code: function (observer) {
              var observers = this.observers, i;
              for (i = observers.length - 1; i >= 0; --i) {
                  /*
               If multiple identical EventListeners are registered on the same EventTarget
               with the same parameters the duplicate instances are discarded.
               They do not cause the EventListener to be called twice
               and since they are discarded
               they do not need to be removed with the removeEventListener method.
               */
                  if (observer.equals(observers[i])) {
                      return i;
                  }
              }
              return -1;
          }
docs: Search for a specified observer within current event's observers
  @param {KISSY.Event.Observer} observer
  @return {Number} observer's index in observers