allowed when using the Perl regular expression syntax. This change has
been added for Perl compatibility, when the new [syntax_option_type]
['no_empty_expressions] is set then the old behaviour is preserved and
empty expressions are prohibited. This is issue
[@https://svn.boost.org/trac/boost/ticket/1081#1081].
Fixes#1081.
[SVN r50374]
Add optional support for marked sub-expression location information.
Add support for ${n} in format replacement text.
Fixes#2556.
Fixes#2269.
Fixes#2514.
[SVN r50370]
2) Changed std::copy calls on VC8 to avoid "dangerous code" warnings.
3) Moved backreference and octal escape code into line with POSIX-extended requirements.
4) Changed match_results leftmost-longest rules to stop unnecessary std::distance computations (an optimisation for non-random access iterators).
5) Changed C lib calls to use "safe" versions of string API's where available.
6) Added many new POSIX-extended leftmost-longest tests, to verify the above.
[SVN r27880]
