Single Comment

This code would actually do it:

function F() {
  if(document.getElementsByName('pastmoves').length == 0) return;
  if(legalMoves) {
    var ori = legalMoves[0][0], n = legalMoves.length - 1, t = '';
    if(legalMoves[n][0] == 'movetext') t = legalMoves[n--][1], legalMoves.pop();
    for(var i=n; i>0; i--) if(legalMoves[i][0] != ori) break;
    if(!i) {
      movePiece(ori);
      if(t != '') document.getElementById('movesfield').value = t;
    }
  }
}
setTimeout("F()", 100);

This would allow the GAME code to abuse the $legalmoves array to pass an arbitrary text xxx for the movefield in the continuemove form, by adding a 'move' ("movetext" "xxx") as the last element. The JavaScript would then clip that off, and place it in the move field, after selecting the only piece at the origin of all remaining moves to highlight its targets. These moves would also be fakes, as it is not really this piece that is going to move, as you would be preparing for the entry of a suicide of freedrop, which only require a destination. So the mentioned origin is just a dummy. The fake 'movetext move' cannot be added using setlegal, as the latter would test its arguments for being valid square names. But it can be added by assigning directly to $legalmoves.

BTW, there is no formal description of setlegal in the GAME-code manual.