DNS64: recognize ipv4only.arpa (RFC 8880)
Forwarding or iterative recursive resolvers that have been explicitly configured to perform DNS64 address synthesis in support of a companion NAT64 gateway (i.e., "DNS64 recursive resolvers") MUST recognize 'ipv4only.arpa' as special.
but there might be more requirements to follow in the RFC 8880.
EDIT: to be clear, resolvers not configured to do DNS64 synthesis SHOULD NOT recognize these names as special.