protected static function digit_to_char($digit) {
		if ($digit < 0 || $digit > 35) {
			throw new Requests_Exception(sprintf('Invalid digit %d', $digit), 'idna.invalid_digit', $digit);
		}
		$digits = 'abcdefghijklmnopqrstuvwxyz0123456789';
		return $digits[$digit];
	}