======Synopsis:======
[[on]] [<modes>]public_other [<serial#>] [-|^]<match> { <action> }

======Description:======
This hook is triggered whenever the client observes a message sent to
any channel it is on that isn't its current channel, from someone else
on that channel.

======Parameters:======
|$0 |nickname sending message|
|$1 |channel sent to|
|$2- |text of message|