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Document the lookbehind assertions (closing bug#115119)

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Andrew M. Kuchling 2000-10-05 15:22:28 +00:00
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commit 9351dd2084
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Doc/lib/libre.tex
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@ -219,6 +219,21 @@ is a negative lookahead assertion. For example,
\regexp{Isaac (?!Asimov)} will match \code{'Isaac~'} only if it's \emph{not}
followed by \code{'Asimov'}.
\item[\code{(?<=...)}] Matches if the current position in the string
is preceded by a match for \regexp{...} that ends at the current
position. This is called a positive lookbehind assertion.
\regexp{(?<=abc)def} will match \samp{abcdef}, since the lookbehind
will back up 3 characters and check if the contained pattern matches.
The contained pattern must only match strings of some fixed length,
meaning that \regexp{abc} or \regexp{a|b} are allowed, but \regexp{a*}
isn't.
\item[\code{(?<!...)}] Matches if the current position in the string
is not preceded by a match for \regexp{...}. This
is called a negative lookbehind assertion. Similar to positive lookbehind
assertions, the contained pattern must only match strings of some
fixed length.
\end{list}
The special sequences consist of \character{\e} and a character from the