code: function SubmenuPlugin(selectivity, options) {
      /**
       * Optional parent dropdown menu from which this dropdown was opened.
       */
      this.parentMenu = options.parentMenu;
  
      Dropdown.call(this, selectivity, options);
  
      this._closeSubmenuTimeout = 0;
  
      this._openSubmenuTimeout = 0;
  }
docs: Extended dropdown that supports submenus.