[Kamailio-Users] what does the following line mean

[Rajesh]

Dear Experts,
                            Iam configuring IMC and i would like to know 
what does the following line mean.

  xdbg("script: message from [$fu]  chatroom000 [$ru] msg [$rb]\n");


.I get error in this line when i start kamailio. what does $fu ,$ru , 
$rb mean.


Thanks