code: function(evt) {
          var tile = evt.object;
          var img = this.tileCache[tile.url];
          if (img) {
            // if image is on its layer's backbuffer, remove it from backbuffer
            if (img.parentNode &&
                    OpenLayers.Element.hasClass(img.parentNode, 'olBackBuffer')) {
                img.parentNode.removeChild(img);
                img.id = null;
            }
            // only use image from cache if it is not on a layer already
            if (!img.parentNode) {
                img.style.visibility = 'hidden';
                img.style.opacity = 0;
                tile.setImage(img);
                // LRU - move tile to the end of the array to mark it as the most
                // recently used
                OpenLayers.Util.removeItem(this.tileCacheIndex, tile.url);
                this.tileCacheIndex.push(tile.url);
            }
          }
      }
docs: Method: manageTileCache
  Adds, updates, removes and fetches cache entries.
  
  Parameters:
  evt - {Object} Listener argument of the tile's beforeload event