anchor.diff:  
       final Coord newHead = headCoord.copy();
       assert(newHead != null);
  -    print("length = ${coords.length}");
  +
       newHead.add(direction);
   
  -    print("head.x = ${newHead.x} head.y=${newHead.y}");
       if (!isOnCanvas(newHead)) {
         collisionWithCanvas();
         return;
  
positive.code:     points += delta;
    }
  
    void showData() {
      showPoints();
      showDirection();
    }
  
    void showPoints() {
      var pts = querySelector("#points");
  
negative.code:   int maxSize = 3;
    List<Coord> coords = new List();
  
    // XXX These coordinates do not belong here.  Only the
    //     snake-coordinates belong here, canvas should completely
    //     elsewhere.
    int cwidth;
    int cheight;
  
  