anchor.diff:  
   -define(PERCENT, 37).  % $\%
   -define(FULLSTOP, 46). % $\.
  +-define(LBRACE, 91). % $\[.
  +-define(RBRACE, 93). % $\].
   -define(IS_HEX(C), ((C >= $0 andalso C =< $9) orelse
                       (C >= $a andalso C =< $f) orelse
                       (C >= $A andalso C =< $F))).
  
positive.code: %%      is not safe. safe relative paths can be joined with an absolute path
  %%      and will result in a subdirectory of the absolute path.
  safe_relative_path("/" ++ _) ->
      undefined;
  safe_relative_path(P) ->
      safe_relative_path(P, []).
  
  safe_relative_path("", Acc) ->
      case Acc of
          [] ->
              "";
          _ ->
              string:join(lists:reverse(Acc), "/")
      end;
  safe_relative_path(P, Acc) ->
      case partition(P, "/") of
          {"", "/", _} ->
              %% /foo or foo//bar
              undefined;
          {"..", _, _} when Acc =:= [] ->
              undefined;
          {"..", _, Rest} ->
              safe_relative_path(Rest, tl(Acc));
          {Part, "/", ""} ->
              safe_relative_path("", ["", Part | Acc]);
          {Part, _, Rest} ->
              safe_relative_path(Rest, [Part | Acc])
      end.
  
  %% @spec shell_quote(string()) -> string()
  %% @doc Quote a string according to UNIX shell quoting rules, returns a string
  %%      surrounded by double quotes.
  shell_quote(L) ->
      shell_quote(L, [$\"]).
  
  %% @spec cmd_port([string()], Options) -> port()
  %% @doc open_port({spawn, mochiweb_util:cmd_string(Argv)}, Options).
  cmd_port(Argv, Options) ->
      open_port({spawn, cmd_string(Argv)}, Options).
  
  %% @spec cmd([string()]) -> string()
  %% @doc os:cmd(cmd_string(Argv)).
  cmd(Argv) ->
      os:cmd(cmd_string(Argv)).
  
  %% @spec cmd_string([string()]) -> string()
  %% @doc Create a shell quoted command string from a list of arguments.
  cmd_string(Argv) ->
      join([shell_quote(X) || X <- Argv], " ").
  
  %% @spec join([string()], Separator) -> string()
  %% @doc Join a list of strings together with the given separator
  %%      string or char.
  join([], _Separator) ->
      [];
  join([S], _Separator) ->
      lists:flatten(S);
  join(Strings, Separator) ->
      lists:flatten(revjoin(lists:reverse(Strings), Separator, [])).
  
  revjoin([], _Separator, Acc) ->
      Acc;
  revjoin([S | Rest], Separator, []) ->
      revjoin(Rest, Separator, [S]);
  revjoin([S | Rest], Separator, Acc) ->
      revjoin(Rest, Separator, [S, Separator | Acc]).
  
  %% @spec quote_plus(atom() | integer() | float() | string() | binary()) -> string()
  %% @doc URL safe encoding of the given term.
  quote_plus(Atom) when is_atom(Atom) ->
      quote_plus(atom_to_list(Atom));
  quote_plus(Int) when is_integer(Int) ->
      quote_plus(integer_to_list(Int));
  quote_plus(Binary) when is_binary(Binary) ->
      quote_plus(binary_to_list(Binary));
  quote_plus(Float) when is_float(Float) ->
      quote_plus(mochinum:digits(Float));
  quote_plus(String) ->
      quote_plus(String, []).
  
  quote_plus([], Acc) ->
      lists:reverse(Acc);
  quote_plus([C | Rest], Acc) when ?QS_SAFE(C) ->
      quote_plus(Rest, [C | Acc]);
  quote_plus([$\s | Rest], Acc) ->
      quote_plus(Rest, [$+ | Acc]);
  quote_plus([C | Rest], Acc) ->
      <<Hi:4, Lo:4>> = <<C>>,
      quote_plus(Rest, [hexdigit(Lo), hexdigit(Hi), ?PERCENT | Acc]).
  
  %% @spec urlencode([{Key, Value}]) -> string()
  %% @doc URL encode the property list.
  urlencode(Props) ->
      RevPairs = lists:foldl(fun ({K, V}, Acc) ->
                                     [[quote_plus(K), $=, quote_plus(V)] | Acc]
                             end, [], Props),
      lists:flatten(revjoin(RevPairs, $&, [])).
  
