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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
- http://www.boost.org/LICENSE_1_0.txt).
- ]
- [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.
- [endsect]
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