public static function check_webkit_android_version($version = null) {
        // WebKit browser on Android.
        $useragent = self::get_user_agent_string();
        if ($useragent === false) {
            return false;
        }
        if (strpos($useragent, 'Android') === false) {
            return false;
        }
        if (empty($version)) {
            return true; // No version specified.
        }
        if (preg_match("/AppleWebKit\/([0-9]+)/i", $useragent, $match)) {
            if (version_compare($match[1], $version) >= 0) {
                return true;
            }
        }
        return false;
    }