I'm sharing https://github.com/pyTooling/Actions/#context here, which is general information about GitHub Actions' Action kinds, particularly Composite Actions and Reusable Workflows. That is the "theory" behind the CI plumbing being used in https://github.com/hdl/containers. At the same time, I'm decoupling dependency lists and build procedures from the dockerfiles, in order to hopefully favour contributions. See, for instance, https://github.com/hdl/containers/tree/pkg-file/debian-bullseye/gtkwave