This is activated whenever you receive a dmsg from someone. The parameters for the action are as follows:
$0 nickname of person who sent the dmsg
$1- The message
Warning: As dmsg is outside the IRC protocol, it allows you to send a dmsg from an on/dcc_chat. This has the potential to create loops. If you intend to send a dmsg from DCC_CHAT you are responsible for ensuring that it will not create a loop.