boost::urls::grammar::ref

template<CharSet CS>
constexpr
/* implementation-defined */
ref(CS const& cs) noexcept
requires is_charset<CS>::value &&
    ! std::is_same<CS,
        implementation_defined::charset_ref<CS> >::value;

template<Rule R>
constexpr
/* implementation-defined */
ref(R const& r) noexcept
requires is_rule<R>::value &&
    ! std::is_same<R,
        implementation_defined::rule_ref<R> >::value;