<boost/url/rfc/gen_delim_chars.hpp>
constexpr grammar::lut_chars gen_delim_chars = ":/?#[]@";
Character sets are used with rules and the functions grammar::find_if and grammar::find_if_not.
system::result< decode_view > rv = grammar::parse( "Program%20Files", pct_encoded_rule( gen_delim_chars ) );
gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@"