My recollection of our most recent discussions of this draft were that it _might_ make sense to allow configuration of what version(s) of HTTP a server supports, but not a client. Since -17, it appears the opposite has been done: while server configuration remains the same, client configuration now allows enumeration of supported versions. 

Additionally, support is indicated by using separate, version-specific indicators. This is a closed list and does not accommodate future versions of the protocol. Can this be an array of strings instead? That would also allow us to avoid the awkward phrasing in the introduction, which leads readers to believe the set of HTTP versions is closed (counter to BCP56).