When\When::getFirstWeekStartDate PHP Method

    public static function getFirstWeekStartDate($startDate, $wkst)
    {
        $wkst = self::abbrevToDayName($wkst);
        $startWeekDay = clone $startDate;
        // Get first $wkst before or equal to $startDate
        $startWeekDay->modify("next " . $wkst);
        $startWeekDay->modify("last " . $wkst);
        return $startWeekDay;
    }