[#EFD205C2FD02E34A0FAE1B9CA2ED6E03A0C2D512]
A set of characters
class lut_chars;
The characters defined by instances of this set are provided upon construction. The `constexpr` implementation allows these to become compile-time constants.
Character sets are used with rules and the functions find_if and find_if_not .
constexpr lut_chars vowel_chars = "AEIOU" "aeiou";
system::result< core::string_view > rv = parse( "Aiea", token_rule( vowel_chars ) );