@classmethod
def validate(cls, **kwargs):
    """
        Validate the keyword arguments and return the (converted) kwargs
        dictionary.

        You should override this method if you want to enable validation
        of your attributes.

        Notes
        -----
        One doesn't need to validate the following things, as it is already
        take care of by the `MultiState` class:

        - Check that each argument is assigned with a default.
        - Check that the kwargs keys are in _attributes tuple.
        """
    return kwargs
