The on CHAT and on SERV events trigger when a message is sent to a dcc chat or dcc fserve window.
Format: on <level>:CHAT:<matchtext>:<commands>
Example: on 1:CHAT:*help*:/msg $nick what is the problem?
For an explanation of matchtext see the on TEXT event.
on 1:CHAT:boo!:/msg =$nick Boo back at ya!
This triggers when someone in a dcc chat window says boo! The equal sign in =$nick is required to send the reply as a dcc chat message. If no equal sign is used, the message is sent as a private irc server message.
on 1:SERV:bye:/msg =$nick Thanks for using my fileserver, bye!
This triggers when a user in a dcc fileserver session says the word bye to quit the fileserver. You can also refer to the $cd identifier to reference the current directory a fileserve is in.
Note: These events react to all users level 1 and above because of the way dcc chat works.