Contao\Module::renderNavigation PHP Method

    protected function renderNavigation($pid, $level = 1, $host = null, $language = null)
    {
        // Get all active subpages
        $objSubpages = \PageModel::findPublishedSubpagesWithoutGuestsByPid($pid, $this->showHidden, $this instanceof ModuleSitemap);
        if ($objSubpages === null) {
            return '';
        }
        $items = array();
        $groups = array();
        // Get all groups of the current front end user
        if (FE_USER_LOGGED_IN) {
            $this->import('FrontendUser', 'User');
            $groups = $this->User->groups;
        }
        // Layout template fallback
        if ($this->navigationTpl == '') {
            $this->navigationTpl = 'nav_default';
        }
        /** @var FrontendTemplate|object $objTemplate */
        $objTemplate = new \FrontendTemplate($this->navigationTpl);
        $objTemplate->pid = $pid;
        $objTemplate->type = get_class($this);
        $objTemplate->cssID = $this->cssID;
        // see #4897
        $objTemplate->level = 'level_' . $level++;
        /** @var PageModel $objPage */
        global $objPage;
        // Browse subpages
        foreach ($objSubpages as $objSubpage) {
            // Skip hidden sitemap pages
            if ($this instanceof ModuleSitemap && $objSubpages->sitemap == 'map_never') {
                continue;
            }
            $subitems = '';
            $_groups = \StringUtil::deserialize($objSubpage->groups);
            // Override the domain (see #3765)
            if ($host !== null) {
                $objSubpage->domain = $host;
            }
            // Do not show protected pages unless a front end user is logged in
            if (!$objSubpage->protected || is_array($_groups) && count(array_intersect($_groups, $groups)) || $this->showProtected || $this instanceof ModuleSitemap && $objSubpage->sitemap == 'map_always') {
                // Check whether there will be subpages
                if ($objSubpage->subpages > 0 && (!$this->showLevel || $this->showLevel >= $level || !$this->hardLimit && ($objPage->id == $objSubpage->id || in_array($objPage->id, $this->Database->getChildRecords($objSubpage->id, 'tl_page'))))) {
                    $subitems = $this->renderNavigation($objSubpage->id, $level, $host, $language);
                }
                $href = null;
                // Get href
                switch ($objSubpage->type) {
                    case 'redirect':
                        $href = $objSubpage->url;
                        if (strncasecmp($href, 'mailto:', 7) === 0) {
                            $href = \StringUtil::encodeEmail($href);
                        }
                        break;
                    case 'forward':
                        if ($objSubpage->jumpTo) {
                            /** @var PageModel $objNext */
                            $objNext = $objSubpage->getRelated('jumpTo');
                        } else {
                            $objNext = \PageModel::findFirstPublishedRegularByPid($objSubpage->id);
                        }
                        // Hide the link if the target page is invisible
                        if (!$objNext instanceof PageModel || !$objNext->published || $objNext->start != '' && $objNext->start > time() || $objNext->stop != '' && $objNext->stop < time()) {
                            continue 2;
                        }
                        $href = $objNext->getFrontendUrl();
                        break;
                    default:
                        $href = $objSubpage->getFrontendUrl();
                        break;
                }
                $row = $objSubpage->row();
                $trail = in_array($objSubpage->id, $objPage->trail);
                // Active page
                if (($objPage->id == $objSubpage->id || $objSubpage->type == 'forward' && $objPage->id == $objSubpage->jumpTo) && !$this instanceof ModuleSitemap && $href == \Environment::get('request')) {
                    // Mark active forward pages (see #4822)
                    $strClass = ($objSubpage->type == 'forward' && $objPage->id == $objSubpage->jumpTo ? 'forward' . ($trail ? ' trail' : '') : 'active') . ($subitems != '' ? ' submenu' : '') . ($objSubpage->protected ? ' protected' : '') . ($objSubpage->cssClass != '' ? ' ' . $objSubpage->cssClass : '');
                    $row['isActive'] = true;
                    $row['isTrail'] = false;
                } else {
                    $strClass = ($subitems != '' ? 'submenu' : '') . ($objSubpage->protected ? ' protected' : '') . ($trail ? ' trail' : '') . ($objSubpage->cssClass != '' ? ' ' . $objSubpage->cssClass : '');
                    // Mark pages on the same level (see #2419)
                    if ($objSubpage->pid == $objPage->pid) {
                        $strClass .= ' sibling';
                    }
                    $row['isActive'] = false;
                    $row['isTrail'] = $trail;
                }
                $row['subitems'] = $subitems;
                $row['class'] = trim($strClass);
                $row['title'] = \StringUtil::specialchars($objSubpage->title, true);
                $row['pageTitle'] = \StringUtil::specialchars($objSubpage->pageTitle, true);
                $row['link'] = $objSubpage->title;
                $row['href'] = $href;
                $row['nofollow'] = strncmp($objSubpage->robots, 'noindex,nofollow', 16) === 0;
                $row['target'] = '';
                $row['description'] = str_replace(array("\n", "\r"), array(' ', ''), $objSubpage->description);
                // Override the link target
                if ($objSubpage->type == 'redirect' && $objSubpage->target) {
                    $row['target'] = ' target="_blank"';
                }
                $items[] = $row;
            }
        }
        // Add classes first and last
        if (!empty($items)) {
            $last = count($items) - 1;
            $items[0]['class'] = trim($items[0]['class'] . ' first');
            $items[$last]['class'] = trim($items[$last]['class'] . ' last');
        }
        $objTemplate->items = $items;
        return !empty($items) ? $objTemplate->parse() : '';
    }