Commonly-used relation types with a clear meaning that are shared
across applications can be registered as tokens for convenience and
to promote reuse. For example, "self" and "alternate" are registered
relation types, because they are broadly useful.
The registry also outlines the process which involves a dedicated expert and public comment period:
6.2. Link Relation Type Registry
This specification establishes the Link Relation Type Registry, and
updates Atom [RFC4287] to refer to it in place of the "Registry of
Link Relations".
The requirements for registered relation types are described in
Section 4.1.
Relation types are registered on the advice of a Designated Expert
(appointed by the IESG or their delegate), with a Specification
Required (using terminology from [RFC5226]).
Registration requests consist of the completed registration template
below, typically published in an RFC or Open Standard (in the sense
described by [RFC2026], Section 7). However, to allow for the
allocation of values prior to publication, the Designated Expert may
approve registration once they are satisfied that an RFC (or other
Open Standard) will be published.
The registration template is:
o Relation Name:
o Description:
o Reference:
o Notes: [optional]
Upon receiving a registration request (usually via IANA), the
Designated Expert should request review and comment from the
apps-discuss@xxxxxxxx mailing list (or a successor designated by the
APPS Area Directors). Before a period of 30 days has passed, the
Designated Expert will either approve or deny the registration
request, communicating this decision both to the review list and to
IANA. Denials should include an explanation and, if applicable,
suggestions as to how to make the request successful.
Ironically the apps-discuss list wasn't included so I am adding them now. One nitpick about the process is that it seems a request can be denied with a suggestion for another relation (for example we might prefer to use something like "push" or "notif[y|ier|ication|ications" rather than "hub" for this one) but then that would require restarting the process where it should proceed to registration immediately if the change is accepted by the applicant.
I also question the relevance of the "reference" field in the registry as this links relations to implementations which I think we agree is a bad thing - the registry should capture all the necessary semantics without reliance on external references. It may be interesting to list zero or more implementations of the relation (that is, make the "reference" field optional as well and allow others to add themselves to it), however I'm not sure the maintenance load is worth the effort.