'Return a new app_iter built from the response app_iter, that
serves up only the given ``start:stop`` range.'

def app_iter_range(self, start, stop):

    app_iter = self._app_iter
    if hasattr(app_iter, 'app_iter_range'):
        return app_iter.app_iter_range(start, stop)
    return AppIterRange(app_iter, start, stop)
