Hi Ulrich,

> On 20. Oct 2022, at 08:27, Ulrich Windl <[email protected]> 
> wrote:
> 
> Interestingly I found the complement of "-0000" in RFC 5545 (iCalendar, "FORM
> #1: DATE WITH LOCAL TIME" (page 33), claiming to be based on [ISO.8601.2004]):
> "DATE-TIME values of this type are said to be "floating" and are not bound to
> any time zone in particular.  They are used to represent the same hour, 
> minute,
> and second value regardless of which time zone is currently being observed. 
> For example, an event can be defined that indicates that an individual will be
> busy from 11:00 AM to 1:00 PM every day, no matter which time zone the person
> is in.  In these cases, a local time can be specified.”

The concept of a “floating time” very much exists.
A floating time, however, is not a timestamp in the RFC 3339 sense: it is not 
referring to a specific instant in time.
A floating time depends on the context to derive such an instant.
It is more of a calendaring concept, and it is no surprise that you found this 
discussion in a calendaring standard.

Floating times were deemed out of scope for the SEDATE work.

Note that CBOR has a couple of tags for what could analogously be called a 
"floating date”, see RFC 8943.
These are useful as a commercial concept that is in wide use in documents such 
as passports.
I could certainly imagine providing a way to identify a floating time via a 
CBOR tag as well, but this would be separate from the timestamp concept 
provided by draft-ietf-core-time-tag.

Grüße, Carsten

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