[otrs] dtl how it works??

Hi! I'm trying to understand how de block of dtl works and how dtl work! I'm making some changes in the agent interface,i'm working on AgentTicketQueue.dtl and at some lines it appear something like <!-- dtl:block:QueueNav -->.I'm wondering if what comes below this is the <!-- dtl:block:QueueNav --> or this is a call to a block already defined. So if is like a function where is the body of the function?? Compliments      Ricardo Tavares     (Computer Engenieer) Simplesnet GTI, a net até 6 vezes mais rápida, ao mesmo preço de sempre! http://www.simplesnet.pt/