Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Global lower

boost::xpressive::lower — Matches a lower-case character.

unspecified lower;

The regex traits are used to determine which characters are lower-case. To match any character that is not a lower-case character, use ~lower.