public static function isLeapYear($year)
	{
		$year = self::digitCheck($year);
		if ($year % 4 != 0)
			return false;

		if ($year % 400 == 0)
			return true;
		// if gregorian calendar (>1582), century not-divisible by 400 is not leap
		elseif ($year > 1582 && $year % 100 == 0 )
			return false;
		return true;
	}