Or we could introduce a special XBetza notation for virgin moves that cannot be played when in check
If that's the chosen option, it seems like it'd make sense to expand it to any move that can't be made while in check — see, for instance, David Cannon's Lemniscate Chess where a checked king can't move at all. (That variant in particular is probably well out of scope for the applet, but similar rules are concievable for other more mobile kings as an alternative to excluding movement through check)
If that's the chosen option, it seems like it'd make sense to expand it to any move that can't be made while in check — see, for instance, David Cannon's Lemniscate Chess where a checked king can't move at all. (That variant in particular is probably well out of scope for the applet, but similar rules are concievable for other more mobile kings as an alternative to excluding movement through check)