&& this._useValue(el)) {
          addSerializedElement(el.name, el.value);
        }
      }

      // Also go through the form's native elements.
      for (var el, i = 0; el = this.elements[i], i < this.elements.length; i++) {
        // If this native element is inside a custom element that has already
        // registered to this form, skip it.
        if (this._isChildOfRegisteredParent(el) || !this._useValue(el)) {
          continue;
        }

        // A <select multiple> has an array of values.