permutation operator ^ absent

[alfC]

...in X3.

Is it not fundamental or lightweight? Is there an obvious way that permutation can be implemented by the user? (I don't know enough about grammars to tell)

x3::phrase_parse(
            str.begin(), str.end(),
                (x3::lit("a") >> '=' >> x3::double_)
                ^
                (x3::lit("b") >> '=' >> x3::double_) 
            ,
            x3::space,
            ab
);

Currently I am doing phrase_parse( ..., *( (x3::lit("a") >> "=" >> x3::double_)[action] | (x3::lit("b") >> "=" >> x3::double_)[action] ) ...) but I think it is not the same.