In section 5.4, there are a couple of normative requirements for HTTP/1.1 ("A client MUST send a Host header field in all HTTP/1.1 request messages."; "A client MUST send a Host header field in an HTTP/1.1 request"; "A server MUST respond with a 400 (Bad Request) status code to any HTTP/1.1 request"), and it makes two references to the absolute-form production, which is defined in the Messaging draft (and hence is a dangling reference in Semantics). Those should probably live in Messaging, and the Semantics document should be more general.