let () =
  let test_file = "validator/tests/html/attributes/lang/missing-lang-attribute-haswarn.html" in
  let ic = open_in test_file in
  let html = really_input_string ic (in_channel_length ic) in
  close_in ic;
  let reader = Bytesrw.Bytes.Reader.of_string html in
  let doc = Html5rw.parse ~collect_errors:true reader in
  let root = Html5rw.root doc in
  print_endline "=== DOM Structure (with namespaces) ===";
  let rec print_node indent (node : Html5rw.Dom.node) =
    let open Html5rw.Dom in
    match node.name with
    | "#text" -> ()
    | "#document" | "#document-fragment" ->
        Printf.printf "%s%s\n" indent node.name;
        List.iter (print_node (indent ^ "  ")) node.children
    | "!doctype" -> ()
    | "#comment" -> ()
    | _ ->
        let ns = match node.namespace with Some ns -> ns | None -> "none" in
        Printf.printf "%s<%s ns=%s>\n" indent node.name ns;
        List.iter (fun (k, v) ->
          if k = "foo" then Printf.printf "%s  @%s=%s\n" indent k v
        ) node.attrs;
        List.iter (print_node (indent ^ "  ")) node.children
  in
  print_node "" root;
  print_endline "\n=== Checking... ===";
  let reader2 = Bytesrw.Bytes.Reader.of_string html in
  let result = Html5_checker.check ~collect_parse_errors:true ~system_id:test_file reader2 in
  let errors = Html5_checker.errors result in
  let warnings = Html5_checker.warnings result in
  print_endline "=== Errors ===";
  List.iter (fun e -> print_endline e.Html5_checker.Message.message) errors;
  print_endline "\n=== Warnings ===";
  List.iter (fun e -> print_endline e.Html5_checker.Message.message) warnings;
  print_endline "\n=== Expected ===";
  print_endline "Consider adding a \xe2\x80\x9clang\xe2\x80\x9d attribute to the \xe2\x80\x9chtml\xe2\x80\x9d start tag to declare the language of this document."