Regarding byte ranges, an empty (zero-length) representation is unsatisfiable according to section 2.1, but not unsatisfiable according to section 4.4 if the first-byte-pos is zero.

I would like to see an update to the RFC which explicitly resolve this self-contradiction in whatever way seems appropriate. The following is one suggestion, but there may be others:

I would like to suggest explicitly specifying that an empty 200 response should be returned in this case. It is the simplest solution to the current self-contradiction in the RFC, since it is a valid response anyway (if the server chooses to ignore the Range header), clients already handle it properly, it provides all necessary information about the representation to the client, and stating it explicitly can prevent subtle edge-case pitfalls in both the RFC and its implementations (as opposed to more intricate solutions).

Perhaps the following can be added at the end of section 3.1:
"If all of the preconditions are true and the target representation
length is zero, the server SHOULD send a 200 (OK) response."

(someone in the discussion preferred this to be a MUST, but the SHOULD might be more in line with the previous sections and backward-compatibility if some implementations resolved this in some other way.)

I raised this in the mailing list a while back, and it got some discussion and support but did not get officially resolved. More recently I reported it as errata but it was rejected as not being an erratum and redirected here (I apologize - didn't realize issues moved to github, and still not sure what the distinction is :-) ), so here it is, raised again.

All suggestions and feedback are welcome.