It looks like "request" and "response" are defined inhttps://httpwg.org/http-core/draft-ietf-httpbis-semantics-latest.html#operation as kinds of "messages", and then "messages" are defined in the same section by reference tohttps://httpwg.org/http-core/draft-ietf-httpbis-messaging-latest.html#http.message ... which only applies to HTTP/1.1. Ithink these are intended to be version-independent concepts, so they need a version-independent definition.