I've just been implementing a bunch of URL-related utility functions in Go. Decided the most pragmatic solution of handling IPv6 addresses in URL hosts is to outright reject zone identifiers because of the ambiguity in how to parse / serialize them, and the inconsistent ways others have done it (or most of the time, not done it).

RFC 3986 says "This syntax does not support IPv6 scoped addressing zone identifiers." Makes sense because '%' is a reserved character for percent encoding (hence the %25 that Go's net/url expects).

The URL Standard explicitly states "Support for <zone_id> is intentionally omitted."