function topNav($menu_set=false) {
        global $CFG, $LAUNCH;
        $sess_key = 'tsugi_top_nav_'.$CFG->wwwroot;
        $launch_return_url = $LAUNCH->ltiRawParameter('launch_presentation_return_url', false);

        $same_host = false;
        if ( $CFG->apphome && startsWith($launch_return_url, $CFG->apphome) ) $same_host = true;
        if ( $CFG->wwwroot && startsWith($launch_return_url, $CFG->wwwroot) ) $same_host = true;

        // Canvas bug: launch_target is iframe even in new window (2017-01-10)
        $launch_target = LTIX::ltiRawParameter('launch_presentation_document_target', false);
        if ( $menu_set === false && $this->session_get($sess_key) ) {
            $menu_set = \Tsugi\UI\MenuSet::import($this->session_get($sess_key));
        } else if ( $menu_set === true ) {
            $menu_set = self::defaultMenuSet();
        } else if ( $same_host && $launch_return_url ) {
            // If we are in an iframe we will be hidden
            $menu_set = self::returnMenuSet($launch_return_url);
        } else if ( $launch_target !== false && strtolower($launch_target) == 'window' ) {
            $menu_set = self::closeMenuSet();
        // Since Coursers sets precious little
        } else if ( $LAUNCH->isCoursera() ) {
            $menu_set = self::closeMenuSet();
        // Since canvas does not set launch_target properly
        } else if ( $launch_target !== false && ( $LAUNCH->isCanvas() || $LAUNCH->isCoursera() ) ) {
            $menu_set = self::closeMenuSet();
        } else if ( $launch_return_url !== false ) {
            $menu_set = self::returnMenuSet($launch_return_url);
        }

        // Always put something out if we are an outer page - in an iframe, it will be hidden
        if ( $menu_set === false && defined('COOKIE_SESSION') ) {
            $menu_set = self::defaultMenuSet();
        }

        if ( $menu_set === false ) {
            $menu_set = self::closeMenuSet();
        }

        $menu_txt = self::menuNav($menu_set);
        if ( $this->buffer ) return $menu_txt;
        echo($menu_txt);
    }