boost::xpressive::alnum — Matches an alpha-numeric character.
// In header: <boost/xpressive/regex_primitives.hpp> unspecified alnum;
The regex traits are used to determine which characters are alpha-numeric. To match any character that is not alpha-numeric, use ~alnum.
alnum is equivalent to /[[:alnum:]]/ in perl. ~alnum is equivalent to /[[:^alnum:]]/ in perl.
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