public function make_toggle($key) {
        $attrs = array('href' => '#');

        // Do proper lang strings for title attributes exist for the given key?
        $strmanager = \get_string_manager();
        $titleall = get_string('all');
        $titlenone = get_string('none');
        if ($strmanager->string_exists(strtolower($key) . 'all', 'gradereport_singleview')) {
            $titleall = get_string(strtolower($key) . 'all', 'gradereport_singleview');
        }
        if ($strmanager->string_exists(strtolower($key) . 'none', 'gradereport_singleview')) {
            $titlenone = get_string(strtolower($key) . 'none', 'gradereport_singleview');
        }

        $all = html_writer::tag('a', get_string('all'), $attrs + array(
            'class' => 'include all ' . $key,
            'title' => $titleall
        ));

        $none = html_writer::tag('a', get_string('none'), $attrs + array(
            'class' => 'include none ' . $key,
            'title' => $titlenone
        ));

        return html_writer::tag('span', "$all / $none", array(
            'class' => 'inclusion_links'
        ));
    }