<boost/url/grammar/alnum_chars.hpp>
constexpr /* implementation-defined */ alnum_chars = {};
Character sets are used with rules and the functions find_if
and find_if_not
.
system::result< core::string_view > = parse( "Johnny42", token_rule( alnumchars ) );
ALNUM = ALPHA / DIGIT
ALPHA = %x41-5A / %x61-7A
; A-Z / a-z
DIGIT = %x30-39
; 0-9