anchor.diff:  %% Tag resolution.
   %% -------------------------------------------------------------------
   
  -setup_default_tags(Parser) ->
  +setup_default_tags(#yaml_parser{options = Options} = Parser) ->
       Tags  = dict:new(),
       %% By default, "!" is resolved as "!" and the tag is considered
       %% local.
  
positive.code: 
  option_names() ->
      [
        doc_version,
        io_blocksize,
        token_fun
  
negative.code: check_options([]) ->
      ok.
  
  is_option_valid({default_tags, List}) when is_list(List) ->
      %% This fun() returns true for any invalid entries, to keep only
      %% those.
      Fun = fun
          ({{non_specific, A}, B}) ->
              not (io_lib:char_list(A) andalso io_lib:char_list(B));
          ({A, B}) ->
              not (io_lib:char_list(A) andalso io_lib:char_list(B));
          (_) ->
              true
      end,
      case lists:filter(Fun, List) of
          [] -> true;
          _  -> false
      end;
  is_option_valid({doc_version, {Major, Minor}}) when
    is_integer(Major) andalso Major >= 0 andalso
    is_integer(Minor) andalso Minor >= 0 ->
  