} otherwise.
@c FIXME: Does replace-buffer-in-windows _delete_ a window in case (1)?

   When @code{bury-buffer} (@pxref{Buffer List}) operates on the
selected window (which shows the buffer that shall be buried), it
handles case (2) by calling @code{frame-auto-hide-function}
(@pxref{Quitting Windows}) to deal with the selected frame.  The other
two cases are handled as with @code{replace-buffer-in-windows}.

@defun window-dedicated-p &optional window
This function returns non-@code{nil} if @var{window} is dedicated to its
buffer and @code{nil} otherwise.  More precisely, the return value is
the value assigned by the last call of @code{set-window-dedicated-p} for
@var{window}, or @code{nil} if that function was never called with
@var{window} as its argument.  The default for @var{window} is the
selected window.
@end defun

@defun set-window-dedicated-p window flag
This function marks @var{window} as dedicated to its buffer if
@var{flag} is non-@code{nil}, and non-dedicated otherwise.

As a special case, if @var{flag} is @code{t}, @var{window} becomes
@dfn{strongly} dedicated to its buffer.  @code{set-window-buffer}
signals an error when the window it acts upon is strongly dedicated to
its buffer and does not already display the buffer it is asked to
display.  Other functions do not treat @code{t} differently from any
non-@code{nil} value.
@end defun

You can also tell @code{display-buffer} to mark a window it creates as
dedicated to its buffer by providing a suitable @code{dedicated}
action alist entry (@pxref{Buffer Display Action Alists}).

@node Quitting Windows
@section Quitting Windows

When you want to get rid of a window used for displaying a buffer, you
can call @code{delete-window} or @code{delete-windows-on}
(@pxref{Deleting Windows}) to remove that window from its frame.  If the
buffer is shown on a separate frame, you might want to call
@code{delete-frame} (@pxref{Deleting Frames}) instead.  If, on the other
hand, a window has been reused for displaying the buffer, you might
prefer showing the buffer previously shown in that window, by calling the
function @code{switch-to-prev-buffer} (@pxref{Window History}).
Finally, you might want to either bury (@pxref{Buffer List}) or kill
(@pxref{Killing Buffers}) the window's buffer.

   The following command uses information on how the window for
displaying the buffer was obtained in the first place, thus attempting
to automate the above decisions for you.

@deffn Command quit-window &optional kill window
This command quits @var{window} and buries its buffer.  The argument
@var{window} must be a live window and defaults to the selected one.
With prefix argument @var{kill} non-@code{nil}, it kills the buffer
instead of burying it.  It calls the function @code{quit-restore-window}
described next to deal with the window and its buffer.

@vindex quit-window-hook
The functions in @code{quit-window-hook} are run before doing anything
else.
@end deffn

@defun quit-restore-window &optional window bury-or-kill
This function handles @var{window} and its buffer after quitting.  The
optional argument @var{window} must be a live window and defaults to
the selected one. The function's behavior is determined by the four
elements of the list specified by @var{window}'s @code{quit-restore}
parameter (@pxref{Window Parameters}).

The first element of the @code{quit-restore} parameter is one of the
symbols @code{window}, meaning that the window has been specially
created by @code{display-buffer}; @code{frame}, a separate frame has
been created; @code{same}, the window has only ever displayed this
buffer; or @code{other}, the window showed another buffer before.
@code{frame} and @code{window} affect how the window is quit, while
@code{same} and @code{other} affect the redisplay of buffers
previously shown in @var{window}.

The parameter's second element is either one of the symbols
@code{window} or @code{frame}, or a list whose elements are the buffer
shown in @var{window} before, that buffer's window start and window
point positions, and @var{window}'s height at that time.  If that
buffer is still live when @var{window} is quit, then this function may
reuse @var{window} to display it.

The third element is the window selected at the time the parameter was
created.  If this function deletes @var{window}, it subsequently tries
to reselect the window named by that element.

The fourth element is the buffer whose display caused the creation of
this parameter.  This function may delete @var{window} if and only if
it still shows that buffer.

This function will try to delete @var{window} if and only if (1) the
first element of its @code{quit-restore} parameter is either
@code{window} or @code{frame}, (2) the window has no history of
previously-displayed buffers and (3) the fourth element of the
@code{quit-restore} parameter specifies the buffer currently displayed
in @var{window}.  If @var{window} is part of an atomic window
(@pxref{Atomic Windows}), it will try to delete the root of that
atomic window instead.  In either case, it tries to avoid signaling an
error when @var{window} cannot be deleted.

If @var{window} shall be deleted, is the only window on its frame and
there are other frames on that frame's terminal, the value of the
optional argument @var{bury-or-kill} determines how to proceed with
the window.  If @var{bury-or-kill} equals @code{kill}, the frame is
deleted unconditionally.  Otherwise, the fate of the frame is
determined by calling @code{frame-auto-hide-function} (see below) with
that frame as sole argument.

If the third element of the @code{quit-restore} parameter is a list of
buffer, window start (@pxref{Window Start and End}), and point
(@pxref{Window Point}), and that buffer is still live, the buffer will
be displayed, and start and point set accordingly.  If, in addition,
@var{window}'s buffer was temporarily resized, this function will also
try to restore the original height of @var{window}.

Otherwise, if @var{window} was previously used for displaying other
buffers (@pxref{Window History}), the most recent buffer in that
history will be displayed.  In either case, if @var{window} is not
deleted, its @code{quit-restore} parameter is reset to @code{nil}.

The optional argument @var{bury-or-kill} specifies how to deal with
@var{window}'s buffer.  The following values are handled:

@table @code
@item nil
This means to not deal with the buffer in any particular way.  As a
consequence, if @var{window} is not deleted, invoking
@code{switch-to-prev-buffer} will usually show the buffer again.

@item append
This means that if @var{window} is not deleted, its buffer is moved to
the end of @var{window}'s list of previous buffers, so it's less likely
that a future invocation of @code{switch-to-prev-buffer} will switch to
it.  Also, it moves the buffer to the end of the frame's buffer list.

@item bury
This means that if @var{window} is not deleted, its buffer is removed
from @var{window}'s list of previous buffers.  Also, it moves the buffer
to the end of the frame's buffer list.  This value provides the most
reliable remedy to not have @code{switch-to-prev-buffer} switch to this
buffer again without killing the buffer.

@item kill
This means to kill @var{window}'s buffer.
@end table

Typically, the display routines run by @code{display-buffer} will set
the @code{quit-restore} window parameter correctly.  It's also
possible to set it manually, using the following code for displaying
@var{buffer} in @var{window}:

@example
@group
(display-buffer-record-window type window buffer)

(set-window-buffer window buffer)

(set-window-prev-buffers window nil)
@end group
@end example

Setting the window history to @code{nil} ensures that a future call to
@code{quit-window} can delete the window altogether.

@end defun

The following option specifies how to deal with a frame containing just
one window that should be either quit, or whose buffer should be buried.

@defopt frame-auto-hide-function
The function specified by this option is called to automatically hide
frames.  This function is called with one argument---a frame.

The function specified here is called by @code{bury-buffer}
(@pxref{Buffer List}) when the selected window is dedicated and shows
the buffer to bury.  It is also called by @code{quit-restore-window}
(see above) when the frame of the window to quit has been specially
created for displaying that window's buffer and the buffer is not
killed.

The default is to call @code{iconify-frame} (@pxref{Visibility of
Frames}).  Alternatively, you may specify either @code{delete-frame}
(@pxref{Deleting Frames}) to remove the frame from its display,
@code{make-frame-invisible} to make the frame invisible, @code{ignore}
to leave the frame unchanged, or any other function that can take a
frame as its sole argument.

Note that the function specified by this option is called only if the
specified frame contains just one live window and there is at least one
other frame on the same terminal.

For a particular frame, the value specified here may be overridden by
that frame's @code{auto-hide-function} frame parameter (@pxref{Frame
Interaction Parameters}).
@end defopt


@node Side Windows
@section Side Windows
@cindex side windows
@cindex main window
@cindex main window of a frame

Side windows are special windows positioned at any of the four sides of
a frame's root window (@pxref{Windows and Frames}).  In practice, this
means that the area of the frame's root window is subdivided into a main
window and a number of side windows surrounding that main window.  The
main window is either a ``normal'' live window or specifies the area
containing all the normal windows.

   In their most simple form of use, side windows allow to display
specific buffers always in the same area of a frame.  Hence they can
be regarded as a generalization of the concept provided by
@code{display-buffer-at-bottom} (@pxref{Buffer Display Action
Functions}) to the remaining sides of a frame.  With suitable
customizations, however, side windows can be also used to provide
frame layouts similar to those found in so-called integrated
development environments (IDEs).

@menu
* Displaying Buffers in Side Windows:: An action function for displaying
                              buffers in side windows.
* Side Window Options and Functions:: Further tuning of side windows.
* Frame Layouts with Side Windows:: Setting up frame layouts with side
                              windows.
@end menu


@node Displaying Buffers in Side Windows
@subsection Displaying Buffers in Side Windows

The following action function for @code{display-buffer} (@pxref{Buffer
Display Action Functions}) creates or reuses a side window for
displaying the specified buffer.

@defun display-buffer-in-side-window buffer alist
This function displays @var{buffer} in a side window of the selected
frame.  It returns the window used for displaying @var{buffer},
@code{nil} if no such window can be found or created.

@var{alist} is an association list of symbols and values as for
@code{display-buffer}.  The following symbols in @var{alist} are special
for this function:

@table @code
@item side
Denotes the side of the frame where the window shall be located.  Valid
values are @code{left}, @code{top}, @code{right} and @code{bottom}.  If
unspecified, the window is located at the bottom of the frame.

@item slot
Denotes a slot at the specified side where to locate the window.  A
value of zero means to preferably position the window in the middle of
the specified side.  A negative value means to use a slot preceding
(that is, above or on the left of) the middle slot.  A positive value
means to use a slot following (that is, below or on the right of) the
middle slot.  Hence, all windows on a specific side are ordered by their
@code{slot} value.  If unspecified, the window is located in the middle
of the specified side.
@end table

If you specify the same slot on the same side for two or more different
buffers, the buffer displayed last is shown in the corresponding window.
Hence, slots can be used for sharing the same side window between
buffers.

This function installs the @code{window-side} and @code{window-slot}
parameters (@pxref{Window Parameters}) and makes them persistent.  It
does not install any other window parameters unless they have been
explicitly provided via a @code{window-parameters} entry in @var{alist}.
@end defun

By default, side windows cannot be split via @code{split-window}
(@pxref{Splitting Windows}).  Also, a side window is not reused or
split by any buffer display action (@pxref{Buffer Display Action
Functions}) unless it is explicitly specified as target of that
action.  Note also that @code{delete-other-windows} cannot make a side
window the only window on its frame (@pxref{Deleting Windows}).

   Once set up, side windows also change the behavior of the commands
@code{switch-to-prev-buffer} and @code{switch-to-next-buffer}
(@pxref{Window History}).  In particular, these commands will refrain
from showing, in a side window, buffers that have not been displayed in
that window before.  They will also refrain from having a normal,
non-side window show a buffer that has been already displayed in a side
window.  A notable exception to the latter rule occurs when an
application, after displaying a buffer, resets that buffer's local
variables.


