Original text:
9.2. <del> The permanent message header field registry (see RFC3864) needs to be updated with the following registration: </del>  Set-Cookie

Reviewer comments:
Adds suggestions for how servers could fulfill the requirement Adds suggestion that servers be mindful of the number and size of the cookies they set to avoid hitting their own header length limits. Also mention that UA should consider splitting longer fields.
If that's the case, I'd recommend punting on getting this in 6265bis - which has had a goal of documenting reality.
It is not unusual for servers to reject HTTP requests that contain individual headers longer than a certain limit. If a client sends a header longer than around 8-9K bytes, the risk is quite large that it will get a 40x response back which effectively blocks the client from continuing what it is set out to do. Because of the rather complicated results of such a "too long" cookie header, I think it could be worth mentioning this in the spec. For newcomers in cookie land, this is perhaps not completely obvious. The spec currently mentions size-limits per cookie, but a server can easily send a few large cookies and have the combined size of them outgrow 8K. I would perhaps suggest wording that says a client SHOULD keep its lines shorter than NNN bytes and servers SHOULD accept cookie lines up to at least NNN bytes. (in curl we have the limit set to 8190 bytes) HTTP related specs rarely speak of this kind of size limits, but I know my implementation could have avoided some issues if this real-world limit had been mentioned.
Seems like a worthwhile warning to me.
RFC 6265 had a requirement that a client MUST generate a single cookie header. HTTP/2 and HTTP/3 allow "cookie crumbling" that permits multiple Cookie headers. 6265bis says in URL What is tolerance really? Why are we stating MUST requirement that are immediately invalidated by two of the versions of HTTP in wide usage? Section 5 is huge, what requirement is the text in section 4.2 forward referencing to? I think there's some room for improvement in this area. An HTTP/2 or HTTP/3 is being instructed as a MUST requirement in the relevant RFCs to combine multiple cookie headers into one e.g. URL but if the server MUST be tolerant to multiple Cookies, maybe we can relax the HTTP/2 or HTTP/3 requirements?
This was the output of the discussion in URL
Thanks Mike, I missed that discussion first time around. My question comes about because of some HTTP/2 code I looked at that simply implements HTTP/2 and so combines the multiple fields back into one. But as NAME and NAME alluded to their comments on , the splitting could be done for some reason thst isn't purely about H2 or H3 compression optimization. It seems there are actually use cases where keeping the split is useful, and not just in a private deployment. Of course relaxing things more might have unintended consequences. I find the current text too terse to be useful. This is a cookie spec, it seems like the right place to ba adding commentary about how to handle cookies across various version and conversions. Especially some anecdotal examples about why some clients actually do it.
Mentioning why a server should be tolerant, and what shape that could take, seems reasonable to me. Especially given how nicely it dovetails with . What forward reference are you referring to? ?
In that mention, I think it's worth including that re-combining the Cookie lines before passing to the next layer is a form of tolerance from the client's perspective.
Some more text sounds good and I'm happy to review. In Section 4.2.1:
Still LGTM, thanks!

Revised text:
9.2.  <ins> The permanent message header field registry (see HttpFieldNameRegistry) needs to be updated with the following registration: </ins> Set-Cookie