-spec is_bogon(binary() | string()) -> boolean().

Whether an address is private, loopback, link-local, documentation, multicast or otherwise not routable on the public internet, including the IPv6 equivalents and the 6to4 and Teredo ranges that wrap them.

Anything that is not a well-formed address is false: the API decides what counts as an address, and answering true here would swallow the 400 that tells the caller their input was wrong.

-spec unmapped(binary()) -> binary().

The IPv4 address an IPv4-mapped IPv6 address (::ffff:a.b.c.d, in any spelling) carries, dotted, and any other address as given.

A server listening on :: sees every IPv4 visitor in that form, which read whole is inside ::ffff:0:0/96, so judging it whole would answer every such visitor locally as a bogon. ::a.b.c.d is IPv4-compatible rather than mapped, and stays IPv6.