From 5bcc933211a880d17341082644122c75e29e17c2 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Wed, 10 Sep 2003 18:45:12 +0000 Subject: [PATCH] SF bug #803842: Wrong description of regexp concatenation --- Doc/lib/libre.tex | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/Doc/lib/libre.tex b/Doc/lib/libre.tex index 1aaebd9584d..7368ab47144 100644 --- a/Doc/lib/libre.tex +++ b/Doc/lib/libre.tex @@ -51,10 +51,11 @@ matches a particular string, which comes down to the same thing). Regular expressions can be concatenated to form new regular expressions; if \emph{A} and \emph{B} are both regular expressions, -then \emph{AB} is also a regular expression. If a string \emph{p} -matches A and another string \emph{q} matches B, the string \emph{pq} -will match AB if \emph{A} and \emph{B} do no specify boundary -conditions that are no longer satisfied by \emph{pq}. Thus, complex +then \emph{AB} is also a regular expression. In general, if a string +\emph{p} matches \emph{A} and another string \emph{q} matches \emph{B}, +the string \emph{pq} will match AB. This holds unless \emph{A} or +\emph{B} contain low precedence operations; boundary conditions between +\emph{A} and \emph{B}; or have numbered group references. Thus, complex expressions can easily be constructed from simpler primitive expressions like the ones described here. For details of the theory and implementation of regular expressions, consult the Friedl book