docs: function(options) {
          OpenLayers.Format.XML.prototype.initialize.apply(this, [options]);
          this.options = options;
          var yx = OpenLayers.Util.extend(
              {}, OpenLayers.Format.WMTSCapabilities.prototype.yx
          );
          this.yx = OpenLayers.Util.extend(yx, this.yx);
      }