UDP broadcast and NAT


It's my understanding that UDP broadcast messages are never
transmitted across NAT. Can someone tell me if that is correct?
Or, if it is possible, under what circumstances.

I am considering putting together some code which broadcasts
messages. I'm trying to avoid broadcasting outside of the local
network; I don't want to generate unneeded traffic.

Sorry for this simple-minded question. Any light you can shed on
this topic is much appreciated.

Robert Dodier