public function col_select(\tool_monitor\rule $rule) {
        global $OUTPUT;

        $options = $rule->get_subscribe_options($this->courseid);
        $text = get_string('subscribeto', 'tool_monitor', $rule->get_name($this->context));

        if ($options instanceof \single_select) {
            $options->set_label($text, array('class' => 'accesshide'));
            return $OUTPUT->render($options);
        } else if ($options instanceof \moodle_url) {
            // A \moodle_url to subscribe.
            $icon = $OUTPUT->pix_icon('t/add', $text);
            $link = new \action_link($options, $icon);
            return $OUTPUT->render($link);
        } else {
            return $options;
        }
    }