docs: function (className) {
              var document = this._document;
              var div = document.createElement("div");
              div.className = className || "xModalMask-default";
              div.style.cssText = "position:absolute;top:-15000px;left:-15000px;visibility:hidden;display:block;";
              return this.popupContainer.getContainerElt().appendChild(div);
          }