tmac/troffrc{,-end}: Improve style.

Follow established idioms and make them consistent with each other.

* tmac/troffrc:
* tmac/troffrc-end:
  + Identify files in header comments as part of GNU troff.

* tmac/troffrc:
  + Clarify purpose of .do request.
  + Identify .X (set by groff -X) as a register, not a string.
  + Remove temporary registers one per line to make
    synchronization with foregoing logic easier.  Fixes name
    space management nits: an undefined string troffrc!Xps was
    being removed, and troffrc!{ascii,latin1,utf8,cp1047} were
    not being removed despite being defined.

* tmac/troffrc-end:
  + Clarify that file is read after -m file arguments (not "all
    macro sets", which can be loaded with .mso after this file
    is processed).
  + Advise usage of .do for groff extensions.
  + Line-break one-off conditionals as troffrc does.
  + Add empty string comment to empty string definitions.
  + Add editor configuration comments.

1 files changed, 29 insertions, 23 deletions

diff --git a/tmac/troffrc-end b/tmac/troffrc-end
index e8a3ba65b..41b4400df 100644
--- a/tmac/troffrc-end
+++ b/tmac/troffrc-end
@@ -1,28 +1,34 @@
-.\" -*- nroff -*-
+.\" final startup file for GNU troff
 .\"
-.\" final startup file for troff
-.
-.\" this file is parsed after all macro sets have been read
+.\" This file is parsed after all -m file arguments have been read.
+.\"
+.\" Use .do for any groff extensions so that this file works with -C.
 .
-.do if '\*[.T]'html' .do mso html-end.tmac
+.do if '\*[.T]'html' \
+.	do mso html-end.tmac
 .
-.\" if we are running the postscript device for html images then load www.tmac
-.do if r ps4html     .do mso www.tmac
+.\" Load www if we are running the PostScript driver for HTML images.
+.do if r ps4html \
+	.do mso www.tmac
 .
-.\" for all other devices blank out these macros
-.do if !d HTML-IMAGE-INLINE      .do ds HTML-IMAGE-INLINE
-.do if !d HTML-IMAGE             .do ds HTML-IMAGE
-.do if !d HTML-IMAGE-RIGHT       .do ds HTML-IMAGE-RIGHT
-.do if !d HTML-IMAGE-LEFT        .do ds HTML-IMAGE-LEFT
-.do if !d HTML-IMAGE-END         .do ds HTML-IMAGE-END
-.do if !d DEVTAG                 .do ds DEVTAG
-.do if !d HTML-DO-IMAGE          .do ds HTML-DO-IMAGE
-.do if !d EQN-HTML-IMAGE-END     .do ds EQN-HTML-IMAGE-END
-.do if !d EQN-HTML-IMAGE         .do ds EQN-HTML-IMAGE
-.do if !d EQN-HTML-IMAGE-RIGHT   .do ds EQN-HTML-IMAGE-RIGHT
-.do if !d EQN-HTML-IMAGE-LEFT    .do ds EQN-HTML-IMAGE-LEFT
-.do if !d EQN-HTML-IMAGE-INLINE  .do ds EQN-HTML-IMAGE-INLINE
-.do if !d EQN-HTML-DO-IMAGE      .do ds EQN-HTML-DO-IMAGE
-.do if !d EQN-HTML-IMAGE-END     .do ds EQN-HTML-IMAGE-END
+.\" For all other devices, make these macros no-ops.
+.do if !d HTML-IMAGE-INLINE      .do ds HTML-IMAGE-INLINE \" empty
+.do if !d HTML-IMAGE             .do ds HTML-IMAGE \" empty
+.do if !d HTML-IMAGE-RIGHT       .do ds HTML-IMAGE-RIGHT \" empty
+.do if !d HTML-IMAGE-LEFT        .do ds HTML-IMAGE-LEFT \" empty
+.do if !d HTML-IMAGE-END         .do ds HTML-IMAGE-END \" empty
+.do if !d DEVTAG                 .do ds DEVTAG \" empty
+.do if !d HTML-DO-IMAGE          .do ds HTML-DO-IMAGE \" empty
+.do if !d EQN-HTML-IMAGE-END     .do ds EQN-HTML-IMAGE-END \" empty
+.do if !d EQN-HTML-IMAGE         .do ds EQN-HTML-IMAGE \" empty
+.do if !d EQN-HTML-IMAGE-RIGHT   .do ds EQN-HTML-IMAGE-RIGHT \" empty
+.do if !d EQN-HTML-IMAGE-LEFT    .do ds EQN-HTML-IMAGE-LEFT \" empty
+.do if !d EQN-HTML-IMAGE-INLINE  .do ds EQN-HTML-IMAGE-INLINE \" empty
+.do if !d EQN-HTML-DO-IMAGE      .do ds EQN-HTML-DO-IMAGE \" empty
+.do if !d EQN-HTML-IMAGE-END     .do ds EQN-HTML-IMAGE-END \" empty
 .
-.\" Don't let blank lines creep in here.
+.\" Local Variables:
+.\" mode: nroff
+.\" fill-column: 72
+.\" End:
+.\" vim: set filetype=groff textwidth=72: