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| -rw-r--r-- | ChangeLog | 4 | ||||
| -rw-r--r-- | doc/groff.texinfo | 38 |
2 files changed, 41 insertions, 1 deletions
@@ -1,3 +1,7 @@ +2010-05-01 Werner LEMBERG <wl@gnu.org> + + * doc/groff.texinfo: Improve documentation of \R escape. + 2010-03-10 Werner LEMBERG <wl@gnu.org> * doc/groff.texinfo: Document \n[DD] register. diff --git a/doc/groff.texinfo b/doc/groff.texinfo index de877156..dafbc768 100644 --- a/doc/groff.texinfo +++ b/doc/groff.texinfo @@ -5971,7 +5971,6 @@ The argument to @code{\R} usually has to be enclosed in quotes. The @code{\R} escape doesn't produce an input token in @code{gtroff}; in other words, it vanishes completely after @code{gtroff} has processed it. -@endDefreq For example, the following two lines are equivalent: @@ -5981,6 +5980,43 @@ For example, the following two lines are equivalent: @result{} 1 @endExample +Note that the complete transparency of @code{\R} can cause surprising +effects if you use number registers like @code{.k} which get evaluated +at the time they are accessed. + +@Example +.ll 1.6i +. +aaa bbb ccc ddd eee fff ggg hhh\R':k \n[.k]' +.tm :k == \n[:k] + @result{} :k == 126950 +. +.br +. +aaa bbb ccc ddd eee fff ggg hhh\h'0'\R':k \n[.k]' +.tm :k == \n[:k] + @result{} :k == 15000 +@endExample + +If you process this with the PostScript device (@code{-Tps}), there +will be a line break eventually after @code{ggg} in both input lines. +However, after processing the space after @code{ggg}, the partially +collected line is not overfull yet, so @code{troff} continues to +collect input until it sees the space (or in this case, the newline) +after @code{hhh}. At this point, the line is longer than the line +length, and the line gets broken. + +In the first input line, since the @code{\R} escape leaves no traces, +the check for the overfull line hasn't been done yet at the point where +@code{\R} gets handled, and you get a value for the @code{.k} number +register which is even greater than the current line length. + +In the second input line, the insertion of @code{\h'0'} to emit an +invisible zero-width space forces @code{troff} to check the line length +which in turn causes the start of a new output line. Now @code{.k} +returns the expected value. +@endDefreq + Both @code{nr} and @code{\R} have two additional special forms to increment or decrement a register. |