@classmethod
def pyramid(cls, cfg, schema, changer):
    """ pyramid password changer registration directive.

        :param schema: Principal uri schema.
        :param changer: Function

        .. code-block:: python

          config = Configurator()
          config.include('ptah')

          config.ptah_password_changer('custom-schema', custom_changer)
        """
    cls(schema, 3)(changer, cfg)