@node Side Window Options and Functions
@subsection Side Window Options and Functions

The following options provide additional control over the placement of
side windows.

@defopt window-sides-vertical
If non-@code{nil}, the side windows on the left and right of a frame
occupy the frame's full height.  Otherwise, the side windows on the top
and bottom of the frame occupy the frame's full width.
@end defopt

@defopt window-sides-slots
This option specifies the maximum number of side windows on each side of
a frame.  The value is a list of four elements specifying the number of
side window slots on (in this order) the left, top, right and bottom of
each frame.  If an element is a number, it means to display at most that
many windows on the corresponding side.  If an element is @code{nil}, it
means there's no bound on the number of slots on that side.

If any of the specified values is zero, no window can be created on the
corresponding side.  @code{display-buffer-in-side-window} will not
signal an error in that case, but will return @code{nil}.  If a specified
value just forbids the creation of an additional side window, the most
suitable window on that side is reused and may have its
@code{window-slot} parameter changed accordingly.
@end defopt

@defopt window-sides-reversed
This option specifies whether top/bottom side windows should appear in
reverse order.  When this is @code{nil}, side windows on the top and
bottom of a frame are always drawn from left to right with increasing
slot values.  When this is @code{t}, the drawing order is reversed and
side windows on the top and bottom of a frame are drawn from right to
left with increasing slot values.

When this is @code{bidi}, the drawing order is reversed if and only if
the value of @code{bidi-paragraph-direction} (@pxref{Bidirectional
Display}) is @code{right-to-left} in the buffer displayed in the window
most recently selected within the main window area of this frame.
Sometimes that window may be hard to find, so heuristics are used to
avoid that the drawing order changes inadvertently when another window
gets selected.

The layout of side windows on the left or right of a frame is not
affected by the value of this variable.
@end defopt

When a frame has side windows, the following function returns the main
window of that frame.

@defun window-main-window &optional frame
This function returns the main window of the specified @var{frame}.  The
optional argument @var{frame} must be a live frame and defaults to the
selected one.

If @var{frame} has no side windows, it returns @var{frame}'s root
window.  Otherwise, it returns either an internal non-side window such
that all other non-side windows on @var{frame} descend from it, or the
single live non-side window of @var{frame}.  Note that the main window
of a frame cannot be deleted via @code{delete-window}.
@end defun

The following command is handy to toggle the appearance of all side
windows on a specified frame.

@deffn Command window-toggle-side-windows &optional frame
This command toggles side windows on the specified @var{frame}.  The
optional argument @var{frame} must be a live frame and defaults to the
selected one.

If @var{frame} has at least one side window, this command saves the
state of @var{frame}'s root window in the @var{frame}'s
@code{window-state} frame parameter and deletes all side windows on
@var{frame} afterwards.

If @var{frame} has no side windows, but does have a @code{window-state}
parameter, this command uses that parameter's value to restore the side
windows on @var{frame} leaving @var{frame}'s main window alone.

An error is signaled if @var{frame} has no side windows and no saved
state is found for it.
@end deffn


@node Frame Layouts with Side Windows
@subsection Frame Layouts with Side Windows

Side windows can be used to create more complex frame layouts like those
provided by integrated development environments (IDEs).  In such
layouts, the area of the main window is where the normal editing
activities take place.  Side windows are not conceived for editing in
the usual sense.  Rather, they are supposed to display information
complementary to the current editing activity, like lists of files, tags
or buffers, help information, search or grep results or shell output.

   The layout of such a frame might appear as follows:

@smallexample
@group
     ___________________________________
    |          *Buffer List*            |
    |___________________________________|
    |     |                       |     |
    |  *  |                       |  *  |
    |  d  |                       |  T  |
    |  i  |                       |  a  |
    |  r  |   Main Window Area    |  g  |
    |  e  |                       |  s  |
    |  d  |                       |  *  |
    |  *  |                       |     |
    |_____|_______________________|_____|
    | *help*/*grep*/  |  *shell*/       |
    | *Completions*   |  *compilation*  |
    |_________________|_________________|
    |             Echo Area             |
    |___________________________________|


@end group
@end smallexample

The following example illustrates how window parameters (@pxref{Window
Parameters}) can be used with @code{display-buffer-in-side-window}
(@pxref{Displaying Buffers in Side Windows}) to set up code for
producing the frame layout sketched above.

@example
@group
(defvar parameters
  '(window-parameters . ((no-other-window . t)
                         (no-delete-other-windows . t))))

(setq fit-window-to-buffer-horizontally t)
(setq window-resize-pixelwise t)

(setq
 display-buffer-alist
 `(("\\*Buffer List\\*" display-buffer-in-side-window
    (side . top) (slot . 0) (window-height . fit-window-to-buffer)
    (preserve-size . (nil . t)) ,parameters)
   ("\\*Tags List\\*" display-buffer-in-side-window
    (side . right) (slot . 0) (window-width . fit-window-to-buffer)
    (preserve-size . (t . nil)) ,parameters)
   ("\\*\\(?:help\\|grep\\|Completions\\)\\*"
    display-buffer-in-side-window
    (side . bottom) (slot . -1) (preserve-size . (nil . t))
    ,parameters)
   ("\\*\\(?:shell\\|compilation\\)\\*" display-buffer-in-side-window
    (side . bottom) (slot . 1) (preserve-size . (nil . t))
    ,parameters)))
@end group
@end example

This specifies @code{display-buffer-alist} entries (@pxref{Choosing
Window}) for buffers with fixed names.  In particular, it asks for
showing @file{*Buffer List*} with adjustable height at the top of the
frame and @file{*Tags List*} with adjustable width on the frame's right.
It also asks for having the @file{*help*}, @file{*grep*} and
@file{*Completions*} buffers share a window on the bottom left side of
the frame and the @file{*shell*} and @file{*compilation*} buffers appear
in a window on the bottom right side of the frame.

   Note that the option @code{fit-window-to-buffer-horizontally} must
have a non-@code{nil} value in order to allow horizontal adjustment of
windows.  Entries are also added that ask for preserving the height of
side windows at the top and bottom of the frame and the width of side
windows at the left or right of the frame.  To assure that side windows
retain their respective sizes when maximizing the frame, the variable
@code{window-resize-pixelwise} is set to a non-@code{nil} value.
@xref{Resizing Windows}.

   The last form also makes sure that none of the created side windows
are accessible via @w{@kbd{C-x o}} by installing the @code{no-other-window}
parameter for each of these windows.  In addition, it makes sure that
side windows are not deleted via @w{@kbd{C-x 1}} by installing the
@code{no-delete-other-windows} parameter for each of these windows.

   Since @code{dired} buffers have no fixed names, we use a special
function @code{dired-default-directory-on-left} in order to display a
lean directory buffer on the left side of the frame.

@example
@group
(defun dired-default-directory-on-left ()
  "Display `default-directory' in side window on left, hiding details."
  (interactive)
  (let ((buffer (dired-noselect default-directory)))
    (with-current-buffer buffer (dired-hide-details-mode t))
    (display-buffer-in-side-window
     buffer `((side . left) (slot . 0)
              (window-width . fit-window-to-buffer)
              (preserve-size . (t . nil)) ,parameters))))
@end group
@end example

Evaluating the preceding forms and typing, in any order, @w{@kbd{M-x
list-buffers}}, @kbd{C-h f}, @kbd{M-x shell}, @w{@kbd{M-x list-tags}},
and @kbd{M-x dired-default-directory-on-left} should now reproduce the
frame layout sketched above.


@node Atomic Windows
@section Atomic Windows
@cindex atomic windows

Atomic windows are rectangular compositions of at least two live
windows.  They have the following distinctive characteristics:

@itemize @bullet
@item
The function @code{split-window} (@pxref{Splitting Windows}), when
applied to a constituent of an atomic window, will try to create the new
window outside of the atomic window.

@item
The function @code{delete-window} (@pxref{Deleting Windows}), when
applied to a constituent of an atomic window, will try to delete the
entire atomic window instead.

@item
The function @code{delete-other-windows} (@pxref{Deleting Windows}),
when applied to a constituent of an atomic window, will try to make the
atomic window fill its frame or main window (@pxref{Side Windows}).
@end itemize

This means that the basic groups of functions that alter the window
structure treat an atomic window like a live one, thus preserving the
internal structure of the atomic window.

   Atomic windows are useful to construct and preserve window layouts
that are meaningful only when all involved buffers are shown
simultaneously in a specific manner, such as when showing differences
between file revisions, or the same text in different languages or
markups.  They can also be used to permanently display information
pertinent to a specific window in bars on that window's sides.

@cindex root window of atomic window
   Atomic windows are implemented with the help of the reserved
@code{window-atom} window parameter (@pxref{Window Parameters}) and an
internal window (@pxref{Basic Windows}) called the root window of the
atomic window.  All windows that are part of the same atomic window have
this root window as their common ancestor and are assigned a
non-@code{nil} @code{window-atom} parameter.

  The following function returns the root of the atomic window a
specified window is part of:

@defun window-atom-root &optional window
This functions returns the root of the atomic window @var{window} is a
part of.  The specified @var{window} must be a valid window and defaults
to the selected one.  It returns @code{nil} if @var{window} is not part
of an atomic window.
@end defun

The most simple approach to make a new atomic window is to take an
existing internal window and apply the following function:

@defun window-make-atom window
This function converts @var{window} into an atomic window.  The
specified @var{window} must be an internal window.  All this function
does is to set the @code{window-atom} parameter of each descendant of
@var{window} to @code{t}.
@end defun

To create a new atomic window from an existing live window or to add a
new window to an existing atomic window, the following buffer display
action function (@pxref{Buffer Display Action Functions}) can be used:

@defun display-buffer-in-atom-window buffer alist
This function tries to display @var{buffer} in a new window that will be
combined with an existing window to form an atomic window.  If the
existing window is already part of an atomic window, it adds the new
window to that atomic window.

The specified @var{alist} is an association list of symbols and values.
The following symbols have a special meaning:

@table @code
@item window
The value of such an element specifies an existing window the new window
shall be combined with.  If it specifies an internal window, all
children of that window become part of the atomic window too.  If no
window is specified, the new window becomes a sibling of the selected
window.  The @code{window-atom} parameter of the existing window is set
to @code{main} provided that window is live and its @code{window-atom}
parameter was not already set.

@item side
The value of such an element denotes the side of the existing window
where the new window shall be located.  Valid values are @code{below},
@code{right}, @code{above} and @code{left}.  The default is
@code{below}.  The @code{window-atom} parameter of the new window is set
to this value.
@end table

The return value is the new window, @code{nil} when creating that window
failed.
@end defun

Note that the value of the @code{window-atom} parameter does not really
matter as long as it is non-@code{nil}.  The values assigned by
@code{display-buffer-in-atom-window} just allow for easy retrieval of
the original and the new window after that function has been applied.
Note also that the @code{window-atom} parameter is the only window
parameter assigned by @code{display-buffer-in-atom-window}.  Further
parameters have to be set by the application explicitly via a
@code{window-parameters} entry in @var{alist}.

