public static function toProtobuf($object, $filter = NULL)
	{
		$output = '';

		if (isset($object->start) && ($filter === null || isset($filter['start']))) {
			$output .= "\x08";
			$output .= Binary::encodeVarint($object->start);
		}

		if (isset($object->end) && ($filter === null || isset($filter['end']))) {
			$output .= "\x10";
			$output .= Binary::encodeVarint($object->end);
		}

		return $output;
	}