-Ambiguous chess
-https://www.chessvariants.com/mvopponent.dir/ambiguous-chess.html
-Need special highlight square --> similar to enlightened for Dark, in Board.vue
-Also in notation, show only dest square for "opponents ambiguous moves".
-Similar to Marseille-chess, white first move only 1 subTurn, do not choose a square.
-Then black has a free first move, then choose a square, and the process goes on.
+Merge variants 1, 2 (3) into one with sub-variant selection when starting a game (New Game + vs engine + analyse)
+E.g. Checkered 1 & 2 into one, and so on.
+Need additional field in variant code... in a generic way (radiobutton or select or checkbox?)