anchor.diff:  to_3339(Date, secs) when is_tuple(Date) ->
       Epoch = calendar_to_secs(Date),
       true = is_integer(Epoch),
  -    to_3339(Epoch, secs).
  +    to_3339(Epoch, secs);
  +
  +to_3339(_, _) ->
  +    {error, date_invalid}.
   
   
   %% @doc Converts an incoming epoch or rfc3339 to normalized epoch
  
positive.code:     rfc3339:to_time(to_bin(Date), to_erlang_unit(Unit));
  
  to_epoch(Date, secs) when is_tuple(Date) ->
      {ok, calendar_to_secs(Date)}.
  
  
  %% @doc Converts an incoming epoch or rfc3339 to normalized epoch
  
negative.code:     end;
  
  to_calendar(Date) when is_tuple(Date) ->
      {ok, Date};
  
  to_calendar(_) ->
      {error, date_invalid}.
  
  
  %% @doc Quick 3339 parser (only for Z timezone)
  