protected function searchSubmitHandler(): ?string
  {
    switch ($this->attributes['method'])
    {
      case 'post':
        $values = &$_POST;
        break;

      case 'get':
        $values = &$_GET;
        break;

      default:
        throw new FallenException('method', $this->attributes['method']);
    }

    return $this->fieldSets->searchSubmitHandler($values);
  }