anchor.diff:  %%% Limitations:
   %%% - #!fold-case and #!no-fold-case are not yet implemented
   %%% - "#u8(" for the <bytevector> syntax is not yet implemented
  -%%% - only supports the ASCII character set, embedded in 8-bit characters
   %%% - the polar, rectangular, and rational number syntaxes are not supported
   %%%
   %%% Extensions:
  
positive.code:       io_lib:format("invalid character: ~p", [Ch]);
      {invalid_character_name, Str} ->
        io_lib:format("invalid character name: ~s", [Str]);
      {invalid_hex_character_value, Num} ->
        io_lib:format("invalid hex character value: ~p", [Num]);
      {invalid_identifier, Str} ->
        io_lib:format("invalid identifier: ~s", [Str]);
      {invalid_identifier, Str, Ch} ->
  
negative.code: 
  scan_vi_backslash(LI, Acc) ->
    case scan_inline_escape(LI) of
      Ch when is_integer(Ch) ->
        scan_vi(LI, [Ch | Acc]);
      {error, Ch} ->
        lexer_error({invalid_character, Ch})
    end.
  