docs: function _createForeground(node) {
          this._foreground = {
              surface: new Surface({
                  size: this.options.size,
                  properties: {
                      backgroundColor: this.options.pullToRefreshBackgroundColor
                  }
              }),
              mod: new Modifier({})
          };
          node.add(this._foreground.mod).add(this._foreground.surface);
      }