public static function daysList($days)
    {
        foreach($days as $day)
        {
            // if it isn't negative, it's positive
            $day = ltrim($day, "+");
            $day = trim($day);

            $ordwk = 1;
            $weekday = false;

            if (strlen($day) === 2)
            {
                $weekday = $day;
            }
            else
            {
                list($ordwk, $weekday) = sscanf($day, "%d%s");
            }

            if (!self::weekDay($weekday) || !self::ordWk(abs($ordwk)))
            {
                return false;
            }
        }

        return true;
    }