public function render_preferences_group(preferences_group $renderable) {
        $html = '';
        $html .= html_writer::start_tag('div', array('class' => 'col-sm-4 preferences-group'));
        $html .= $this->heading($renderable->title, 3);
        $html .= html_writer::start_tag('ul');
        foreach ($renderable->nodes as $node) {
            if ($node->has_children()) {
                debugging('Preferences nodes do not support children', DEBUG_DEVELOPER);
            }
            $html .= html_writer::tag('li', $this->render($node));
        }
        $html .= html_writer::end_tag('ul');
        $html .= html_writer::end_tag('div');
        return $html;
    }