What parseCidrv6 returns and what stringifyCidrv6 accepts: a Cidrv6 in the dialect it was written in, plus the zone ID if the notation had one (fe80::%ether1/64, the form RouterOS and netstat -rn emit for link-local routes). Assignable to Cidrv6, so a parse result goes straight into every cidrv6* operation; none of them reads the zone.