on/about a stream, frame ordering

I feel like we've discussed this in the interim meetings, but I don't see
any language about this in the spec. I see many references to "on a
stream", but I can't find anything "about a stream". Is this language we
plan to formalize in the spec?

Also, we've discussed what frames are allowed to be reordered by
intermediaries, based on whether they are on/about a stream. I don't think
I've seen anything about this in the spec. Do we have plans to discuss this
in the spec?

Cheers.