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 cntrl

boost::xpressive::cntrl — Matches a control character.

unspecified cntrl;

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