public function run()
    {
        if (!empty($this->_fields)) {
            throw new InvalidCallException('Each beginField() should have a matching endField() call.');
        }

        $content = ob_get_clean();
        $html = Html::beginForm($this->action, $this->method, $this->options);
        $html .= $content;
        $html .= Html::endForm();

        return $html;
    }