code: function(evt) {
          if (evt.tile instanceof OpenLayers.Tile.Image) {
              evt.tile.events.on({
                  beforedraw: this.queueTileDraw,
                  beforeload: this.manageTileCache,
                  loadend: this.addToCache,
                  unload: this.unloadTile,
                  scope: this
              });        
          } else {
              // Layer has the wrong tile type, so don't handle it any longer
              this.removeLayer({layer: evt.tile.layer});
          }
      }
docs: Method: addTile
  Listener for the layer's addtile event
  
  Parameters:
  evt - {Object} The listener argument