>>Does that answer the question ?
>
>IMO, it does not - it's the full list of how passing parameters in Fox works, from the caller's side. What we need here is the callee side, where I don't know of a way to distinguish between a passed value and a passed reference. Either way, the callee receives a pointer to a memory block where the value resides; it's the actual status of the value (is it a value of a variable, or a copy of a value assigned to a parameter) that I don't see how to distinguish, without knowing Fox source code.

Yes, exactly - I don't see a way and doubt there is one.