 type: Object,
          value: function() { return {}; }
        },
        /**
        * Set the `withCredentials` flag on the request. See PolymerElements/iron-ajax for
        * more details. Only works when `allowRedirect` is false.
        */
        withCredentials: {
          type: Boolean,
          value: false
        },
      },
      /**
       * Fired if the form cannot be submitted because it's invalid.
       *
       * @event iron-form-invalid
       */

      /**
       * Fired after the 