anchor.diff:  abstract class Monster extends Occupant {
       Monster(DungeonState ds) : super(ds);
       Action takeTurn();
  +}
  +
  +abstract class CellMarker {
  +    void drawOnCell(CanvasRenderingContext2D ctx,
  +                    num bx0, num by0, num bxlen, num bylen);
  +}
  +
  +class TombStone {
  +    void drawOnCell(CanvasRenderingContext2D ctx,
  +                      num bx0, num by0, num bxlen, num bylen) {
  +
  +        var x = bx0 + bxlen/2;
  +        var y = by0 + bylen;
  +
  +        ctx.fillStyle = "#cd0000";
  +        ctx.fillStyle = "gray";
  +        ctx.textAlign = "center";
  +        ctx.textBaseline = "bottom";
  +        ctx.font = "37pt Calibri";
  +        // ctx.fillText("\u{2620}", x, y);
  +        ctx.fillText("@", x, y);
  +        ctx.fillText("/", x, y);
  +        ctx.fillText("\\", x, y);
  +    }
   }
   
   class Zombie extends Monster {
  
positive.code: // x status text
  
  void main() {
      startDungeon();
      ButtonElement button = querySelector('#reset');
      button.onClick.listen( (e) {
          startDungeon();
      });
  }
  
negative.code:                       num bx0, num by0, num bxlen, num bylen) {
  
          var x = bx0 + bxlen/2;
          var y = by0 + bylen;
  
          if (hit) {
              ctx.fillStyle = "#cd0000";
          } else if (active) {
              ctx.fillStyle = "black";
          } else {
              ctx.fillStyle = "#adadad";
          }
          ctx.textAlign = "center";
          ctx.textBaseline = "bottom";
          ctx.font = "37pt Calibri";
          ctx.fillText("z", x, y);
      }
  
     String toString() { return "Zombie";}
  }
  
  
  