Backup and restore

It depends of whether you need to attach your local plugin's data to the course, the section or a module instance in the backup. Given that your plugin is called local_foobar, the following should work (not tested) to attach your plugin's data to other modules' data.

// backup/moodle2/backup_local_foobar_plugin.class.php

class backup_local_foobar_plugin extends backup_local_plugin {

    /**
     * Returns the information to be attached to a module instance
     */
    protected function define_module_plugin_structure() {

        $plugin = $this->get_plugin_element();
        $foobar = new backup_nested_element($this->get_recommended_name());
        $plugin->add_child($filterurlresource);

        // Continue here to add more child elements to your $foobar and
        // set their data source as normally.
    }
}

For an example of how to attach your plugin's data to a course and section, see e.g. this file - it is for a course format but it should work similarly AFAIK.

Hey Ray, in looking at your code, it seems like you are on the right track.  I think what is causing the error is this line:

$plugin = $this->get_plugin_element(null, $this->get_include_condition(), 'include');

I haven't use those condition parameters before and I really don't know what they are all about.  I think you are trying to see if the question is included in the backup or not, but by the time your hook is being called, the question is being written out to the backup, so it is included.  Maybe try just removing all the parameters here like in David's post.