docs: function () {
                  var openedPopups = this.openedPopups;
                  var topPopup = null;
                  if (openedPopups.length > 0) {
                      topPopup = openedPopups[openedPopups.length - 1];
                      var topZIndex = topPopup.getZIndex();
                      for (var i = openedPopups.length - 2; i >= 0; i--) {
                          var curPopup = openedPopups[i];
                          var curZIndex = curPopup.getZIndex();
                          if (curZIndex > topZIndex) {
                              topPopup = curPopup;
                              topZIndex = curZIndex;
                          }
                      }
                  }
                  return topPopup;
              }