I think that the other answers you got are definitely more on-topic wrt your question, but I'd like to mention that while I've never used formats myself nor did I think they were much used any more I've heard that there's an OO module by Damian Conway to use instead, that incidentally in the (IMHO authoritative) opinion of who supplied this piece of info provides additional functionality. Now, chances are that this may give you what you need straight out of the box...