code: function(x, y, prevTileData){
              var tileData = this.getTileData(x, y, prevTileData);
              if(this.mergeWithPrevLayer && prevTileData){
                  return this.mergeTileData(prevTileData, tileData);
              }
              return tileData;
          }
docs: Get layer's `TileData` for a given map tile coord.
  Optionally modifying the `prevTileData` object param if `this.mergeWithPrevLayer = true`.
  @method getModifiedTileData
  @param {Number} x - Map tile x coord.
  @param {Object} y - Map tile y coord.
  @param {Object} [prevTileData] - `tileData` object for the given map tile coord from previous layer.
  @return {TileData|Bool} false if nothing to render