ircg_register_format_messages() を使用することで、 IRC 出力の見た目やクライアント側でどのスクリプトを起動させるかなどを カスタマイズすることが可能です。
Plain channel message
Private message received
Private message sent
Some user leaves channel
Some user enters channel
Some user was kicked from the channel
Topic has been changed
Error
Fatal error
Join list end(?)
Self part(?)
Some user changes his nick
Some user quits his connection
Mass join begin
Mass join element
Mass join end
Whois user
Whois server
Whois idle
Whois channel
Whois end
Voice status change on user
Operator status change on user
Banlist
Banlist end
%f - from
%t - to
%c - channel
%r - plain message
%m - encoded message
%j - js encoded message
1 - mod encode
2 - nickname decode
ircg_lookup_format_messages() も参照ください。