behavior is to raise `ConfigValueValidationError` when the value
                is not of the right type. Useful when reading options from a
                file type that doesn't support as many types as Python.
            * `skip_unknown`: skip unknown configuration options. The default
                behaviour is to raise `ConfigUnknownOptionError`. Useful when
                reading options from a configuration file that has extra entries
                (e.g. for a later version of fontTools)
        N)