[tz] -00:00

Alan Barrett apb at cequrux.com
Thu Jun 7 06:45:12 UTC 2012

On Wed, 06 Jun 2012, Russ Allbery wrote:
>Zefram <zefram at fysh.org> writes:
>> Speaking of this, did anyone else notice that
>> (a) ISO 8601 requires a zero offset to be denoted with a "+" sign,
>>     forbidding "-00" (ISO 8601:2000 clause 5.1.1 or ISO 8601:2004 clause
>>     3.4.2), and

Since ISO 8601 is not freely available (or at least was not freely 
available years ago), and the freely-available summaries did not 
mention this, no, I had not noticed.

>> (b) RFC 3339 is supposedly a profile of ISO 8601, and
>> (c) RFC 3339 *does* allow "-00", denoting the same offset as "+00",
>>     but connoting that it's not specifying a preferred offset?
>This convention didn't originate from RFC 3339.  It comes from RFC 2822
>(published April 2001 but in progress long, long before that):
>   The form "+0000" SHOULD be used to indicate a time zone at Universal
>   Time.  Though "-0000" also indicates Universal Time, it is used to
>   indicate that the time was generated on a system that may be in a local
>   time zone other than Universal Time and therefore indicates that the
>   date-time contains no information about the local time zone.

I think that RFC 2822 got that from a convention that was first 
advocated by Dan Bernstein in 1996.  The oldest references 
that I was easily able to find are from March 1996:

A message from djb at koobera.math.uic.edu (D. J. Bernstein)
to the DRUMS mailing list (which was working on what became RFC 
2822):  <http://notabug.com/2002/drums-archive/1320>

     The time shown MUST be the sender's local time. Exception: the
     zone -0000 indicates that the local time is unavailable or
     meaningless, and that the time shown is the actual time. (In
     contrast, the zone +0000 indicates that the time shown is both
     local time and actual time.)

and an entry in the qmail CHANGES file 

19960325 change: time zone is now -0000 instead of +0000. encouraging
          DRUMS to use this as an i-don't-know-the-local-time indicator.

--apb (Alan Barrett)

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