public static function getVisibilityIndex($url = false)
    {
        $url     = parent::getUrl($url);
        $domain  = Helper\Url::parseHost($url);
        $dataUrl = sprintf(Config\Services::SISTRIX_VI_URL, urlencode($domain));

        $html = static::_getPage($dataUrl);
        @preg_match_all('#<h3>(.*?)<\/h3>#si', $html, $matches);

        return isset($matches[1][0]) ? $matches[1][0] : parent::noDataDefaultValue();
    }