I like the hierarchical naming.

C somehow lacks namespaces, but the '_' char does it well!

It is an idiom well-adopted by the community for library namespaces, so that the integrate well with the end project.

Some project end up using namespaces for splitting different sections of their library.

If you combine the two (let's say, it is a general purpose programing library with multiple sections), you get a 2-fold library namespace.