Note: This scheme has been documented by an IETF working group
and is mentioned in an IETF Standard specification.  However,
as it describes a locally scoped, limited-purpose form of
identification, it does not fully meet the requirements for
permanent registration.

As long as this specification (RFC 9393, or any 
successors that describe this scheme) is a current IETF 
specification, this scheme should be considered to be "in use" and 
not considered for removal from the registry.