  %% @spec parse_qs(string() | binary()) -> [{Key, Value}]
  %% @doc Parse a query string or application/x-www-form-urlencoded.
  parse_qs(Binary) when is_binary(Binary) ->
      parse_qs(binary_to_list(Binary));
  parse_qs(String) ->
      parse_qs(String, []).
  
  parse_qs([], Acc) ->
      lists:reverse(Acc);
  parse_qs(String, Acc) ->
      {Key, Rest} = parse_qs_key(String),
      {Value, Rest1} = parse_qs_value(Rest),
      parse_qs(Rest1, [{Key, Value} | Acc]).
  
  parse_qs_key(String) ->
      parse_qs_key(String, []).
  
  parse_qs_key([], Acc) ->
      {qs_revdecode(Acc), ""};
  parse_qs_key([$= | Rest], Acc) ->
      {qs_revdecode(Acc), Rest};
  parse_qs_key(Rest=[$; | _], Acc) ->
      {qs_revdecode(Acc), Rest};
  parse_qs_key(Rest=[$& | _], Acc) ->
      {qs_revdecode(Acc), Rest};
  parse_qs_key([C | Rest], Acc) ->
      parse_qs_key(Rest, [C | Acc]).
  
  parse_qs_value(String) ->
      parse_qs_value(String, []).
  
  parse_qs_value([], Acc) ->
      {qs_revdecode(Acc), ""};
  parse_qs_value([$; | Rest], Acc) ->
      {qs_revdecode(Acc), Rest};
  parse_qs_value([$& | Rest], Acc) ->
      {qs_revdecode(Acc), Rest};
  parse_qs_value([C | Rest], Acc) ->
      parse_qs_value(Rest, [C | Acc]).
  
  %% @spec unquote(string() | binary()) -> string()
  %% @doc Unquote a URL encoded string.
  unquote(Binary) when is_binary(Binary) ->
      unquote(binary_to_list(Binary));
  unquote(String) ->
      qs_revdecode(lists:reverse(String)).
  
  qs_revdecode(S) ->
      qs_revdecode(S, []).
  
  qs_revdecode([], Acc) ->
      Acc;
  qs_revdecode([$+ | Rest], Acc) ->
      qs_revdecode(Rest, [$\s | Acc]);
  qs_revdecode([Lo, Hi, ?PERCENT | Rest], Acc) when ?IS_HEX(Lo), ?IS_HEX(Hi) ->
      qs_revdecode(Rest, [(unhexdigit(Lo) bor (unhexdigit(Hi) bsl 4)) | Acc]);
  qs_revdecode([C | Rest], Acc) ->
      qs_revdecode(Rest, [C | Acc]).
  
  %% @spec urlsplit(Url) -> {Scheme, Netloc, Path, Query, Fragment}
  %% @doc Return a 5-tuple, does not expand % escapes. Only supports HTTP style
  %%      URLs.
  urlsplit(Url) ->
      {Scheme, Url1} = urlsplit_scheme(Url),
      {Netloc, Url2} = urlsplit_netloc(Url1),
      {Path, Query, Fragment} = urlsplit_path(Url2),
      {Scheme, Netloc, Path, Query, Fragment}.
  
  urlsplit_scheme(Url) ->
      urlsplit_scheme(Url, []).
  
  urlsplit_scheme([], Acc) ->
      {"", lists:reverse(Acc)};
  urlsplit_scheme(":" ++ Rest, Acc) ->
      {string:to_lower(lists:reverse(Acc)), Rest};
  urlsplit_scheme([C | Rest], Acc) ->
      urlsplit_scheme(Rest, [C | Acc]).
  
  urlsplit_netloc("//" ++ Rest) ->
      urlsplit_netloc(Rest, []);
  urlsplit_netloc(Path) ->
      {"", Path}.
  
  urlsplit_netloc(Rest=[C | _], Acc) when C =:= $/; C =:= $?; C =:= $# ->
      {lists:reverse(Acc), Rest};
  urlsplit_netloc([C | Rest], Acc) ->
      urlsplit_netloc(Rest, [C | Acc]).
  
  
  %% @spec path_split(string()) -> {Part, Rest}
  
negative.code: %%      partition("foo/bar", "/") = {"foo", "/", "bar"},
  %%      partition("foo", "/") = {"foo", "", ""}.
  partition(String, Sep) ->
    case partition(String, Sep, []) of
      undefined ->
        {String, "", ""};
      Result ->
        Result
    end.
  
  partition("", _Sep, _Acc) ->
    undefined;
  partition(S, Sep, Acc) ->
    case partition2(S, Sep) of
      undefined ->
        [C | Rest] = S,
        partition(Rest, Sep, [C | Acc]);
      Rest ->
        {lists:reverse(Acc), Sep, Rest}
    end.
  
  partition2(Rest, "") ->
    Rest;
  partition2([C | R1], [C | R2]) ->
    partition2(R1, R2);
  partition2(_S, _Sep) ->
    undefined.
  
  
  
  