| [/ |
| 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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