/**
 * Add or Set the List Header
 * @method setHeader
 * @param {String} text - The header text
 */ 
setHeader: function (text) {
    if (typeof (text) == 'string') {
        var header = this._list.querySelectorAll('header');
        if (header) {
            if (header.length > 1) {
                // more than one <header> detected
                throw new Error("More than one <header> tag detected");
            }
            if (header.length == 1)
                header = header[0];
            else
                header = null;
        }

        if (!header) {
            header = document.createElement('header');
	    this._list.insertBefore(header, this._list.firstChild);
	}

        header.innerText = text;
    }
},