ments.
      var validatable;
      for (var el, i = 0; el = this._customElements[i], i < this._customElements.length; i++) {
        if (el.required && !el.disabled) {
          validatable = /** @type {{validate: (function() : boolean)}} */ (el);
          // Some elements may not have correctly defined a validate method.
          if (validatable.validate)
            valid = !!validatable.validate() && valid;
        }
      }

      // Validate the form's native elements.
      for (var el, i = 0; el =