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* etc/PROBLEMS: Mention problems with regexp matcher. (Bug#18577)

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Stefan Kangas 2021-10-24 23:56:46 +02:00
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etc/PROBLEMS
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@ -742,6 +742,18 @@ completed" message that tls.el relies upon, causing affected Emacs
functions to hang. To work around the problem, use older or newer
versions of gnutls-cli, or use Emacs's built-in gnutls support.
*** Stack overflow in regexp matcher.
Due to fundamental limitations in the way Emacs' regular expression
engine is designed, you might run into combinatorial explosions in
backtracking with certain regexps.
Avoid "\(...\(...\)*...\)*" and "\(...\)*\(...\)*". Look for a way to
anchor your regular expression, to avoid matching the null string in
infinite ways. The latter is what creates backtrack points, and
eventual overflow in practice.
(Also prefer "\(?:...\)" to "\(...\)" unless you need the latter.)
* Runtime problems related to font handling
** Characters are displayed as empty boxes or with wrong font under X.