How to reference code in the lib folder for go functions

The documentation in the How to Structure Project page of the functions documentation mentions that shared files can be placed in the lib directory in the root of the functions repository.

The project can also contain a top-level lib directory, where files common to multiple packages can be stored or built. See Build Process for details on the build process and its use of the lib directory.

I take this to mean that shared code can be placed in the lib directory but I haven’t been able to find any documentation for how to do this. I’m specifically looking for examples of how to do this with go functions.