boost::xpressive::range — Match a range of characters.
// In header: <boost/xpressive/regex_primitives.hpp> template<typename Char> unspecified range(Char ch_min, Char ch_max);
Match any character in the range [ch_min, ch_max].
Parameters:
ch_max
The upper end of the range to match.
ch_min
The lower end of the range to match.