It was a requirment in the Blue Book, and I think, the one before that. (Was it the red book?) So, and this from memory, about 2004 or 5 for the Blue Book, and some 7 or 8 years earlier, if I am right about the "red(?) Mbook. Alan MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.