Extbans are split into two types: matching extbans, which match on
users in different ways, and acting extbans, which restrict users
in different ways to a standard ban.

To use an extban, simply set +b/e/I <ban> with it as the ban,
instead of a normal nick!user@host mask, to ban or exempt matching
users.

Matching extbans:

 $a:<account>   Matches users logged into a matching account.

 $c:<channel>   Matches users that are on the given channel. An additional
                prefix of either @, %, or + can be specified to test for
                certain channel privileges.

 $o:<class>     Matches IRC operators that have joined a class
                matching the mask.

 $r:<realname>  Matches users with a matching realname.

 $s:<server>    Matches users that are connected to a server matching the mask.

 $u:<modes>     Matches users having the specified user modes set or not set.

 $z:<certfp>    Matches users having the given TLS certificate fingerprint.

Acting extbans:

 $j:<banmask>   Prevents matching users from joining the channel.

 $m:<banmask>   Blocks messages from matching users. Users with voice
                or above are not affected.

 $n:<banmask>   Prevents matching users from changing their nicks. Users with
                voice or above are not affected.

A ban given to an acting extban may either be a nick!user@host mask,
matched against users as a normal ban, or a matching extban.
