docs: function (x, y, z, obj) {
              var pos = this.pos2px(x,y);
              pos.top -= z * (this._tile.width / 2);
              obj.attr({
                  x: pos.left + Crafty.viewport._x, 
                  y: pos.top + Crafty.viewport._y
              }).z += z;
              return this;
          }