   Atomic windows automatically cease to exist when one of their
constituents gets deleted.  To dissolve an atomic window manually,
reset the @code{window-atom} parameter of its constituents---the root
of the atomic window and all its descendants.

   The following code snippet, when applied to a single-window frame,
first splits the selected window and makes the selected and the new
window constituents of an atomic window with their parent as root.  It
then displays the buffer @file{*Messages*} in a new window at the
frame's bottom and makes that new window part of the atomic window just
created.

@example
@group
(let ((window (split-window-right)))
  (window-make-atom (window-parent window))
  (display-buffer-in-atom-window
   (get-buffer-create "*Messages*")
   `((window . ,(window-parent window)) (window-height . 5))))
@end group
@end example

At this moment typing @w{@kbd{C-x 2}} in any window of that frame
produces a new window at the bottom of the frame.  Typing @w{@kbd{C-x
3}} instead will put the new window at the frame's right.  In either
case, typing now @w{@kbd{C-x 1}} in any window of the atomic window will
remove the new window only.  Typing @w{@kbd{C-x 0}} in any window of the
atomic window will make that new window fill the frame.


@node Window Point
@section Windows and Point
@cindex window position
@cindex window point
@cindex position in window
@cindex point in window

  Each window has its own value of point (@pxref{Point}), independent of
the value of point in other windows displaying the same buffer.  This
makes it useful to have multiple windows showing one buffer.

@itemize @bullet
@item
The window point is established when a window is first created; it is
initialized from the buffer's point, or from the window point of another
window opened on the buffer if such a window exists.

@item
Selecting a window sets the value of point in its buffer from the
window's value of point.  Conversely, deselecting a window sets the
window's value of point from that of the buffer.  Thus, when you switch
between windows that display a given buffer, the point value for the
selected window is in effect in the buffer, while the point values for
the other windows are stored in those windows.

@item
As long as the selected window displays the current buffer, the window's
point and the buffer's point always move together; they remain equal.
@end itemize

@cindex cursor
   Emacs displays the cursor, by default as a rectangular block, in
each window at the position of that window's point.  When the user
switches to another buffer in a window, Emacs moves that window's
cursor to where point is in that buffer.  If the exact position of
point is hidden behind some display element, such as a display string
or an image, Emacs displays the cursor immediately before or after
that display element.

@defun window-point &optional window
This function returns the current position of point in @var{window}.
For a nonselected window, this is the value point would have (in that
window's buffer) if that window were selected.  The default for
@var{window} is the selected window.

When @var{window} is the selected window, the value returned is the
value of point in that window's buffer.  Strictly speaking, it would be
more correct to return the top-level value of point, outside of any
@code{save-excursion} forms.  But that value is hard to find.
@end defun

@defun set-window-point window position
This function positions point in @var{window} at position
@var{position} in @var{window}'s buffer.  It returns @var{position}.

If @var{window} is selected, this simply does @code{goto-char} in
@var{window}'s buffer.
@end defun

@defvar window-point-insertion-type
This variable specifies the marker insertion type (@pxref{Marker
Insertion Types}) of @code{window-point}.  The default is @code{nil},
so @code{window-point} will stay behind text inserted there.
@end defvar

@node Window Start and End
@section The Window Start and End Positions
@cindex window start position
@cindex display-start position

  Each window maintains a marker used to keep track of a buffer position
that specifies where in the buffer display should start.  This position
is called the @dfn{display-start} position of the window (or just the
@dfn{start}).  The character after this position is the one that appears
at the upper left corner of the window.  It is usually, but not
inevitably, at the beginning of a text line.

  After switching windows or buffers, and in some other cases, if the
window start is in the middle of a line, Emacs adjusts the window
start to the start of a line.  This prevents certain operations from
leaving the window start at a meaningless point within a line.  This
feature may interfere with testing some Lisp code by executing it
using the commands of Lisp mode, because they trigger this
readjustment.  To test such code, put it into a command and bind the
command to a key.

@defun window-start &optional window
@cindex window top line
This function returns the display-start position of window
@var{window}.  If @var{window} is @code{nil}, the selected window is
used.

When you create a window, or display a different buffer in it, the
display-start position is set to a display-start position recently used
for the same buffer, or to @code{point-min} if the buffer doesn't have
any.

Redisplay updates the window-start position (if you have not specified
it explicitly since the previous redisplay)---to make sure point appears
on the screen.  Nothing except redisplay automatically changes the
window-start position; if you move point, do not expect the window-start
position to change in response until after the next redisplay.
@end defun

@defun window-group-start &optional window
@vindex window-group-start-function
This function is like @code{window-start}, except that when
@var{window} is a part of a group of windows (@pxref{Window Group}),
@code{window-group-start} returns the start position of the entire
group.  This condition holds when the buffer local variable
@code{window-group-start-function} is set to a function.  In this
case, @code{window-group-start} calls the function with the single
argument @var{window}, then returns its result.
@end defun

@cindex window end position
@cindex last visible position in a window
@defun window-end &optional window update
This function returns the position where display of its buffer ends in
@var{window}.  The default for @var{window} is the selected window.

Simply changing the buffer text or moving point does not update the
value that @code{window-end} returns.  The value is updated only when
Emacs redisplays and redisplay completes without being preempted.

If the last redisplay of @var{window} was preempted, and did not finish,
Emacs does not know the position of the end of display in that window.
In that case, this function returns @code{nil}.

If @var{update} is non-@code{nil}, @code{window-end} always returns an
up-to-date value for where display ends, based on the current
@code{window-start} value.  If a previously saved value of that position
is still valid, @code{window-end} returns that value; otherwise it
computes the correct value by scanning the buffer text.

Even if @var{update} is non-@code{nil}, @code{window-end} does not
attempt to scroll the display if point has moved off the screen, the
way real redisplay would do.  It does not alter the
@code{window-start} value.  In effect, it reports where the displayed
text will end if scrolling is not required.  Note that the position it
returns might be only partially visible.
@end defun

@vindex window-group-end-function
@defun window-group-end &optional window update
This function is like @code{window-end}, except that when @var{window}
is a part of a group of windows (@pxref{Window Group}),
@code{window-group-end} returns the end position of the entire group.
This condition holds when the buffer local variable
@code{window-group-end-function} is set to a function.  In this case,
@code{window-group-end} calls the function with the two arguments
@var{window} and @var{update}, then returns its result.  The argument
@var{update} has the same meaning as in @code{window-end}.
@end defun

@defun set-window-start window position &optional noforce
This function sets the display-start position of @var{window} to
@var{position} in @var{window}'s buffer.  It returns @var{position}.

The display routines insist that the position of point be visible when a
buffer is displayed.  Normally, they select the display-start position
according to their internal logic (and scroll the window if necessary)
to make point visible.  However, if you specify the start position
with this function using @code{nil} for @var{noforce}, it means you
want display to start at @var{position} even if that would put the
location of point off the screen.  If this does place point off
screen, the display routines attempt to move point to the left margin
on the middle line in the window.

For example, if point @w{is 1} and you set the start of the window
@w{to 37}, the start of the next line, point will be above the top
of the window.  The display routines will automatically move point if
it is still 1 when redisplay occurs.  Here is an example:

@example
@group
;; @r{Here is what @samp{foo} looks like before executing}
;;   @r{the @code{set-window-start} expression.}
@end group

@group
---------- Buffer: foo ----------
@point{}This is the contents of buffer foo.
2
3
4
5
6
---------- Buffer: foo ----------
@end group

@group
(set-window-start
 (selected-window)
 (save-excursion
   (goto-char 1)
   (forward-line 1)
   (point)))
@result{} 37
@end group

@group
;; @r{Here is what @samp{foo} looks like after executing}
;;   @r{the @code{set-window-start} expression.}
---------- Buffer: foo ----------
2
3
@point{}4
5
6
---------- Buffer: foo ----------
@end group
@end example

If the attempt to make point visible (i.e., in a fully-visible screen
line) fails, the display routines will disregard the requested
window-start position and compute a new one anyway.  Thus, for
reliable results Lisp programs that call this function should always
move point to be inside the window whose display starts at
@var{position}.

If @var{noforce} is non-@code{nil}, and @var{position} would place point
off screen at the next redisplay, then redisplay computes a new window-start
position that works well with point, and thus @var{position} is not used.
@end defun

@vindex set-window-group-start-function
@defun set-window-group-start window position &optional noforce
This function is like @code{set-window-start}, except that when
@var{window} is a part of a group of windows (@pxref{Window Group}),
@code{set-window-group-start} sets the start position of the entire
group.  This condition holds when the buffer local variable
@code{set-window-group-start-function} is set to a function.  In this
case, @code{set-window-group-start} calls the function with the three
arguments @var{window}, @var{position}, and @var{noforce}, then
returns its result.  The arguments @var{position} and @var{noforce} in
this function have the same meaning as in @code{set-window-start}.
@end defun

@defun pos-visible-in-window-p &optional position window partially
This function returns non-@code{nil} if @var{position} is within the
range of text currently visible on the screen in @var{window}.  It
returns @code{nil} if @var{position} is scrolled vertically out of
view.  Locations that are partially obscured are not considered
visible unless @var{partially} is non-@code{nil}.  The argument
@var{position} defaults to the current position of point in
@var{window}; @var{window} defaults to the selected window.  If
@var{position} is @code{t}, that means to check either the first
visible position of the last screen line in @var{window}, or the
end-of-buffer position, whichever comes first.

This function considers only vertical scrolling.  If @var{position} is
out of view only because @var{window} has been scrolled horizontally,
@code{pos-visible-in-window-p} returns non-@code{nil} anyway.
@xref{Horizontal Scrolling}.

If @var{position} is visible, @code{pos-visible-in-window-p} returns
@code{t} if @var{partially} is @code{nil}; if @var{partially} is
non-@code{nil}, and the character following @var{position} is fully
visible, it returns a list of the form @code{(@var{x} @var{y})}, where
@var{x} and @var{y} are the pixel coordinates relative to the top left
corner of the window; otherwise it returns an extended list of the form
@code{(@var{x} @var{y} @var{rtop} @var{rbot} @var{rowh} @var{vpos})},
where @var{rtop} and @var{rbot} specify the number of off-window pixels
at the top and bottom of the row at @var{position}, @var{rowh} specifies
the visible height of that row, and @var{vpos} specifies the vertical
position (zero-based row number) of that row.

