CoAP: Non-traditional response forms

In CoAP as defined by RFC 7252, responses are always unicast back to a client that posed a request. The present memo describes two forms of responses that go beyond that model. The design spaces for the new CoAP Options proposed to represent these responses are now sufficiently understood that they can be developed to standards-track specifications, either in this document or by transferring the specification for an Option to a document that that Option closely works with.