code: function(evt) {
          if (this.active && !evt.aborted &&
                  evt.tile instanceof OpenLayers.Tile.Image &&
                  evt.tile.url.substr(0, 5) !== 'data:') {
              this.cache({tile: evt.tile});
              delete OpenLayers.Control.CacheWrite.urlMap[evt.tile.url];
          }
      }
docs: Method: onTileLoaded
  Decides whether a tile can be cached and calls the cache method.
  
  Parameters:
  evt - {Event}