Original text:
header field includes information about the selected representation's complete length. <del> A sender that generates a 206 response with an </del>  header field SHOULD NOT generate other representation header fields beyond those required, because the client already has a prior

Reviewer comments:
For
[x] (7.6.3) Via "If a port is not provided, a recipient MAY interpret that as meaning it was received on the default TCP port, if any, for the received-protocol." So if received-protocol is "3", it's a UDP port. If received-protocol is "1" or "1.1", is the default port 80 or 443? IIUC the scheme isn't included to determine this. Editors: URL [x] (7.7) Message Transformations "A proxy that transforms the content of a 200 (OK) response can inform downstream recipients that a transformation has been applied by changing the response status code to 203 (Non-Authoritative Information)" Why not an normative word, instead of "can"? Editors: URL [x] (12.5.3) Is it correct that "identity" and having no field value for Accept-Encoding are synonymous? Editors: URL [x] "Servers that fail a request due to an unsupported content coding ought to respond with a 415 (Unsupported Media Type) status" Why not s/ought to/SHOULD ? Editors: URL [x] (14.3) Why can only origin servers send "Accept-Ranges: bytes"? Why not intermediaries? Editors: URL [x] (15.3.7) "A sender that generates a 206 response with an If-Range header field"... (13.1.5) leads me to believe that only clients can send If-Range. So how can there be a response with If-Range? Editors: URL [x] (15.3.7.2) The last instance of THISSTRINGSEPARATES has a trailing '--'. If this is intentional, it ought to be explained. Editors: URL [x] (16.3.1) says field names SHOULD begin with a letter, but (16.3.2.1) says they SHOULD begin with "an alphanumeric character". More broadly, the "Field name:" description in (16.3.1) should probably refer to (16.3.2.1) unless I'm misunderstanding the scope of these sections. Editors: URL [x] (17.13) s/TCP behavior/TCP or QUIC behavior Editors: URL [x] (B) It would be good to mention here that accept-ext has been removed in (12.5.1), and accept-charset is deprecated in (12.5.2), if that is new to this spec. Editors: see URL and URL
Because it isn't required, nor is it widely implemented (if at all). We try not to make requirements that we know won't be honoured.
Because the header is information about the capabilities of the origin server, not other members of the request chain. Intermediaries can change (e.g., with proxy configuration). Note that a gateway (e.g., a CDN) is effectively acting as an origin server, so it can do this. The language in this section needs to be tweaked, however; there are a few instances of 'server' that should be 'origin server'.
field"... (13.1.5) leads me to believe that only clients can send If-Range. So how can there be a response with If-Range? It looks like the phrase 'to a request' was dropped somewhere between and now.
this is intentional, it ought to be explained. This is how multipart works; see . I don't think there's value in re-specifying it here.
As per the spec: ...
Because we avoid making existing servers that predate this spec non-compliant (unless there's a very good reason, such as security)

Revised text:
header field includes information about the selected representation's complete length.  <ins> A sender that generates a 206 response to a request with an </ins> header field SHOULD NOT generate other representation header fields beyond those required, because the client already has a prior