1. Every response to a request on a reference MUST include Ref-Type
2. Every response to a request on a direct reference MUST include Ref-Target
3. Every (successful) response to a GET or HEAD request on a redirect reference MUST include Ref-Type, Ref-Target, and Ref-Integrity
1. So that a referencing-aware client can tell whether it was operating on a reference, and whether the operation was (by default) applied to the reference or to its target. This can be helpful especially in case of a 3xx or 4xx response, or to let the client know that it must resolve a redirect reference in order to do anything useful.
2. Exceptions: if the reference was created with Hide-Target, or if the current request included Re-Direct.
So that the client can tell what resource was affected by its request.
3. Follows the general rule for GET and HEAD, that responses MUST include all entity headers for the resource