public static function getBOM(string $which)
    {
        $cname = self::class . '::' . strtoupper($which) . '_BOM';
        if (!defined($cname))
            return null;

        $bytes = constant($cname);
        $bom = '';
        foreach ($bytes as $ord)
            $bom .= chr($ord);
        return $bom;
    }