[NNTP] Extension snapshots 2

[Clive D.W. Feather]

Russ Allbery said:
> I do agree that the MODE_READER capability
> MUST NOT be advertised (since that invites clients to use it),

Oh hell, I overlooked that. I need to change some of the pre-6 wording.

3.4.2 now says:

   A mode-switching server has three modes:
   o Initial mode, after the initial connection:
      * it MUST advertise the MODE-READER capability;
      * it MUST advertise the IHAVE capability;
      * it MUST advertise the READER capability with the -MODE-READER
        modifier;
      * it MAY advertise other capabilities with the -MODE-READER modifier;
        if these have other modifiers as well, -MODE-READER should be first.
   o Reading mode, after a successful MODE READER command:
      * it MUST advertise the READER capability;
      * it MAY advertise the IHAVE capability;
      * it SHOULD advertise the MODE-READER capability with the -- modifier;
      * it SHOULD advertise, without the -MODE-READER modifier, any other
        capabilities it was advertising with that modifier.
   o Transit mode, after any command except CAPABILITIES or a successful
     MODE READER command:  
      * it MUST advertise the IHAVE capability;
      * it MAY advertise the MODE-READER capability; there are
        circumstances where it SHOULD NOT do so.

and MODE READER now has added:

    The server MAY cease to advertise the MODE-READER capability once
    the client is no longer permitted to use the command, and SHOULD do
    so if the command would have unexpected effects.

I can easily be convinced to change the last two SHOULDs to MUST.

-- 
Clive D.W. Feather  | Work:  <clive at demon.net>   | Tel:    +44 20 8495 6138
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