@classmethod
def _get_default(cls, attribute):
    """Return the default value for `attribute`.

        If no default is specified in this style, get the default from the
        nearest superclass.
        If `attribute` is not supported, raise a :class:`KeyError`."""
    try:
        for klass in cls.__mro__:
            if attribute in klass._attributes:
                return klass._attributes[attribute].default_value
    except AttributeError:
        raise KeyError("No attribute '{}' in {}".format(attribute, cls))
