docs: function(preloaderUrl, options, task, callback) {
              var popup = this.showPopup(preloaderUrl, options);
              this.$stage.$window.focus();
  
              if (task) {
                  try {
                      task(popup, function (err, url) {
                          popup.focus();
  
                          if (err) {
                              popup.close();
                          } else if (url) {
                              popup.location = url;
                          }
  
                          callback && callback(err);
                      });
                  } catch (e) {
                      callback && callback(e);
                  }
              } else {
                  callback && callback(new Error("No task specified"));
              }
          }