public function firstImageUrl(string $markdown): string
    {
        $regex      = '/(?<=^|[\s;,])\!\[[^\v[\]]*\]\((?<url>https?\:\/\/[^\s()]+?\.(?:png|jpeg|jpg|gif))\)(?=$|[\s.!?;,])/ui';
        return $url = $markdown && preg_match($regex, $markdown, $_m) ? $_m['url'] : '';
    }