rra at stanford.edu
Wed Jun 6 21:20:06 UTC 2012
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
> (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?
> I got suspicious about this some months ago, but only got around to
> confirming the conflict last week. I'm a bit ashamed that I didn't
> notice it in time to influence RFC 3339, but in my defence I wasn't
> actually in the WG.
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 was a member of the RFC 2822 working group towards the end of the
process, but I think this was already well-settled before then. It is,
however, new in RFC 2822 compared to RFC 822. Appendix B of RFC 2822
lists it as a change from earlier standards:
7. Specifically allow and give meaning to "-0000" time zone.
RFC 822 (August 1982) allowed both -0000 and +0000 with the same meaning:
zone = "UT" / "GMT" ; Universal Time
; North American : UT
/ "EST" / "EDT" ; Eastern: - 5/ - 4
/ "CST" / "CDT" ; Central: - 6/ - 5
/ "MST" / "MDT" ; Mountain: - 7/ - 6
/ "PST" / "PDT" ; Pacific: - 8/ - 7
/ 1ALPHA ; Military: Z = UT;
; A:-1; (J not used)
; M:-12; N:+1; Y:+12
/ ( ("+" / "-") 4DIGIT ) ; Local differential
; hours+min. (HHMM)
(Note the notorious error in the definition of the military zones.) RFC
822 says that this form comes from ANSI X3.51-1975:
The other remaining two forms are taken from ANSI standard X3.51-1975.
One allows explicit indication of the amount of offset from UT; the
other uses common 3-character strings for indicating time zones in
This text is unchanged from RFC 733 (November 1977). A quick Google
search doesn't immediately reveal an online free copy of ANSI X3.51-1975.
Russ Allbery (rra at stanford.edu) <http://www.eyrie.org/~eagle/>
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