Parametr $sequence u getInsertId v MySQL driveru

K čemu je parametr $sequence u metody getInsertedId v MySQL driveru protože z tohohle moc moudrý nejsem:

/**
 * Retrieves the ID generated for an AUTO_INCREMENT column by the previous INSERT query.
 * @return int|FALSE int on success or FALSE on failure
 */
public function getInsertId($sequence)
{
    return mysql_insert_id($this->connection);
}