Here is an example:

@example
@group
;; @r{If point is off the screen now, recenter it now.}
(or (pos-visible-in-window-p
     (point) (selected-window))
    (recenter 0))
@end group
@end example
@end defun

@vindex pos-visible-in-window-group-p-function
@defun pos-visible-in-window-group-p &optional position window partially
This function is like @code{pos-visible-in-window-p}, except that when
@var{window} is a part of a group of windows (@pxref{Window Group}),
@code{pos-visible-in-window-group-p} tests the visibility of @var{pos}
in the entire group, not just in the single @var{window}.  This
condition holds when the buffer local variable
@code{pos-visible-in-window-group-p-function} is set to a function.
In this case @code{pos-visible-in-window-group-p} calls the function
with the three arguments @var{position}, @var{window}, and
@var{partially}, then returns its result.  The arguments
@var{position} and @var{partially} have the same meaning as in
@code{pos-visible-in-window-p}.
@end defun

@defun window-line-height &optional line window
This function returns the height of text line @var{line} in
@var{window}.  If @var{line} is one of @code{header-line} or
@code{mode-line}, @code{window-line-height} returns information about
the corresponding line of the window.  Otherwise, @var{line} is a text
line number starting from 0.  A negative number counts from the end of
the window.  The default for @var{line} is the current line in
@var{window}; the default for @var{window} is the selected window.

If the display is not up to date, @code{window-line-height} returns
@code{nil}.  In that case, @code{pos-visible-in-window-p} may be used
to obtain related information.

If there is no line corresponding to the specified @var{line},
@code{window-line-height} returns @code{nil}.  Otherwise, it returns
a list @code{(@var{height} @var{vpos} @var{ypos} @var{offbot})},
where @var{height} is the height in pixels of the visible part of the
line, @var{vpos} and @var{ypos} are the vertical position in lines and
pixels of the line relative to the top of the first text line, and
@var{offbot} is the number of off-window pixels at the bottom of the
text line.  If there are off-window pixels at the top of the (first)
text line, @var{ypos} is negative.
@end defun

@node Textual Scrolling
@section Textual Scrolling
@cindex textual scrolling
@cindex scrolling textually

  @dfn{Textual scrolling} means moving the text up or down through a
window.  It works by changing the window's display-start location.  It
may also change the value of @code{window-point} to keep point on the
screen (@pxref{Window Point}).

  The basic textual scrolling functions are @code{scroll-up} (which
scrolls forward) and @code{scroll-down} (which scrolls backward).  In
these function names, ``up'' and ``down'' refer to the direction of
motion of the buffer text relative to the window.  Imagine that the
text is written on a long roll of paper and that the scrolling
commands move the paper up and down.  Thus, if you are looking at the
middle of a buffer and repeatedly call @code{scroll-down}, you will
eventually see the beginning of the buffer.

  Unfortunately, this sometimes causes confusion, because some people
tend to think in terms of the opposite convention: they
imagine the window moving over text that remains in place, so that
``down'' commands take you to the end of the buffer.  This convention
is consistent with fact that such a command is bound to a key named
@key{PageDown} on modern keyboards.
@ignore
We have not switched to this convention as that is likely to break
existing Emacs Lisp code.
@end ignore

  Textual scrolling functions (aside from @code{scroll-other-window})
have unpredictable results if the current buffer is not the one
displayed in the selected window.  @xref{Current Buffer}.

  If the window contains a row taller than the height of the window
(for example in the presence of a large image), the scroll functions
will adjust the window's vertical scroll position to scroll the
partially visible row.  Lisp callers can disable this feature by
binding the variable @code{auto-window-vscroll} to @code{nil}
(@pxref{Vertical Scrolling}).

@deffn Command scroll-up &optional count
This function scrolls forward by @var{count} lines in the selected
window.

If @var{count} is negative, it scrolls backward instead.  If
@var{count} is @code{nil} (or omitted), the distance scrolled is
@code{next-screen-context-lines} lines less than the height of the
window's text area.

If the selected window cannot be scrolled any further, this function
signals an error.  Otherwise, it returns @code{nil}.
@end deffn

@deffn Command scroll-down &optional count
This function scrolls backward by @var{count} lines in the selected
window.

If @var{count} is negative, it scrolls forward instead.  In other
respects, it behaves the same way as @code{scroll-up} does.
@end deffn

@deffn Command scroll-up-command &optional count
This behaves like @code{scroll-up}, except that if the selected window
cannot be scrolled any further and the value of the variable
@code{scroll-error-top-bottom} is @code{t}, it tries to move to the
end of the buffer instead.  If point is already there, it signals an
error.
@end deffn

@deffn Command scroll-down-command &optional count
This behaves like @code{scroll-down}, except that if the selected
window cannot be scrolled any further and the value of the variable
@code{scroll-error-top-bottom} is @code{t}, it tries to move to the
beginning of the buffer instead.  If point is already there, it
signals an error.
@end deffn

@deffn Command scroll-other-window &optional count
This function scrolls the text in another window upward @var{count}
lines.  Negative values of @var{count}, or @code{nil}, are handled
as in @code{scroll-up}.

You can specify which buffer to scroll by setting the variable
@code{other-window-scroll-buffer} to a buffer.  If that buffer isn't
already displayed, @code{scroll-other-window} displays it in some
window.

When the selected window is the minibuffer, the next window is normally
the leftmost one immediately above it.  You can specify a different
window to scroll, when the minibuffer is selected, by setting the variable
@code{minibuffer-scroll-window}.  This variable has no effect when any
other window is selected.  When it is non-@code{nil} and the
minibuffer is selected, it takes precedence over
@code{other-window-scroll-buffer}.  @xref{Definition of
minibuffer-scroll-window}.

When the minibuffer is active, it is the next window if the selected
window is the one at the bottom right corner.  In this case,
@code{scroll-other-window} attempts to scroll the minibuffer.  If the
minibuffer contains just one line, it has nowhere to scroll to, so the
line reappears after the echo area momentarily displays the message
@samp{End of buffer}.
@end deffn

@deffn Command scroll-other-window-down &optional count
This function scrolls the text in another window downward @var{count}
lines.  Negative values of @var{count}, or @code{nil}, are handled as
in @code{scroll-down}.  In other respects, it behaves the same way as
@code{scroll-other-window} does.
@end deffn

@defvar other-window-scroll-buffer
If this variable is non-@code{nil}, it tells @code{scroll-other-window}
which buffer's window to scroll.
@end defvar

@defopt scroll-margin
This option specifies the size of the scroll margin---a minimum number
of lines between point and the top or bottom of a window.  Whenever
point gets within this many lines of the top or bottom of the window,
redisplay scrolls the text automatically (if possible) to move point
out of the margin, closer to the center of the window.
@end defopt

@defopt maximum-scroll-margin
This variable limits the effective value of @code{scroll-margin} to a
fraction of the current window line height.  For example, if the
current window has 20 lines and @code{maximum-scroll-margin} is 0.1,
then the scroll margins will never be larger than 2 lines, no matter
how big @code{scroll-margin} is.

@code{maximum-scroll-margin} itself has a maximum value of 0.5, which
allows setting margins large to keep the cursor at the middle line of
the window (or two middle lines if the window has an even number of
lines).  If it's set to a larger value (or any value other than a
float between 0.0 and 0.5) then the default value of 0.25 will be used
instead.
@end defopt

@defopt scroll-conservatively
This variable controls how scrolling is done automatically when point
moves off the screen (or into the scroll margin).  If the value is a
positive integer @var{n}, then redisplay scrolls the text up to
@var{n} lines in either direction, if that will bring point back into
proper view.  This behavior is called @dfn{conservative scrolling}.
Otherwise, scrolling happens in the usual way, under the control of
other variables such as @code{scroll-up-aggressively} and
@code{scroll-down-aggressively}.

The default value is zero, which means that conservative scrolling
never happens.
@end defopt

@defopt scroll-down-aggressively
The value of this variable should be either @code{nil} or a fraction
@var{f} between 0 and 1.  If it is a fraction, that specifies where on
the screen to put point when scrolling down.  More precisely, when a
window scrolls down because point is above the window start, the new
start position is chosen to put point @var{f} part of the window
height from the top.  The larger @var{f}, the more aggressive the
scrolling.

A value of @code{nil} is equivalent to .5, since its effect is to center
point.  This variable automatically becomes buffer-local when set in any
fashion.
@end defopt

@defopt scroll-up-aggressively
Likewise, for scrolling up.  The value, @var{f}, specifies how far
point should be placed from the bottom of the window; thus, as with
@code{scroll-down-aggressively}, a larger value scrolls more
aggressively.
@end defopt

@defopt scroll-step
This variable is an older variant of @code{scroll-conservatively}.
The difference is that if its value is @var{n}, that permits scrolling
only by precisely @var{n} lines, not a smaller number.  This feature
does not work with @code{scroll-margin}.  The default value is zero.
@end defopt

@cindex @code{scroll-command} property
@defopt scroll-preserve-screen-position
If this option is @code{t}, whenever a scrolling command moves point
off-window, Emacs tries to adjust point to keep the cursor at its old
vertical position in the window, rather than the window edge.

If the value is non-@code{nil} and not @code{t}, Emacs adjusts point
to keep the cursor at the same vertical position, even if the
scrolling command didn't move point off-window.

This option affects all scroll commands that have a non-@code{nil}
@code{scroll-command} symbol property.
@end defopt

@defopt next-screen-context-lines
The value of this variable is the number of lines of continuity to
retain when scrolling by full screens.  For example, @code{scroll-up}
with an argument of @code{nil} scrolls so that this many lines at the
bottom of the window appear instead at the top.  The default value is
@code{2}.
@end defopt

@defopt scroll-error-top-bottom
If this option is @code{nil} (the default), @code{scroll-up-command}
and @code{scroll-down-command} simply signal an error when no more
scrolling is possible.

If the value is @code{t}, these commands instead move point to the
beginning or end of the buffer (depending on scrolling direction);
only if point is already on that position do they signal an error.
@end defopt

@deffn Command recenter &optional count redisplay
@cindex centering point
This function scrolls the text in the selected window so that point is
displayed at a specified vertical position within the window.  It does
not move point with respect to the text.

If @var{count} is a non-negative number, that puts the line containing
point @var{count} lines down from the top of the window.  If
@var{count} is a negative number, then it counts upward from the
bottom of the window, so that @minus{}1 stands for the last usable
line in the window.

If @var{count} is @code{nil} (or a non-@code{nil} list),
@code{recenter} puts the line containing point in the middle of the
window.  If @var{count} is @code{nil} and @var{redisplay} is
non-@code{nil}, this function may redraw the frame, according to the
value of @code{recenter-redisplay}.  Thus, omitting the second
argument can be used to countermand the effect of
@code{recenter-redisplay} being non-@code{nil}.  Interactive calls
pass non-‘nil’ for @var{redisplay}.

When @code{recenter} is called interactively, @var{count} is the raw
prefix argument.  Thus, typing @kbd{C-u} as the prefix sets the
@var{count} to a non-@code{nil} list, while typing @kbd{C-u 4} sets
@var{count} to 4, which positions the current line four lines from the
top.

