docs: def sitemap_index(request):
      """Return a sitemap index xml file for search engines."""
      sitemaps = []
      with db_connect() as db_connection:
          with db_connection.cursor() as cursor:
              cursor.execute("""\
                  SELECT authors[1], max(revised)
                  FROM latest_modules
                  WHERE portal_type NOT IN ('CompositeModule', 'SubCollection')
                  GROUP BY authors[1]
              """)
  
              for author, revised in cursor.fetchall():
                  sitemaps.append(Sitemap(url=request.route_url(
                      'sitemap', from_id=author),
                      lastmod=revised))
  
      si = SitemapIndex(sitemaps=sitemaps)
      resp = request.response
      resp.status = '200 OK'
      resp.content_type = 'text/xml'
      resp.body = si()
      return resp