What parseCidrv4 returns and what stringifyCidrv4 accepts: a Cidrv4 in the dialect it was written in, plus the zone ID if the notation had one (fe80::%ether1/64 has one; RouterOS emits that form for connected routes). Assignable to Cidrv4, so a parse result goes straight into every cidrv4* operation; none of them reads the zone.