Project generator: additional sources

I have some questions regarding the additional sources feature of the pg.
the project generator (nightly) has an option to add additional sources which will be added to the generated IDE project.

  • does it also get added to the make files?
  • does it get stored somewhere or do I have to re-add them every time I regenerate the project?
    I am wondering how this could be best added to the package manager tool I am working on and how they differ from addons (or local addons outside of the project directory).