file vs sub file (Part 3, Draft 11)

Dear all,

P D1.2.2 uses the term "sub file" for the first time.

What is this "sub file"?

What is the relationship between this "sub file" and the "file"
mentioned in P D1.2?

It seems the terms "file" and "sub file" may be used interchangeable for
the same thing ...

- Alex.