Rule for URI-reference
<include/boost/url/rfc/uri_reference_rule.hpp>
constexpr
_implementation-defined_ uri_reference_rule = {};
using value_type = url_view;
system::result< url_view > rv = grammar::parse( "ws://echo.example.com/?name=boost#demo", uri_reference_rule );
URI-reference = URI / relative-ref
URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
relative-ref = relative-part [ "?" query ] [ "#" fragment ]