private static function getDays(int $maxDays = 31): array
    {
        $days = [-1 => static::getConstant('TXT_DATETIME_DD', 'TXT_DATETIME_DD')];
        for ($i = 1; $i <= $maxDays; $i++) {
            $days[$i] = \sprintf('%02s', $i);
        }
        return $days;
    }