code: public synchronized void storeMapItems(Tile tile, List<MapElementContainer> mapItems) {
          this.put(tile, LayerUtil.collisionFreeOrdered(mapItems));
          this.version += 1;
      }
docs: Stores a list of MapElements against a tile.
  
  @param tile     tile on which the mapItems reside.
  @param mapItems the map elements.