code: function _processAnimations(event) {
          var prevItem;
          for (var i = 0; i < this._viewStack.length; i++) {
              var item = this._viewStack[i];
              switch (item.state) {
                  case ItemState.HIDE:
                      item.state = ItemState.HIDING;
                      _initHideAnimation.call(this, item, prevItem, event.size);
                      _updateState.call(this);
                      break;
                  case ItemState.SHOW:
                      item.state = ItemState.SHOWING;
                      _initShowAnimation.call(this, item, prevItem, event.size);
                      _updateState.call(this);
                      break;
              }
              prevItem = item;
          }
      }
docs: Starts a show or hide animation.