nt.detail.error and an
       * IronRequestElement is included in event.detail.request.
       *
       * @event iron-form-error
      */

      attached: function() {
        this._nodeObserver = Polymer.dom(this).observeNodes(
          function(mutations) {
            for (var i = 0; i < mutations.addedNodes.length; i++) {
              if (mutations.addedNodes[i].tagName === 'FORM' && !this._alreadyCalledInit) {
                this._alreadyCalledInit = true;
                this._form = mutations.adde