Registered names and extension relations
04A short registered name and an absolute extension URI can both identify link semantics; neither is a command to fetch documentation.
rel="next https://rels.example/picnic" describes two links between the same context and target. It is one parameter containing a space-separated list, not a duplicate rel.
Source for this drawing: RFC 8288 · Read RFC section 2.1 ↗
New to this? Start hereA quick picture + helpful background
A message needs an address.
Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
- Relation type
- The semantics of the connection between context and target.
- Extension relation
- An application-defined relation identified by an absolute URI in a Link field.
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
Registered relation names follow the reg-rel-type syntax and MUST be compared character by character case-insensitively. The registry uses Specification Required review and stable, freely available specifications.
- Registered relation names follow the reg-rel-type syntax and MUST be compared character by character case-insensitively. The registry uses Specification Required review and stable, freely available specifications.
- An extension relation in an HTTP Link field is REQUIRED to be an absolute URI. Extension relation identifiers MUST be compared as case-insensitive strings; all-lowercase URIs SHOULD be used.
- Clients SHOULD NOT automatically access an extension relation URI just because it identifies a relation. Its identifier and the link target have different roles.
- Relation types SHOULD NOT infer extra meaning from presence/absence of other types or cardinality; the alternate/stylesheet combination is a historical HTML exception. The reverse-direction rev parameter is deprecated.
Generate lowercase registered names. Case-insensitive comparison is the specified comparison behavior, not a reason to broaden the lowercase generation grammar. The fictional extension https://rels.example/picnic is assumed controlled by its defining application, not registered by this guide. Quote relation values when token syntax cannot represent their characters. Do not prepend a made-up registry base to a registered name and assume equivalent semantics.
Read the RFC section ↗