Credential Format Identifiers: no collision guidance, no registry

This document recommends collision-resistant naming in four places, for four different value spaces:

It is RECOMMENDED to use collision-resistant names for type values.

Ecosystems SHOULD use collision-resistant identifiers.

It is RECOMMENDED to use collision-resistant scopes values.

Other specifications can define further Client Identifier Prefixes. It is RECOMMENDED to use collision-resistant names for such values.

Those are transaction data types, verifier_info formats, scope values and Client Identifier Prefixes. Credential Format Identifiers get no equivalent, and searching for any other collision-related guidance I found none.

They are also the one of those spaces where a collision has already happened. SD-JWT VC records it in its own note: the identifier "was changed to dc+sd-jwt to avoid conflict with the vc media type name registered by the W3C's Verifiable Credentials Data Model draft". The cost is still being carried, since that note asks implementations to accept both names for a transitional period.

The extension model for these identifiers is also stated two ways. Appendix B is presented as the definitive list, "Valid Credential Format Identifier values are defined in Appendix B", while Sections 10.1 and 11.1 both say "Deployments can extend the formats supported, provided Issuers, Holders and Verifiers all understand the new format", and Appendix B adds that "other specifications or deployments can define their own set of Credential Format specific parameters". I could not find a registry or a naming convention for those extensions in this document.

Should Credential Format Identifiers carry the same collision-resistance recommendation as the other four spaces, and is the value space intended to be open or closed?

Read the collision-resistance guidance quoted in the issue alongside Sections 10.1 and 11.1 and Appendix B. Determine whether Credential Format Identifiers should have collision guidance and whether their value space is open or closed, then update the relevant specification text and ensure the SD-JWT VC transition note remains consistent.