Set ``transient_view.get_top_widget()`` transient for
        ``self.``:meth:`get_top_widget`.

def set_transient(self, transient_view):
        """
        Set ``transient_view.get_top_widget()`` transient for
        ``self.``:meth:`get_top_widget`.
        """
        top = self.get_top_widget()
        if isinstance(top, (list, tuple)):
            for t in top:
                if t is not None:
                    transient_view.get_top_widget().set_transient_for(t)
        elif top is not None:
            transient_view.get_top_widget().set_transient_for(top)