ietf-nntp LIST EXTENSION caching, latest wording

[Clive D.W. Feather]

Rob Siemborski said:
>> In 5.3.2, one paragraph:
>>
>>    While some extensions are likely to be always available or never
>>    available, others will "appear" and "disappear" depending on other
>>    changes. An NNTP client may cache the results of this command, but
>>    MUST NOT rely on any cached results - whether from earlier in this
>>    session or from a previous session - remaining correct, MUST cope
> 
> Note that what you're saying here is that I have to issue LIST EXTENSIONS
> right before I execute every command -- and even that isn't really good
> enough, since the server can randomly change LIST EXTENSIONS after every
> time you issue it (a bogus server, but this is what this requirement is
> doing to the client)

Oops. True (a "weirdnix", it's called elsewhere).

>   others will appear and dissapear depending on state changes within
> the session.

I already had "server state or external events", but even better is "server
state changes within the session or external events between sessions".

> An NNTP client MAY cache the results of this command, but
> MUST NOT rely on any cached results - from previous sessions or across
> session state changes that are documented to potentially invalidate
> the LIST EXTENSIONS response - remaining correct.

Um, that requires a consequential change in section 8, but one I agree
with:

    * a specific statement about the circumstances when use of this
      extension can alter the output from LIST EXTENSIONS;

In fact, looking at it, I'd rather leave the "MUST NOT rely" text alone,
but I'll make the change in 8.

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