boost_1_45_0/libs/regex/doc/leftmost_longest.qbk

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  Copyright 2006-2007 John Maddock.
  Distributed under the Boost Software License, Version 1.0.
  (See accompanying file LICENSE_1_0.txt or copy at
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[section:leftmost_longest_rule The Leftmost Longest Rule]

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:

# Find the leftmost match, if there is only one match possible at 
this location then return it.
# Find the longest of the possible matches, along with any ties.  
If there is only one such possible match then return it.
# If there are no marked sub-expressions, then all the remaining 
alternatives are indistinguishable; return the first of these found.
# 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.
# 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.
# Repeat steps 4 and 5 for each additional marked sub-expression.
# If there is still more than one possible match remaining, then they are 
indistinguishable; return the first one found.

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