on [<modes>]disconnect [<serial#>] [-|^]<match> { <action> }

This hook is triggered whenever you are

1) [[kill]]ed by an operator, 
2) Run a command that sends data to the server, in a window that is not connected to a server
3) You [[disconnect]] from your last server.

and perhaps for other reasons in the future.

If you don't suppress this event, the client will format and display a message to your screen.

To customize the disconnection message:

 on ^disconnect * (server) {
    xecho -b Disconnected from $server at $Z
 }