I just noticed while working on Emacs's whitespace.el that Emacs’s syntax
coloring does not color the sequence “\\{” specially in a string, though it
recognises other regexp metacharacters such as “\\(”.I looked in the Emacs manuals, and found no mention of braces as a special character, despite the fact that they’re already used in whitespace-space-after-tab-regexp, for example; and of course, when I looked in the source code, I found the support there, as one would expect, in src/regex.c. The definitive documentation for the GNU regex implementation, as far as I know, is in gnulib’s doc/regex.texi, but as that file says: We wrote this chapter with programmers in mind, not users of programs---such as Emacs---that use Regex. We describe the Regex library in its entirety, not how to write regular expressions that a particular program understands. Since the regexp code is widely used, with mechanically-defined syntax variants, in GNU grep, GNU sed etc., it would seem possible to have a mechanically-generated manual, which takes a set of GNU regexp syntax flags, as taken by re_set_syntax, and spits out suitably-configured documentation. This could be either incorporated into other programs' manuals, or, perhaps better, supplied as standalone info files and man pages, suitable for cross-referencing from other programs' manuals, rather like a user-level version of the current gnulib/regex.texi. In principle it would be possible to compile a manual for every possible syntax variant, but in practice I imagine one would want to supply one for POSIX BREs and EREs, GNU-extended EREs (i.e. GNU egrep syntax) and Emacs. -- http://rrt.sc3d.org
