p2: Considerations for new headers

[Mark Nottingham <[e-mail]>]

We should consider adding the following to the laundry list of considerations in p2 8.3.1:

* Whether the field should be stored by origin servers that understand it upon a PUT request.

Furthermore, I think we should change:

* How the header field might interact with caching (see [Part6]).

to:

* When the header is used in requests and affects response selection [ref], it is good practice to advise listing that header in the Vary response header [ref].

Finally, we should add (near the top of the section):

"""
New header fields cannot change the semantics of a message in an incompatible fashion. That is, it is not possible to require recipients to understand a header field through its mere presence. However, new methods and status codes can require the presence of headers in their definitions, in the scope of the message they occur within. 
"""

Make sense?


--
Mark Nottingham   http://www.mnot.net/