 element.
     */
    get inputElement() {
      return this.$.input;
    },

    /**
     * Returns a reference to the focusable element.
     */
    get _focusableElement() {
      return this.inputElement;
    },

    attached: function() {
      this._updateAriaLabelledBy();
    },

    _appendStringWithSpace: function(str, more) {
      if (str) {
        str = str + ' ' + more;
      } else {
        str = more;
      }
      return str;
    },

    _onAddonAttached: function(event) {
      var target