Sure. HTTP/1.1 isn't the only network protocol, though, IETF standardization or otherwise.

For SMTP (which this subthread started with):

   In addition, the appearance of "bare" "CR" or "LF" characters in text
   (i.e., either without the other) has a long history of causing
   problems in mail implementations and applications that use the mail
   system as a tool.  SMTP client implementations MUST NOT transmit
   these characters except when they are intended as line terminators
   and then MUST, as indicated above, transmit them only as a <CRLF>
   sequence.

https://datatracker.ietf.org/doc/html/rfc5321#section-2.3.8

Can you provide a citation for this? I’ve read older RFCs that "recommend" recipients allow single LFs to terminate headers for robustness. I’ve also read newer RFCs that weaken that recommendation and merely say the recipient "MAY" allow single LFs. I’ve never noticed an HTTP RFC say you can send headers without the full CRLF sequence, but maybe I missed something.

https://datatracker.ietf.org/doc/html/rfc2616#section-19.3 https://datatracker.ietf.org/doc/html/rfc9112#section-2.2

Ah, this is a subthread about HTTP specifically - didn't notice. Explains why you focused on the IETF too. Nevertheless, my points I believe still all stand.

As for HTTP or any other protocols' definitions go, I'd rather not join in on that back and forth. I'd imagine it's well defined what's expected. Skim reading RFC-2616 now certainly suggests so.

none of this is as clear as anyone wants it to be. if standards _could_ be completely formally described, it would be an entirely different world. I did quite a bit of work implementing draft standards in the IETF, and and the end of the day the standard is the best we can make it, but for non-trivial things good luck actually implementing it without something to test against or a reference implementation.

thats the context in which Postel's law make absolute sense. not that you should forgo any sanity checking, or attempt to interpret garbage or make up frame boundaries. but when there is a potential ambiguity, and you can safely tolerate it, then its really helpful for you to do so.