anchor.diff:          //window.console.debug("draw square: " + p.toString());
   
           var sq = grid.getSquare(p);
  +        if (sq.isMarked()) {
  +            sq.marker.drawOnCell(ctx, x, y, boxDimX, boxDimX);
  +        }
           if (sq.isOccupied()) {
               //window.console.debug("draw cell");
               sq.occupant.drawOnCell(ctx, x, y, boxDimX, boxDimX);
  
positive.code: }
  
  enum Input {
      Up, Down, Left, Right
  }
  
  // A dungeon grid
  
negative.code: 
      String toString() {
          return "GridPont(" + x.toString() + "," + y.toString() + ")";
      }
  
      String toSimpleString() {
          return "(" + x.toString() + "," + y.toString() + ")";
      }
  
      int get hashCode {
  