docs: function (eventType, callback, scope) {
                  if (!eventType) {
                      // remove all events
                      this._eventHandlers = {};
                  } else if (!callback) {
                      // remove all callbacks for these event
                      this._eventHandlers[eventType] = [];
                  } else if (this._eventHandlers[eventType]) {
                      var list = this._eventHandlers[eventType];
                      for (var i = list.length - 1; i >= 0; i--) {
                          if (list[i].$callback == callback && (!scope || scope === list[i].scope)) {
                              list.splice(i, 1);  // delete callback
                          }
                      }
                  }
              }