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<H1 align="center">Boost.Regex</H1>
<H2 align="center">The "Leftmost Longest" Rule</H2>
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<p></p>
<P>Often there is more than one way of matching a regular expression at a
particular location, for POSIX basic and extended regular expressions, the
"best" match is determined as follows:</P>
<OL>
<LI>
Find the leftmost match, if there is only one match possible at this location
then return it.</LI>
<LI>
Find the longest of the possible matches, along with any ties. If there
is only one such possible match then return it.</LI>
<LI>
If there are no marked sub-expressions, then all the remaining alternatives are
indistinguishable; return the first of these found.</LI>
<LI>
Find the match which has matched the first sub-expression in the leftmost
position, along with any ties. If there is only on such match possible
then return it.</LI>
<LI>
Find the match which has the longest match for the first sub-expression, along
with any ties. If there is only one such match then return it.</LI>
<LI>
Repeat steps 3 and 4 for each additional marked sub-expression.</LI>
<LI>
If there is still more than one possible match remaining, then they are
indistinguishable; return the first one found.</LI></OL>
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<P></P>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
16 Dec 2004</p>
<p><i> Copyright John Maddock 1998-
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%Y" startspan --> 2003<!--webbot bot="Timestamp" endspan i-checksum="39359" --></i></p>
<P><I>Use, modification and distribution are subject to the Boost Software License,
Version 1.0. (See accompanying file <A href="../../../LICENSE_1_0.txt">LICENSE_1_0.txt</A>
or copy at <A href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>)</I></P>
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