With an argument of zero, @code{recenter} positions the current line at
the top of the window.  The command @code{recenter-top-bottom} offers
a more convenient way to achieve this.
@end deffn

@vindex recenter-window-group-function
@defun recenter-window-group &optional count
This function is like @code{recenter}, except that when the selected
window is part of a group of windows (@pxref{Window Group}),
@code{recenter-window-group} scrolls the entire group.  This condition
holds when the buffer local variable
@code{recenter-window-group-function} is set to a function.  In this
case, @code{recenter-window-group} calls the function with the
argument @var{count}, then returns its result.  The argument
@var{count} has the same meaning as in @code{recenter}, but with
respect to the entire window group.
@end defun

@defopt recenter-redisplay
If this variable is non-@code{nil}, calling @code{recenter} with a
@code{nil} @var{count} argument and non-@code{nil} @var{redisplay}
argument redraws the frame.  The default value is @code{tty}, which
means only redraw the frame if it is a tty frame.
@end defopt

@deffn Command recenter-top-bottom &optional count
This command, which is the default binding for @kbd{C-l}, acts like
@code{recenter}, except if called with no argument.  In that case,
successive calls place point according to the cycling order defined
by the variable @code{recenter-positions}.
@end deffn

@defopt recenter-positions
This variable controls how @code{recenter-top-bottom} behaves when
called with no argument.  The default value is @code{(middle top
bottom)}, which means that successive calls of
@code{recenter-top-bottom} with no argument cycle between placing
point at the middle, top, and bottom of the window.
@end defopt


@node Vertical Scrolling
@section Vertical Fractional Scrolling
@cindex vertical fractional scrolling
@cindex vertical scroll position

   @dfn{Vertical fractional scrolling} means shifting text in a window
up or down by a specified multiple or fraction of a line.  Emacs uses
it, for example, on images and screen lines which are taller than the
window.  Each window has a @dfn{vertical scroll position}, which is a
number, never less than zero.  It specifies how far to raise the
contents of the window when displaying them.  Raising the window
contents generally makes all or part of some lines disappear off the
top, and all or part of some other lines appear at the bottom.  The
usual value is zero.

   The vertical scroll position is measured in units of the normal line
height, which is the height of the default font.  Thus, if the value is
.5, that means the window contents will be scrolled up half the normal
line height.  If it is 3.3, that means the window contents are scrolled
up somewhat over three times the normal line height.

   What fraction of a line the vertical scrolling covers, or how many
lines, depends on what the lines contain.  A value of .5 could scroll a
line whose height is very short off the screen, while a value of 3.3
could scroll just part of the way through a tall line or an image.

@defun window-vscroll &optional window pixels-p
This function returns the current vertical scroll position of
@var{window}.  The default for @var{window} is the selected window.
If @var{pixels-p} is non-@code{nil}, the return value is measured in
pixels, rather than in units of the normal line height.

@example
@group
(window-vscroll)
     @result{} 0
@end group
@end example
@end defun

@defun set-window-vscroll window lines &optional pixels-p
This function sets @var{window}'s vertical scroll position to
@var{lines}.  If @var{window} is @code{nil}, the selected window is
used.  The argument @var{lines} should be zero or positive; if not, it
is taken as zero.


The actual vertical scroll position must always correspond
to an integral number of pixels, so the value you specify
is rounded accordingly.

The return value is the result of this rounding.

@example
@group
(set-window-vscroll (selected-window) 1.2)
     @result{} 1.13
@end group
@end example

If @var{pixels-p} is non-@code{nil}, @var{lines} specifies a number of
pixels.  In this case, the return value is @var{lines}.
@end defun

@defvar auto-window-vscroll
If this variable is non-@code{nil}, the @code{line-move},
@code{scroll-up}, and @code{scroll-down} functions will automatically
modify the vertical scroll position to scroll through display rows
that are taller than the height of the window, for example in the
presence of large images.
@end defvar

@node Horizontal Scrolling
@section Horizontal Scrolling
@cindex horizontal scrolling

  @dfn{Horizontal scrolling} means shifting the image in the window left
or right by a specified multiple of the normal character width.  Each
window has a @dfn{horizontal scroll position}, which is a number, never
less than zero.  It specifies how far to shift the contents left.
Shifting the window contents left generally makes all or part of some
characters disappear off the left, and all or part of some other
characters appear at the right.  The usual value is zero.

  The horizontal scroll position is measured in units of the normal
character width, which is the width of space in the default font.  Thus,
if the value is 5, that means the window contents are scrolled left by 5
times the normal character width.  How many characters actually
disappear off to the left depends on their width, and could vary from
line to line.

  Because we read from side to side in the inner loop, and from top
to bottom in the outer loop, the effect of horizontal scrolling is
not like that of textual or vertical scrolling.  Textual scrolling
involves selection of a portion of text to display, and vertical
scrolling moves the window contents contiguously; but horizontal
scrolling causes part of @emph{each line} to go off screen.

  Usually, no horizontal scrolling is in effect; then the leftmost
column is at the left edge of the window.  In this state, scrolling to
the right is meaningless, since there is no data to the left of the edge
to be revealed by it; so this is not allowed.  Scrolling to the left is
allowed; it scrolls the first columns of text off the edge of the window
and can reveal additional columns on the right that were truncated
before.  Once a window has a nonzero amount of leftward horizontal
scrolling, you can scroll it back to the right, but only so far as to
reduce the net horizontal scroll to zero.  There is no limit to how far
left you can scroll, but eventually all the text will disappear off the
left edge.

@vindex auto-hscroll-mode
  If @code{auto-hscroll-mode} is set, redisplay automatically alters
the horizontal scrolling of a window as necessary to ensure that point
is always visible.  However, you can still set the horizontal
scrolling value explicitly.  The value you specify serves as a lower
bound for automatic scrolling, i.e., automatic scrolling will not
scroll a window to a column less than the specified one.

  The default value of @code{auto-hscroll-mode} is @code{t}; setting
it to @code{current-line} activates a variant of automatic horizontal
scrolling whereby only the line showing the cursor is horizontally
scrolled to make point visible, the rest of the window is left either
unscrolled, or at the minimum scroll amount set by @code{scroll-left}
and @code{scroll-right}, see below.

@deffn Command scroll-left &optional count set-minimum
This function scrolls the selected window @var{count} columns to the
left (or to the right if @var{count} is negative).  The default
for @var{count} is the window width, minus 2.

The return value is the total amount of leftward horizontal scrolling in
effect after the change---just like the value returned by
@code{window-hscroll} (below).

Note that text in paragraphs whose base direction is right-to-left
(@pxref{Bidirectional Display}) moves in the opposite direction: e.g.,
it moves to the right when @code{scroll-left} is invoked with a
positive value of @var{count}.

Once you scroll a window as far right as it can go, back to its normal
position where the total leftward scrolling is zero, attempts to scroll
any farther right have no effect.

If @var{set-minimum} is non-@code{nil}, the new scroll amount becomes
the lower bound for automatic scrolling; that is, automatic scrolling
will not scroll a window to a column less than the value returned by
this function.  Interactive calls pass non-@code{nil} for
@var{set-minimum}.
@end deffn

@deffn Command scroll-right &optional count set-minimum
This function scrolls the selected window @var{count} columns to the
right (or to the left if @var{count} is negative).  The default
for @var{count} is the window width, minus 2.  Aside from the direction
of scrolling, this works just like @code{scroll-left}.
@end deffn

@defun window-hscroll &optional window
This function returns the total leftward horizontal scrolling of
@var{window}---the number of columns by which the text in @var{window}
is scrolled left past the left margin.  (In right-to-left paragraphs,
the value is the total amount of the rightward scrolling instead.)
The default for @var{window} is the selected window.

The return value is never negative.  It is zero when no horizontal
scrolling has been done in @var{window} (which is usually the case).


@example
@group
(window-hscroll)
     @result{} 0
@end group
@group
(scroll-left 5)
     @result{} 5
@end group
@group
(window-hscroll)
     @result{} 5
@end group
@end example
@end defun

@defun set-window-hscroll window columns
This function sets horizontal scrolling of @var{window}.  The value of
@var{columns} specifies the amount of scrolling, in terms of columns
from the left margin (right margin in right-to-left paragraphs).  The
argument @var{columns} should be zero or positive; if not, it is taken
as zero.  Fractional values of @var{columns} are not supported at
present.

Note that @code{set-window-hscroll} may appear not to work if you test
it by evaluating a call with @kbd{M-:} in a simple way.  What happens
is that the function sets the horizontal scroll value and returns, but
then redisplay adjusts the horizontal scrolling to make point visible,
and this overrides what the function did.  You can observe the
function's effect if you call it while point is sufficiently far from
the left margin that it will remain visible.

The value returned is @var{columns}.

@example
@group
(set-window-hscroll (selected-window) 10)
     @result{} 10
@end group
@end example
@end defun

   Here is how you can determine whether a given position @var{position}
is off the screen due to horizontal scrolling:

@c FIXME: Maybe hscroll-on-screen-p is a better name?
@example
@group
(defun hscroll-on-screen (window position)
  (save-excursion
    (goto-char position)
    (and
     (>= (- (current-column) (window-hscroll window)) 0)
     (< (- (current-column) (window-hscroll window))
        (window-width window)))))
@end group
@end example


@node Coordinates and Windows
@section Coordinates and Windows
@cindex frame-relative coordinate
@cindex coordinate, relative to frame
@cindex window position

This section describes functions that report positions of and within a
window.  Most of these functions report positions relative to an origin
at the native position of the window's frame (@pxref{Frame Geometry}).
Some functions report positions relative to the origin of the display of
the window's frame.  In any case, the origin has the coordinates (0, 0)
and X and Y coordinates increase rightward and downward respectively.

  For the following functions, X and Y coordinates are reported in
integer character units, i.e., numbers of lines and columns
respectively.  On a graphical display, each ``line'' and ``column''
corresponds to the height and width of the default character specified by
the frame's default font (@pxref{Frame Font}).

@defun window-edges &optional window body absolute pixelwise
This function returns a list of the edge coordinates of @var{window}.
If @var{window} is omitted or @code{nil}, it defaults to the selected
window.

The return value has the form @code{(@var{left} @var{top} @var{right}
@var{bottom})}.  These list elements are, respectively, the X
coordinate of the leftmost column occupied by the window, the Y
coordinate of the topmost row, the X coordinate one column to the
right of the rightmost column, and the Y coordinate one row down from
the bottommost row.

Note that these are the actual outer edges of the window, including any
header line, mode line, scroll bar, fringes, window divider and display
margins.  On a text terminal, if the window has a neighbor on its right,
its right edge includes the separator line between the window and its
neighbor.

If the optional argument @var{body} is @code{nil}, this means to
return the edges corresponding to the total size of @var{window}.
@var{body} non-@code{nil} means to return the edges of @var{window}'s
body (aka text area).  If @var{body} is non-@code{nil}, @var{window}
must specify a live window.

If the optional argument @var{absolute} is @code{nil}, this means to
return edges relative to the native position of @var{window}'s frame.
@var{absolute} non-@code{nil} means to return coordinates relative to
the origin (0, 0) of @var{window}'s display.  On non-graphical systems
this argument has no effect.

