GNU bug report logs - #192
regexp does not work as documented

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From: martin rudalics <rudalics <at> gmx.at>
To: David Koppelman <koppel <at> ece.lsu.edu>
Cc: Chong Yidong <cyd <at> stupidchicken.com>, 192 <at> debbugs.gnu.org,
        Bruno Haible <bruno <at> clisp.org>, emacs-devel <at> gnu.org
Subject: bug#192: regexp does not work as documented
Date: Sun, 11 May 2008 09:40:51 +0200

> First I'll work on the hi-lock warning as I described below, then I'll
> see about detecting and doing something helpful for additional
> situations where multi-line won't work.

Think of the following pathological case: Devise a regexp to highlight
the first line of a buffer provided the buffer does not end with a
newline.  Doing this with `font-lock-multiline' hardly makes any sense.

Maybe users should classify whether a regexp they use

(1) doesn't match newlines - no `font-lock-multiline' needed,

(2) match at most n newlines in which case you should tell font-lock to
rescan from n lines before each buffer change (with large n the display
engine will suffer noticeably, mainly because font-lock has to search
for all other keywords as well), or

(3) may match more than n newlines in which case you should use an idle
timer to scan the entire buffer for any matches of such regexps and
highlight them separately.

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