let fs_spec =
  { file_docroot = base_dir^"/dcrt";
    file_uri = "/dcrt";
    file_suffix_types = [ 
      "css""text/css";
      "txt""text/plain";
      "html""text/html";
                        ];
    file_default_type = "application/octet-stream";
    file_options = [ 
      `Enable_gzip;
      `Enable_listings (simple_listing ?hide:None)
                   ]
  }