The unreserved character set
const lut_chars unreserved_chars ;
Declared in file <boost/url/rfc/unreserved_chars.hpp> at line 44
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( unreserved_chars ) );
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"