docs: function (pos) {
          var layerSize = this.layerSize,
              tiles = this.tiles
  
          if (pos.x < 0 || pos.y < 0 || pos.x >= layerSize.width || pos.y >= layerSize.height) {
              throw "TMX Layer: Invalid position"
          }
  
          var tile,
              gid = this.tileGIDAt(pos)
  
          // if GID is 0 then no tile exists at that point
          if (gid) {
              var z = pos.x + pos.y * layerSize.width
              tile = this.getChild({tag: z})
          }
  
          return tile
      }