def _get_base_defaultLayer(self):
        """
        This is the environment implementation of
        :attr:`BaseFont.defaultLayer`. Return the
        default layer as a :class:`BaseLayer` object.
        The layer will be normalized with
        :func:`normalizers.normalizeLayer`.

        Subclasses must override this method.
        """
        name = self.defaultLayerName
        layer = self.getLayer(name)
        return layer