protected function define_submission_subplugin_structure() {

        return false; // This subplugin backup is only one example. Skip it.

        // remember this has not XML representation
        $subplugin = $this->get_subplugin_element(null, '/assignment/assignmenttype', 'offline');

        // type of the subplugin, name of the subplugin and name of the connection point (recommended)
        $asssuboff = new backup_nested_element($this->get_recommended_name());
        // Why 'submission_config' name? Because it must be unique in the hierarchy and we
        // already are using 'config' above withing the same file
        $config = new backup_nested_element('submission_config', null, array('name', 'value'));

        $subplugin->add_child($asssuboff);
        $asssuboff->add_child($config);

        $config->set_source_table('config', array('id' => backup::VAR_PARENTID));

        return $subplugin; // And we return the root subplugin element
    }