Proposed text for erratum on PRIORITY in RFC 7540

[Martin Thomson <[e-mail]>]

I figure that I might try to nut this out here before opening an
erratum.  It's not clear from the thread that we all understand this.

I think that suggesting two additions is the right thing here.  It's
an erratum, so we don't have to do a proper edit, we can leave that
for some future revision of the spec to get precisely right.

In Section 5.3 (Stream Priority) a new paragraph:

> The information that an endpoint maintains for stream priority is separate from other state. Importantly, this includes stream states (Section 5.1).  A stream in any state can have its priority changed with a PRIORITY frame. The state of a stream is not changed as a result of changing its priority.  The number of streams for which state is remembered is at the discretion of an endpoint, see Section 5.3.4 for details.

In Section 6.4 (PRIORITY) a new sentence at the end of the first paragraph:

> Sending or receiving a PRIORITY frame does not affect the state of the identified stream (Section 5.1), only its priority is altered.

I think that we only really need one piece of clarification (the
second would be enough), but it doesn't hurt to make it clear in both
places that one might go to learn this.