If the optional argument @var{pixelwise} is @code{nil}, this means to
return the coordinates in terms of the default character width and
height of @var{window}'s frame (@pxref{Frame Font}), rounded if
necessary.  @var{pixelwise} non-@code{nil} means to return the
coordinates in pixels.  Note that the pixel specified by @var{right} and
@var{bottom} is immediately outside of these edges.  If @var{absolute}
is non-@code{nil}, @var{pixelwise} is implicitly non-@code{nil} too.
@end defun

@defun window-body-edges &optional window
This function returns the edges of @var{window}'s body (@pxref{Window
Sizes}).  Calling @code{(window-body-edges window)} is equivalent to
calling @code{(window-edges window t)}, see above.
@end defun

@comment The following two functions are confusing and hardly used.
@ignore
@defun window-left-column &optional window
This function returns the leftmost column of @var{window}.  This value
equals the @var{left} entry in the list returned by @code{(window-edges
window)} minus the number of columns occupied by the internal border of
@var{window}'s frame.
@end defun

@defun window-top-line &optional window
This function returns the topmost row of @var{window}.  This value is
equal to the @var{top} entry in the list returned by @code{(window-edges
window)} minus the number of lines occupied by the internal border of
@var{window}'s frame.
@end defun
@end ignore

  The following functions can be used to relate a set of
frame-relative coordinates to a window:

@defun window-at x y &optional frame
This function returns the live window at the coordinates @var{x} and
@var{y} given in default character sizes (@pxref{Frame Font}) relative
to the native position of @var{frame} (@pxref{Frame Geometry}).

If there is no window at that position, the return value is @code{nil}.
If @var{frame} is omitted or @code{nil}, it defaults to the selected
frame.
@end defun

@defun coordinates-in-window-p coordinates window
This function checks whether a window @var{window} occupies the frame
relative coordinates @var{coordinates}, and if so, which part of the
window that is.  @var{window} should be a live window.

@var{coordinates} should be a cons cell of the form @code{(@var{x}
. @var{y})}, where @var{x} and @var{y} are given in default character
sizes (@pxref{Frame Font}) relative to the native position of
@var{window}'s frame (@pxref{Frame Geometry}).

If there is no window at the specified position, the return value is
@code{nil} .  Otherwise, the return value is one of the following:

@table @code
@item (@var{relx} . @var{rely})
The coordinates are inside @var{window}.  The numbers @var{relx} and
@var{rely} are the equivalent window-relative coordinates for the
specified position, counting from 0 at the top left corner of the
window.

@item mode-line
The coordinates are in the mode line of @var{window}.

@item header-line
The coordinates are in the header line of @var{window}.

@item tab-line
The coordinates are in the tab line of @var{window}.

@item right-divider
The coordinates are in the divider separating @var{window} from a
window on the right.

@item bottom-divider
The coordinates are in the divider separating @var{window} from a
window beneath.

@item vertical-line
The coordinates are in the vertical line between @var{window} and its
neighbor to the right.  This value occurs only if the window doesn't
have a scroll bar; positions in a scroll bar are considered outside the
window for these purposes.

@item left-fringe
@itemx right-fringe
The coordinates are in the left or right fringe of the window.

@item left-margin
@itemx right-margin
The coordinates are in the left or right margin of the window.

@item nil
The coordinates are not in any part of @var{window}.
@end table

The function @code{coordinates-in-window-p} does not require a frame as
argument because it always uses the frame that @var{window} is on.
@end defun

  The following functions return window positions in pixels, rather
than character units.  Though mostly useful on graphical displays,
they can also be called on text terminals, where the screen area of
each text character is taken to be one pixel.

@defun window-pixel-edges &optional window
This function returns a list of pixel coordinates for the edges of
@var{window}.  Calling @code{(window-pixel-edges window)} is equivalent
to calling @code{(window-edges window nil nil t)}, see above.
@end defun

@comment The following two functions are confusing and hardly used.
@ignore
@defun window-pixel-left &optional window
This function returns the left pixel edge of window @var{window}.  This
value equals the @var{left} entry in the list returned by
@code{(window-pixel-edges window)} minus the number of pixels occupied
by the internal border of @var{window}'s frame.  @var{window} must be a
valid window and defaults to the selected one.
@end defun

@defun window-pixel-top &optional window
This function returns the top pixel edge of window @var{window}.  This
value is equal to the @var{top} entry in the list returned by
@code{(window-pixel-edges window)} minus the number of pixels occupied
by the internal border of @var{window}'s frame.  @var{window} must be a
valid window and defaults to the selected one.
@end defun
@end ignore

@defun window-body-pixel-edges &optional window
This function returns the pixel edges of @var{window}'s body.  Calling
@code{(window-body-pixel-edges window)} is equivalent to calling
@code{(window-edges window t nil t)}, see above.
@end defun

  The following functions return window positions in pixels, relative to
the origin of the display screen rather than that of the frame:

@defun window-absolute-pixel-edges &optional window
This function returns the pixel coordinates of @var{window} relative to
an origin at (0, 0) of the display of @var{window}'s frame.  Calling
@code{(window-absolute-pixel-edges)} is equivalent to calling
@code{(window-edges window nil t t)}, see above.
@end defun

@defun window-absolute-body-pixel-edges &optional window
This function returns the pixel coordinates of @var{window}'s body
relative to an origin at (0, 0) of the display of @var{window}'s frame.
Calling @code{(window-absolute-body-pixel-edges window)} is equivalent
to calling @code{(window-edges window t t t)}, see above.

Combined with @code{set-mouse-absolute-pixel-position}, this function
can be used to move the mouse pointer to an arbitrary buffer position
visible in some window:

@example
@group
(let ((edges (window-absolute-body-pixel-edges))
      (position (pos-visible-in-window-p nil nil t)))
  (set-mouse-absolute-pixel-position
   (+ (nth 0 edges) (nth 0 position))
   (+ (nth 1 edges) (nth 1 position))))
@end group
@end example

On a graphical terminal this form ``warps'' the mouse cursor to the
upper left corner of the glyph at the selected window's point.  A
position calculated this way can be also used to show a tooltip window
there.
@end defun

The following function returns the screen coordinates of a buffer
position visible in a window:

@defun window-absolute-pixel-position &optional position window
If the buffer position @var{position} is visible in window @var{window},
this function returns the display coordinates of the upper/left corner
of the glyph at @var{position}.  The return value is a cons of the X-
and Y-coordinates of that corner, relative to an origin at (0, 0) of
@var{window}'s display.  It returns @code{nil} if @var{position} is not
visible in @var{window}.

@var{window} must be a live window and defaults to the selected
window.  @var{position} defaults to the value of @code{window-point}
of @var{window}.

This means that in order to move the mouse pointer to the position of
point in the selected window, it's sufficient to write:

@example
@group
(let ((position (window-absolute-pixel-position)))
  (set-mouse-absolute-pixel-position
   (car position) (cdr position)))
@end group
@end example
@end defun

The following function returns the largest rectangle that can be
inscribed in a window without covering text displayed in that window.

@defun window-largest-empty-rectangle &optional window count min-width min-height positions left
This function calculates the dimensions of the largest empty rectangle
that can be inscribed in the specified @var{window}'s text area.
@var{window} must be a live window and defaults to the selected one.

The return value is a triple of the width and the start and end
y-coordinates of the largest rectangle that can be inscribed into the
empty space (space not displaying any text) of the text area of
@var{window}.  No x-coordinates are returned by this function---any such
rectangle is assumed to end at the right edge of @var{window}'s text
area.  If no empty space can be found, the return value is @code{nil}.

The optional argument @var{count}, if non-@code{nil}, specifies a
maximum number of rectangles to return.  This means that the return
value is a list of triples specifying rectangles with the largest
rectangle first.  @var{count} can be also a cons cell whose car
specifies the number of rectangles to return and whose @sc{cdr}, if
non-@code{nil}, states that all rectangles returned must be disjoint.

The optional arguments @var{min-width} and @var{min-height}, if
non-@code{nil}, specify the minimum width and height of any rectangle
returned.

The optional argument @var{positions}, if non-@code{nil}, is a cons cell
whose @sc{car} specifies the uppermost and whose @sc{cdr} specifies the
lowermost pixel position that must be covered by any rectangle returned.
These positions measure from the start of the text area of @var{window}.

The optional argument @var{left}, if non-@code{nil}, means to return
values suitable for buffers displaying right to left text.  In that
case, any rectangle returned is assumed to start at the left edge of
@var{window}'s text area.

Note that this function has to retrieve the dimensions of each line of
@var{window}'s glyph matrix via @code{window-lines-pixel-dimensions}
(@pxref{Size of Displayed Text}).  Hence, this function may also return
@code{nil} when the current glyph matrix of @var{window} is not
up-to-date.
@end defun


@node Mouse Window Auto-selection
@section Mouse Window Auto-selection
@cindex window auto-selection
@cindex auto-selection of window
The following option allows to automatically select the window under the
mouse pointer.  This accomplishes a policy similar to that of window
managers that give focus to a frame (and thus trigger its subsequent
selection) whenever the mouse pointer enters its window-system window
(@pxref{Input Focus}).

@defopt mouse-autoselect-window
If this variable is non-@code{nil}, Emacs will try to automatically
select the window under the mouse pointer.  The following values are
meaningful:

@table @asis
@item A positive number
This specifies a delay in seconds after which auto-selection triggers.
The window under the mouse pointer is selected after the mouse has
remained in it for the entire duration of the delay.

@item A negative number
A negative number has a similar effect as a positive number, but selects
the window under the mouse pointer only after the mouse pointer has
remained in it for the entire duration of the absolute value of that
number and in addition has stopped moving.

@item Other value
Any other non-@code{nil} value means to select a window instantaneously
as soon as the mouse pointer enters it.
@end table

In either case, the mouse pointer must enter the text area of a window in
order to trigger its selection.  Dragging the scroll bar slider or the
mode line of a window conceptually should not cause its auto-selection.

Mouse auto-selection selects the minibuffer window only if it is active,
and never deselects the active minibuffer window.
@end defopt

Mouse auto-selection can be used to emulate a focus follows mouse policy
for child frames (@pxref{Child Frames}) which usually are not tracked by
the window manager.  This requires to set the value of
@code{focus-follows-mouse} (@pxref{Input Focus}) to a non-@code{nil}
value.  If the value of @code{focus-follows-mouse} is @code{auto-raise},
entering a child frame with the mouse will raise it automatically above
all other child frames of that frame's parent frame.


@node Window Configurations
@section Window Configurations
@cindex window configurations
@cindex saving window information

A @dfn{window configuration} records the entire layout of one
frame---all windows, their sizes, which buffers they contain, how those
buffers are scrolled, and their value of point; also their
fringes, margins, and scroll bar settings.  It also includes the value
of @code{minibuffer-scroll-window}.  As a special exception, the window
configuration does not record the value of point in the selected window
for the current buffer.

  You can bring back an entire frame layout by restoring a previously
saved window configuration.  If you want to record the layout of all
frames instead of just one, use a frame configuration instead of a
window configuration.  @xref{Frame Configurations}.

@defun current-window-configuration &optional frame
This function returns a new object representing @var{frame}'s current
window configuration.  The default for @var{frame} is the selected
frame.  The variable @code{window-persistent-parameters} specifies
which window parameters (if any) are saved by this function.
@xref{Window Parameters}.
@end defun

@defun set-window-configuration configuration
This function restores the configuration of windows and buffers as
specified by @var{configuration}, for the frame that @var{configuration}
was created for.

