But that, Harm, is just the way SMIRF works. It asks the engine for a list
of valid moves and from that filters only valid move inputs from the user.
And that has been the basic idea of the TMCI protocol. The intended utmost
goal was to have some engines playing and a certified referee engine
secure a correct play of a chosen variant. That would make a GUI able to
communicate a family of games even unknown to it without any need to be
changed or updated. Therefore the base of its communication: X-FEN has to
be maximally independent from any selectable variant. The subset of
variants it aimed to cover has been called: FullChess.
