def flattened():
    """Return an iterator of all included and extended interfaces

        An iterator is returned for all interfaces either included in
        or extended by interfaces included in the specifications
        without duplicates. The interfaces are in "interface
        resolution order". The interface resolution order is such that
        base interfaces are listed after interfaces that extend them
        and, otherwise, interfaces are included in the order that they
        were defined in the specification.
        """
