Naming convention for included make files?

Hi,

I understand that `Makefile` is the conventional name for a root make file, but is there a naming convention for files included using the `include` directive?

From examples in the manual I'd guess that it's `foo.mk` (all lower-case, .mk filename extension).

Alternative suggestions that I've received are `makefile_foo.mk` or `MakefileFoo.mk` (which seem redundant to me) or `Makefile.foo` (which works but seems like a poor idea to me because `foo` could appear to be the file type). The argument for naming them all `Makefile*` is that they'll sort next to each other in file listings.

Thanks