anchor.diff:                  {file, <<"undefined">>},
                   {host, <<"localhost">>},
                   {facility, <<"erlang">>},
  -                {'_pid', <<"unknown">>},
  -                {'_node', <<"undefined">>},
  -                {'_application', <<"lager_graylog_backend">>},
  -                {'_module', <<"undefined">>},
  -                {'_function', <<"undefined">>}
  +                {<<"_pid">>, <<"unknown">>},
  +                {<<"_node">>, <<"undefined">>},
  +                {<<"_application">>, <<"lager_graylog_backend">>},
  +                {<<"_module">>, <<"undefined">>},
  +                {<<"_function">>, <<"undefined">>}
                  ],
   
       ?assertEqual(lists:sort(Expected), lists:sort(Data)).
  
positive.code: get_pid(_) ->
      <<"malformed">>.
  
  format_metadata({pid, V}) ->
      {'_pid', get_pid(V)};
  format_metadata({K, V}) when is_binary(V) ->
      {additional_field_name(K), V};
  format_metadata({K, V}) ->
  
negative.code:     {additional_field_name(K), F}.
  
  additional_field_name(N) when is_atom(N) ->
      F = atom_to_binary(N, utf8),
      <<"_", F/binary>>.
  
  syslog_severity(debug) ->
      7;
  