I am the designated ARTART reviewer for this draft.

This document is well written and appears to be ready for publication as an Informational RFC.

Minor issue: I would prefer if the New Text in Section 3 used normative terms (probably MAY in most cases) for consistency with IETF style. However, the way it is written is consistent with the wording in Section 5.7 of RFC7315, so this may be a reason to stick with the current "can" wording. Presumably none of the named header fields are mandatory in any of the named requests and responses; if some are, more precise normative terminology is needed.