docs: function OptionManager(api) {
  
      /**
       * @private
       * @type {module:echarts/ExtensionAPI}
       */
      this._api = api;
  
      /**
       * @private
       * @type {Array.<number>}
       */
      this._timelineOptions = [];
  
      /**
       * @private
       * @type {Array.<Object>}
       */
      this._mediaList = [];
  
      /**
       * @private
       * @type {Object}
       */
      this._mediaDefault;
  
      /**
       * -1, means default.
       * empty means no media.
       * @private
       * @type {Array.<number>}
       */
      this._currentMediaIndices = [];
  
      /**
       * @private
       * @type {Object}
       */
      this._optionBackup;
  
      /**
       * @private
       * @type {Object}
       */
      this._newBaseOption;
  }