The argument @var{configuration} must be a value that was previously
returned by @code{current-window-configuration}.  The configuration is
restored in the frame from which @var{configuration} was made, whether
that frame is selected or not.  In some rare cases this may trigger
execution of the @code{window-size-change-functions} (@pxref{Window
Hooks}) even if the size of windows did not change at all.  The
@code{window-configuration-change-hook} functions will be called if and
only if at least one window was added to or deleted from the frame.

If the frame from which @var{configuration} was saved is dead, all this
function does is restore the three variables @code{window-min-height},
@code{window-min-width} and @code{minibuffer-scroll-window}.  In this
case, the function returns @code{nil}.  Otherwise, it returns @code{t}.

Here is a way of using this function to get the same effect
as @code{save-window-excursion}:

@example
@group
(let ((config (current-window-configuration)))
  (unwind-protect
      (progn (split-window-below nil)
             @dots{})
    (set-window-configuration config)))
@end group
@end example
@end defun

@defmac save-window-excursion forms@dots{}
This macro records the window configuration of the selected frame,
executes @var{forms} in sequence, then restores the earlier window
configuration.  The return value is the value of the final form in
@var{forms}.

Most Lisp code should not use this macro; @code{save-selected-window}
is typically sufficient.  In particular, this macro cannot reliably
prevent the code in @var{forms} from opening new windows, because new
windows might be opened in other frames (@pxref{Choosing Window}), and
@code{save-window-excursion} only saves and restores the window
configuration on the current frame.
@end defmac

@defun window-configuration-p object
This function returns @code{t} if @var{object} is a window configuration.
@end defun

@defun compare-window-configurations config1 config2
This function compares two window configurations as regards the
structure of windows, but ignores the values of point and the
saved scrolling positions---it can return @code{t} even if those
aspects differ.

The function @code{equal} can also compare two window configurations; it
regards configurations as unequal if they differ in any respect, even a
saved point.
@end defun

@defun window-configuration-frame config
This function returns the frame for which the window configuration
@var{config} was made.
@end defun

  Other primitives to look inside of window configurations would make
sense, but are not implemented because we did not need them.  See the
file @file{winner.el} for some more operations on windows
configurations.

  The objects returned by @code{current-window-configuration} die
together with the Emacs process.  In order to store a window
configuration on disk and read it back in another Emacs session, you
can use the functions described next.  These functions are also useful
to clone the state of a frame into an arbitrary live window
(@code{set-window-configuration} effectively clones the windows of a
frame into the root window of that very frame only).

@cindex window state
@defun window-state-get &optional window writable
This function returns the state of @var{window} as a Lisp object.  The
argument @var{window} must be a valid window and defaults to the root
window of the selected frame.

If the optional argument @var{writable} is non-@code{nil}, this means to
not use markers for sampling positions like @code{window-point} or
@code{window-start}.  This argument should be non-@code{nil} when the
state will be written to disk and read back in another session.

Together, the argument @var{writable} and the variable
@code{window-persistent-parameters} specify which window parameters are
saved by this function.  @xref{Window Parameters}.
@end defun

The value returned by @code{window-state-get} can be used in the same
session to make a clone of a window in another window.  It can be also
written to disk and read back in another session.  In either case, use
the following function to restore the state of the window.

@defun window-state-put state &optional window ignore
This function puts the window state @var{state} into @var{window}.
The argument @var{state} should be the state of a window returned by
an earlier invocation of @code{window-state-get}, see above.  The
optional argument @var{window} can be either a live window or an
internal window (@pxref{Windows and Frames}).  If @var{window} is not
a live window, it is replaced by a new live window created on the same
frame before putting @var{state} into it.  If @var{window} is @code{nil},
it puts the window state into a new window.

If the optional argument @var{ignore} is non-@code{nil}, it means to ignore
minimum window sizes and fixed-size restrictions.  If @var{ignore}
is @code{safe}, this means windows can get as small as one line
and/or two columns.
@end defun

The functions @code{window-state-get} and @code{window-state-put} also
allow to exchange the contents of two live windows.  The following
function does precisely that:

@deffn Command window-swap-states &optional window-1 window-2 size
This command swaps the states of the two live windows @var{window-1} and
@var{window-2}.  @var{window-1} must specify a live window and defaults
to the selected one.  @var{window-2} must specify a live window and
defaults to the window following @var{window-1} in the cyclic ordering
of windows, excluding minibuffer windows and including live windows on
all visible frames.

Optional argument @var{size} non-@code{nil} means to try swapping the
sizes of @var{window-1} and @var{window-2} as well.  A value of
@code{height} means to swap heights only, a value of @code{width}
means to swap widths only, while @code{t} means to swap both widths
and heights, if possible.  Frames are not resized by this function.
@end deffn


@node Window Parameters
@section Window Parameters
@cindex window parameters

This section describes the window parameters that can be used to
associate additional information with windows.

@defun window-parameter window parameter
This function returns @var{window}'s value for @var{parameter}.  The
default for @var{window} is the selected window.  If @var{window} has no
setting for @var{parameter}, this function returns @code{nil}.
@end defun

@defun window-parameters &optional window
This function returns all parameters of @var{window} and their values.
The default for @var{window} is the selected window.  The return value
is either @code{nil}, or an association list whose elements have the form
@code{(@var{parameter} . @var{value})}.
@end defun

@defun set-window-parameter window parameter value
This function sets @var{window}'s value of @var{parameter} to
@var{value} and returns @var{value}.  The default for @var{window}
is the selected window.
@end defun

By default, the functions that save and restore window configurations
or the states of windows (@pxref{Window Configurations}) do not care
about window parameters.  This means that when you change the value of
a parameter within the body of a @code{save-window-excursion}, the
previous value is not restored when that macro exits.  It also means
that when you restore via @code{window-state-put} a window state saved
earlier by @code{window-state-get}, all cloned windows have their
parameters reset to @code{nil}.  The following variable allows you to
override the standard behavior:

@cindex persistent window parameters
@defvar window-persistent-parameters
This variable is an alist specifying which parameters get saved by
@code{current-window-configuration} and @code{window-state-get}, and
subsequently restored by @code{set-window-configuration} and
@code{window-state-put}.  @xref{Window Configurations}.

The @sc{car} of each entry of this alist is a symbol specifying the
parameter.  The @sc{cdr} should be one of the following:

@table @asis
@item @code{nil}
This value means the parameter is saved neither by
@code{window-state-get} nor by @code{current-window-configuration}.

@item @code{t}
This value specifies that the parameter is saved by
@code{current-window-configuration} and (provided its @var{writable}
argument is @code{nil}) by @code{window-state-get}.

@item @code{writable}
This means that the parameter is saved unconditionally by both
@code{current-window-configuration} and @code{window-state-get}.  This
value should not be used for parameters whose values do not have a read
syntax.  Otherwise, invoking @code{window-state-put} in another session
may fail with an @code{invalid-read-syntax} error.
@end table
@end defvar

Some functions (notably @code{delete-window},
@code{delete-other-windows} and @code{split-window}), may behave
specially when the window specified by their @var{window} argument has
a parameter whose name is equal to the function's name.  You can
override such special behavior by binding the following variable to a
non-@code{nil} value:

@defvar ignore-window-parameters
If this variable is non-@code{nil}, some standard functions do not
process window parameters.  The functions currently affected by this are
@code{split-window}, @code{delete-window}, @code{delete-other-windows},
and @code{other-window}.

An application can bind this variable to a non-@code{nil} value around
calls to these functions.  If it does so, the application is fully
responsible for correctly assigning the parameters of all involved
windows when exiting that function.
@end defvar

The following parameters are currently used by the window management
code:

@table @code
@item delete-window
@vindex delete-window@r{, a window parameter}
This parameter affects the execution of @code{delete-window}
(@pxref{Deleting Windows}).

@item delete-other-windows
@vindex delete-other-windows@r{, a window parameter}
This parameter affects the execution of @code{delete-other-windows}
(@pxref{Deleting Windows}).

@item no-delete-other-windows
@vindex no-delete-other-windows@r{, a window parameter}
This parameter marks the window as not deletable by
@code{delete-other-windows} (@pxref{Deleting Windows}).

@item split-window
@vindex split-window@r{, a window parameter}
This parameter affects the execution of @code{split-window}
(@pxref{Splitting Windows}).

@item other-window
@vindex other-window@r{, a window parameter}
This parameter affects the execution of @code{other-window}
(@pxref{Cyclic Window Ordering}).

@item no-other-window
@vindex no-other-window@r{, a window parameter}
This parameter marks the window as not selectable by @code{other-window}
(@pxref{Cyclic Window Ordering}).

@item clone-of
@vindex clone-of@r{, a window parameter}
This parameter specifies the window that this one has been cloned
from.  It is installed by @code{window-state-get} (@pxref{Window
Configurations}).

@item window-preserved-size
@vindex window-preserved-size@r{, a window parameter}
This parameter specifies a buffer, a direction where @code{nil} means
vertical and @code{t} horizontal, and a size in pixels.  If this window
displays the specified buffer and its size in the indicated direction
equals the size specified by this parameter, then Emacs will try to
preserve the size of this window in the indicated direction.  This
parameter is installed and updated by the function
@code{window-preserve-size} (@pxref{Preserving Window Sizes}).

@item quit-restore
@vindex quit-restore@r{, a window parameter}
This parameter is installed by the buffer display functions
(@pxref{Choosing Window}) and consulted by @code{quit-restore-window}
(@pxref{Quitting Windows}).  It is a list of four elements, see the
description of @code{quit-restore-window} in @ref{Quitting Windows}
for details.

@item window-side
@itemx window-slot
@vindex window-side@r{, a window parameter}
@vindex window-slot@r{, a window parameter}
These parameters are used internally for implementing side windows
(@pxref{Side Windows}).

@item window-atom
@vindex window-atom@r{, a window parameter}
This parameter is used internally for implementing atomic windows, see
@ref{Atomic Windows}.

@item mode-line-format
@vindex mode-line-format@r{, a window parameter}
This parameter replaces the value of the buffer-local variable
@code{mode-line-format} (@pxref{Mode Line Basics}) of this window's
buffer whenever this window is displayed.  The symbol @code{none} means
to suppress display of a mode line for this window.  Display and
contents of the mode line on other windows showing this buffer are not
affected.

@item header-line-format
@vindex header-line-format@r{, a window parameter}
This parameter replaces the value of the buffer-local variable
@code{header-line-format} (@pxref{Mode Line Basics}) of this window's
buffer whenever this window is displayed.  The symbol @code{none} means
to suppress display of a header line for this window.  Display and
contents of the header line on other windows showing this buffer are not
affected.

@item tab-line-format
@vindex tab-line-format@r{, a window parameter}
This parameter replaces the value of the buffer-local variable
@code{tab-line-format} (@pxref{Mode Line Basics}) of this window's
buffer whenever this window is displayed.  The symbol @code{none} means
to suppress display of a tab line for this window.  Display and
contents of the tab line on other windows showing this buffer are not
affected.

