nu is opened
         * and closed multiple times.
         *
         * @attribute stickySelection
         * @type boolean
         * @default false
         */
        stickySelection: false,

        /**
         * The index of the selected menu item.
         * @attribute selected
         * @type number
         */
        selected: '',

        /**
         * Specifies the attribute to be used for "selected" attribute.
         *
         * @attribute valueattr
         * @type string
         * @def