public function unicode($subject) : bool
    {
        if ($subject === null) {
            return false;
        }
        $v = '' . $subject;
        return $v === '' ? true :
            // The PHP regex u modifier forces the whole subject to be evaluated
            // as UTF-8. And if any byte sequence isn't valid UTF-8 preg_match()
            // will return zero for no-match.
            // The s modifier makes dot match newline; without it a string consisting
            // of a newline solely would result in a false negative.
            !!preg_match('/./us', $v);
    }