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