anchor.diff:       {'Shutdown',                   <<"503">>},
        {'TooManyRequests',            <<"429">>},
        {'TopicDisallowed',            <<"400">>},
  -     {'Unregistered',               <<"400">>},
  +     {'Unregistered',               <<"410">>},
        {success,                      <<"200">>}
       ].
   
  
positive.code:      {'BadPath',                    <<"400">>},
       {'BadPriority',                <<"400">>},
       {'BadTopic',                   <<"400">>},
       {'DeviceTokenNotForTopic',     <<"410">>},
       {'DuplicateHeaders',           <<"400">>},
       {'Forbidden',                  <<"400">>},
       {'IdleTimeout',                <<"503">>},
  
negative.code:         {<<"200">>, <<>>} ->
              {{<<":status">>, <<"200">>}, undefined};
          {<<SC/binary>>, <<>>} when SC /= <<>> ->
              Rsn = reason_for_status_code(SC),
              status_hdr(Rsn, S#?S.sts_hdrs);
          {<<>>, <<Rsn/binary>>} when Rsn /= <<>> ->
              status_hdr(b2a(Rsn), S#?S.sts_hdrs);
          {<<SC/binary>>, <<Rsn/binary>>} ->
              encode_status_hdr({<<":status">>, SC}, b2a(Rsn))
      end.
  
  %%--------------------------------------------------------------------
  