code: function (bounds) {
          var xyz = this.getXYZ(bounds);
          var url = this.url;
          if (OpenLayers.Util.isArray(url)) {
              var s = '' + xyz.x + xyz.y + xyz.z;
              url = this.selectUrl(s, url);
          }
          
          return OpenLayers.String.format(url, xyz);
      }
docs: Method: getURL
  
  Parameters:
  bounds - {<OpenLayers.Bounds>}
  
  Returns:
  {String} A string with the layer's url and parameters and also the
  passed-in bounds and appropriate tile size specified as
  parameters