public function setStartDay($startDay)
    {
        $startDay = (int) $startDay;

        if ($startDay < 1 || $startDay > 7) {
            throw new OutOfRangeException(
                "'$startDay' is an invalid value for \$startDay in '"
                . __METHOD__
            );
        }

        $this->startDay = $startDay;

        return $this;
    }