...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::algorithm::is_classified — is_classified predicate
// In header: <boost/algorithm/string/classification.hpp> unspecified is_classified(std::ctype_base::mask Type, const std::locale & Loc = std::locale());