anchor.diff:  -spec of_props(t_props()) ->
       hope_result:t(t(credentials_type()), parsing_error()).
   of_props(Props) ->
  +    % TODO: Check for all missing fields, not just the first.
       MakeFieldGetter =
           fun (Key) ->
               fun (Acc) ->
  
positive.code:     ;   {ok, Value} ->
              case of_bin(Value)
              of  {error, {data_format_invalid, _}=ParsingError} ->
                      {error, {internal, ParsingError}}
              ;   {ok, #t{expiry=ExpiryOpt}=T} ->
                      ExpiryToOkOrError =
  
negative.code:     }.
  
  -type parsing_error() ::
        {data_format_invalid, binary()}
      | {field_missing      , binary()}
      .
  
  -type retrival_error() ::
        {internal, parsing_error()}
  