[Brian]

Structurally, I don't believe there's any difference between the three. It just helps differentiate the different purposes they're intended for.

I know opening/editing multiple .ofocus and -backup files is something the app design takes into account and supports. I'm not aware of any negative effects caused by having multiple -archive files open or editing them, but I can't be sure that we took that possibility into account when designing the app.

I'd stick with one of the former two types of file, but only because I'm paranoid like that. :-)