Is header order significant? [was: Concrete format for signed responses]

On Wed, Dec 6, 2017 at 10:42 AM Mike Bishop <mbishop@evequefou.be> wrote:

> ... The advantage of your current scheme is that you can preserve the
> original order of the headers in the signature, meaning a client could
> detect changes / reconstruct them.  I’m not sure how critical that is, but
> this is the right list to give feedback on the semantic content of header
> ordering….
>
>
Pulling this out to its own thread since it's more general than the
signed-exchange proposal:

Is the order of HTTP headers semantically significant? Should future
proposals be careful to preserve header order, or is it ok to do things
like sort headers while processing them?

Thanks,
Jeffrey