account-notify client capability specification
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Copyright (c) 2010 William Pitcock <nenolod@atheme.org>.

Unlimited redistribution and modification of this document is allowed
provided that the above copyright notice and this permission notice
remains in tact.

The account-notify client capability allows a client to be notified
when another client's accountname changes.  This capability MUST be
referred to as 'account-notify' at capability negotiation time.

When enabled, clients will get the ACCOUNT message to designate the
accountname changes for clients on common channels with them.

The ACCOUNT message is one of the following:

   :nick!user@host ACCOUNT accountname

This message represents that the user identified by nick!user@host has
logged into a new account.  The last parameter is the display name of
that account.

   :nick!user@host ACCOUNT *

This message represents that the user identified by nick!user@host has
logged out of their account.  As the last parameter is an asterisk, this
means that an asterisk is not a valid account name (which it is not in P10
or TS6 or ESVID).

In order to take full advantage of the ACCOUNT message, WHOX must be
supported by the ircd.  In this case, the appropriate strategy to ensuring
you always have the accountname to display is to do the following:

1) Enable the account-notify capability at capability negotiation time during
   the login handshake.

2) When joining a channel, query the channel using WHO and ensure that you
   include the 'a' format token in your WHOX token request.  When you get
   a reply, do appropriate caching.

3) If the extended-join capability is available, enable it at client capability
   negotiation time during the login handshake, and then set the accountname
   based on what is sent in the extended JOIN command.

   Otherwise, if extended-join is unavailable:
   When new users join a channel that your client does not know the accountname
   for yet, do a WHO query against that client, again including the 'a' format
   token in your WHOX token request field.  When you get a reply, do appropriate
   caching.

4) In the event of a netsplit, the client should query the channel again using
   WHO with the 'a' format token in the WHOX request field.

5) When the client receives an ACCOUNT message, update the accountname for the
   client in question in your accountname cache.
