Extbans are all provided by extensions, some may not be present on this
server.

EXTBAN - DESCRIPTION
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     $o         Oper extban. Affects all operators.
     $z         SSL extban. Affects all users connected via SSL.
     $a[:mask]  Account extban. Affects anyone with an account that
                matches. If the mask is omitted, it affects everyone
                who is logged into services.
     $j:mask    Banned from another channel extban. Affects anyone who
                is banned from the specified channel.
     $c:mask    Other channel extban. Affects anyone who is on the 
                specified channel.
     $x:mask    Extended extban. Matches a user's entire n!u@h gecos.
     $r:mask    GECOS extban. Affects anyone with the realname/gecos
                specified.
     $s:mask    Server extban. Affects anyone on the specified server.