docs: function (item, component) {
              var key = this._getKeyForItem(item),
                  cacheItem = {
                      item: item,
                      component: component
                  };
              if (key) {
                  if (this.$renderedItemsMap[key]) {
                      this.$renderedItemsMap[key].push(cacheItem);
                  } else {
                      this.$renderedItemsMap[key] = [cacheItem];
                  }
              } else {
                  // add to rendered item map
                  this.$renderedItems.push(cacheItem);
              }
              return component;
          }