plaster is a loader interface around multiple config file formats. It exists to define a common API for applications to use when they wish to load configuration. The library itself does not aim to handle anything except a basic API that applications may use to find and load configuration settings. Any specific constraints should be implemented in a pluggable loader which can be registered via an entrypoint.
See https://docs.pylonsproject.org/projects/plaster/en/latest/ or docs/index.rst in this distribution for detailed documentation.