@item min-margins
@vindex min-margins@r{, a window parameter}
The value of this parameter is a cons cell whose @sc{car} and
@sc{cdr}, if non-@code{nil}, specify the minimum values (in columns)
for the left and right margin of this window (@pxref{Display Margins}.
When present, Emacs will use these values instead of the actual margin
widths for determining whether a window can be split or shrunk
horizontally.

Emacs never auto-adjusts the margins of any window after splitting or
resizing it.  It is the sole responsibility of any application setting
this parameter to adjust the margins of this window as well as those of
any new window that inherits this window's margins due to a split.
Both @code{window-configuration-change-hook} and
@code{window-size-change-functions} (@pxref{Window Hooks}) should be
employed for this purpose.

This parameter was introduced in Emacs version 25.1 to support
applications that use large margins to center buffer text within a
window and should be used, with due care, exclusively by those
applications.  It might be replaced by an improved solution in future
versions of Emacs.
@end table


@node Window Hooks
@section Hooks for Window Scrolling and Changes
@cindex hooks for window operations

This section describes how Lisp programs can take action after a
window has been scrolled or other window modifications occurred.  We
first consider the case where a window shows a different part of its
buffer.

@defvar window-scroll-functions
This variable holds a list of functions that Emacs should call before
redisplaying a window with scrolling.  Displaying a different buffer
in a window and making a new window also call these functions.

This variable is not a normal hook, because each function is called
with two arguments: the window, and its new display-start position.
At the time of the call, the display-start position of the argument
window is already set to its new value, and the buffer to be displayed
in the window is set as the current buffer.

These functions must take care when using @code{window-end}
(@pxref{Window Start and End}); if you need an up-to-date value, you
must use the @var{update} argument to ensure you get it.

@strong{Warning:} don't use this feature to alter the way the window
is scrolled.  It's not designed for that, and such use probably won't
work.
@end defvar

In addition, you can use @code{jit-lock-register} to register a Font
Lock fontification function, which will be called whenever parts of a
buffer are (re)fontified because a window was scrolled or its size
changed.  @xref{Other Font Lock Variables}.

@cindex window change functions
   The remainder of this section covers six hooks that are called
during redisplay provided a significant, non-scrolling change of a
window has been detected.  For simplicity, these hooks and the
functions they call will be collectively referred to as @dfn{window
change functions}.

@cindex window buffer change
The first of these hooks is run after a @dfn{window buffer change} is
detected, which means that a window was created, deleted or assigned
another buffer.

@defvar window-buffer-change-functions
This variable specifies functions called during redisplay when window
buffers have changed.  The value should be a list of functions that
take one argument.

Functions specified buffer-locally are called for any window showing
the corresponding buffer if that window has been created or assigned
that buffer since the last time window change functions were run.  In
this case the window is passed as argument.

Functions specified by the default value are called for a frame if at
least one window on that frame has been added, deleted or assigned
another buffer since the last time window change functions were run.
In this case the frame is passed as argument.
@end defvar

@cindex window size change
The second of these hooks is run when a @dfn{window size change} has
been detected which means that a window was created, assigned another
buffer, or changed its total size or that of its text area.

@defvar window-size-change-functions
This variable specifies functions called during redisplay when a
window size change occurred.  The value should be a list of functions
that take one argument.

Functions specified buffer-locally are called for any window showing
the corresponding buffer if that window has been added or assigned
another buffer or changed its total or body size since the last time
window change functions were run.  In this case the window is passed
as argument.

Functions specified by the default value are called for a frame if at
least one window on that frame has been added or assigned another
buffer or changed its total or body size since the last time window
change functions were run.  In this case the frame is passed as
argument.
@end defvar

@cindex window selection change
The third of these hooks is run when a @dfn{window selection change}
has selected another window since the last redisplay.

@defvar window-selection-change-functions
This variable specifies functions called during redisplay when the
selected window or a frame's selected window has changed.  The value
should be a list of functions that take one argument.

Functions specified buffer-locally are called for any window showing
the corresponding buffer if that window has been selected or
deselected (among all windows or among all windows on its frame) since
the last time window change functions were run.  In this case the
window is passed as argument.

Functions specified by the default value are called for a frame if
that frame has been selected or deselected or the frame's selected
window has changed since the last time window change functions were
run.  In this case the frame is passed as argument.
@end defvar

@cindex window state change
The fourth of these hooks is run when a @dfn{window state change} has
been detected, which means that at least one of the three preceding
window changes has occurred.

@defvar window-state-change-functions
This variable specifies functions called during redisplay when a
window buffer or size change occurred or the selected window or a
frame's selected window has changed.  The value should be a list of
functions that take one argument.

Functions specified buffer-locally are called for any window showing
the corresponding buffer if that window has been added or assigned
another buffer, changed its total or body size or has been selected or
deselected (among all windows or among all windows on its frame) since
the last time window change functions were run.  In this case the
window is passed as argument.

Functions specified by the default value are called for a frame if at
least one window on that frame has been added, deleted or assigned
another buffer, changed its total or body size or that frame has been
selected or deselected or the frame's selected window has changed
since the last time window change functions were run.  In this case
the frame is passed as argument.

Functions specified by the default value are also run for a frame when
that frame's window state change flag (see below) has been set since
last redisplay.
@end defvar

@cindex window configuration change
The fifth of these hooks is run when a @dfn{window configuration
change} has been detected which means that either the buffer or the
size of a window changed.  It differs from the four preceding hooks in
the way it is run.

@defvar window-configuration-change-hook
This variable specifies functions called during redisplay when either
the buffer or the size of a window has changed.  The value should be a
list of functions that take no argument.

Functions specified buffer-locally are called for any window showing
the corresponding buffer if at least one window on that frame has been
added, deleted or assigned another buffer or changed its total or
body size since the last time window change functions were run.  Each
call is performed with the window showing the buffer temporarily
selected and its buffer current.

Functions specified by the default value are called for each frame if
at least one window on that frame has been added, deleted or assigned
another buffer or changed its total or body size since the last time
window change functions were run.  Each call is performed with the
frame temporarily selected and the selected window's buffer current.
@end defvar

Finally, Emacs runs a normal hook that generalizes the behavior of
@code{window-state-change-functions}.

@defvar window-state-change-hook
The default value of this variable specifies functions called during
redisplay when a window state change has been detected or the window
state change flag has been set on at least one frame.  The value
should be a list of functions that take no argument.

Applications should put a function on this hook only if they want to
react to changes that happened on (or have been signaled for) two or
more frames since last redisplay.  In every other case, putting the
function on @code{window-state-change-functions} should be preferred.
@end defvar

Window change functions are called during redisplay for each frame as
follows: First, any buffer-local window buffer change function, window
size change function, selected window change and window state change
functions are called in this order.  Next, the default values for
these functions are called in the same order.  Then any buffer-local
window configuration change functions are called followed by functions
specified by the default value of those functions.  Finally, functions
on @code{window-state-change-hook} are run.

   Window change functions are run for a specific frame only if a
corresponding change was registered for that frame earlier.  Such
changes include the creation or deletion of a window or the assignment
of another buffer or size to a window.  Note that even when such a
change has been registered, this does not mean that any of the hooks
described above is run.  If, for example, a change was registered
within the scope of a window excursion (@pxref{Window
Configurations}), this will trigger a call of window change functions
only if that excursion still persists at the time change functions are
run.  If it is exited earlier, hooks will be run only if registered by
a change outside the scope of that excursion.

@cindex window state change flag
   The @dfn{window state change flag} of a frame, if set, will cause
the default values of @code{window-state-change-functions} (for that
frame) and @code{window-state-change-hook} to be run during next
redisplay regardless of whether a window state change actually
occurred for that frame or not.  After running any functions on these
hooks, the flag is reset for each frame.  Applications can set that
flag and inspect its value using the following functions.

@defun set-frame-window-state-change &optional frame arg
This function sets @var{frame}'s window state change flag if @var{arg}
is non-@code{nil} and resets it otherwise.  @var{frame} must be a live
frame and defaults to the selected one.
@end defun

@defun frame-window-state-change &optional frame
This functions returns @code{t} if @var{frame}'s window state change
flag is set and @code{nil} otherwise.  @var{frame} must be a live
frame and defaults to the selected one.
@end defun

   While window change functions are run, the functions described next
can be called to get more insight into what has changed for a specific
window or frame since the last redisplay.  All these functions take a
live window as single, optional argument, defaulting to the selected
window.

@defun window-old-buffer &optional window
This function returns the buffer shown in @var{window} at the last
time window change functions were run for @var{window}'s frame.  If it
returns @code{nil}, @var{window} has been created after that.  If it
returns @code{t}, @var{window} was not shown at that time but has been
restored from a previously saved window configuration afterwards.
Otherwise, the return value is the buffer shown by @code{window} at
that time.
@end defun

@defun window-old-pixel-width &optional window
This function returns the total pixel width of @var{window} the
last time window change functions found @code{window} live on its
frame.  It is zero if @code{window} was created after that.
@end defun

@defun window-old-pixel-height &optional window
This function returns the total pixel height of @var{window} the last
time window change functions found @code{window} live on its frame.
It is zero if @code{window} was created after that.
@end defun

@defun window-old-body-pixel-width &optional window
This function returns the pixel width of @var{window}'s text area the
last time window change functions found @code{window} live on its
frame.  It is zero if @code{window} was created after that.
@end defun

@defun window-old-body-pixel-height &optional window
This function returns the pixel height of @var{window}'s text area the
last time window change functions found @code{window} live on its
frame.  It is zero if @code{window} was created after that.
@end defun

In order to find out which window or frame was selected the last time
window change functions were run, the following functions can be used:

@defun frame-old-selected-window &optional frame
This function returns the selected window of @var{frame} at the last
time window change functions were run.  If omitted or @code{nil}
@var{frame} defaults to the selected frame.
@end defun

@defun old-selected-window
This function returns the selected window at the last time window
change functions were run.
@end defun

@defun old-selected-frame
This function returns the selected frame at the last time window
change functions were run.
@end defun

Note that window change functions provide no information about which
windows have been deleted since the last time they were run.  If
necessary, applications should remember any window showing a specific
buffer in a local variable of that buffer and update it in a function
run by the default values of any of the hooks that are run when a
window buffer change was detected.

   The following caveats should be considered when adding a function
to window change functions:

@itemize @bullet
@item
Some operations will not trigger a call of window change functions.
These include showing another buffer in a minibuffer window or any
change of a tooltip window.

@item
Window change functions should not create or delete windows or change
the buffer, size or selection status of any window because there is no
guarantee that the information about such a change will be propagated
to other window change functions.  If at all, any such change should
be executed only by the last function listed by the default value of
@code{window-state-change-hook}.

@item
Macros like @code{save-window-excursion}, @code{with-selected-window}
or @code{with-current-buffer} can be used when running window change
functions.

@item
Running window change functions does not save and restore match data.
Unless running @code{window-configuration-change-hook} it does not
save or restore the selected window or frame or the current buffer
either.

@item
Any redisplay triggering the run of window change functions may be
aborted.  If the abort occurs before window change functions have run
to their completion, they will be run again with the previous values,
that is, as if redisplay had not been performed.  If aborted later,
they will be run with the new values, that is, as if redisplay had
been actually performed.
@end itemize