In BRL's MUVES project, we used a 2-character prefix indicating category. E.g., all the external identifiers for our fancy memory allocator began with "Mm", where Mm.h documented the interface for the Mm package only.

To minimize the external identifiers, one could make just the name of a container structure the sole entry access handle, with structure members pointing to the functions. Then use it like:

  #include <Mm.h>
  if ((new = Mm.allo(size)) == NULL)
    Er.abort("out of memory");