Well, I just figured out how to do what I want, but it took me a while. I need a filter to INCLUDE files, but Yummy only gives you a way to EXCLUDE files. OK so I finally figured out that to INCLUDE files that begin with S (source) OR M (macros), you need to EXCLUDE files that do not begin with S AND do not begin with M.
Good thing I remember DeMorgan's law. The interface could be a bit more intuitive.
Cheers,
Richard