Outpust a machine readable site map for search engines and robots. Supports the following formats: Sitemap Protocol used by Google Sitemaps. List of URLs in text format (e.g. Yahoo! submission). Another option is to output an unordered list (HTML: UL/LI) to show the sitemap on your webpage.
Documentation is available in MODx wiki article SiteMap: Google sitemaps in MODx - http://wiki.modxcms.com/index.php/SiteMap:_Google_sitemaps_in_MODx