Serialising Extended Data About Times and Events
charter-ietf-sedate-01-00

RFC 3339 defines a text format as a profile of ISO 8601 that can reliably
express an instant in time, either in UTC or in a local time along with the
offset against UTC. However, datetime data often has additional context, such
as the timezone or calendar system that was in use when that instant was
recorded.

Particularly when using times for interval, recurrence, or offset calculations,
it is necessary to know the context in which the timepoint exists. It would be
valuable to have a standard text serialisation format for this contextual data.
This working group will develop and publish a format meeting that requirement,
subject to the additional constraints described below.

* This format must be able to round-trip through intermediate systems which do
not understand the full context.

* Systems which don’t understand all the contextual fields must still be able
to reliably extract the instant in time.

This format will be a companion to RFC 3339 rather than a replacement,
embedding unaltered RFC 3339 data in a way that makes it easy to parse just the
datetime data independently of the context.

The work on this format discovered an issue with RFC 3339. When ISO 8601 was
revised in 2000, the “-00:00” offset which RFC 3339 had invented for “offset
isn’t relevant” was made invalid. This means that RFC 3339 is not a strict
subset of the current version of ISO 8601.

To fix this issue, the working group will additionally update RFC 3339 by
removing the definition of “-00:00” and updating the definition of “Z” (Zulu)
to mean that the offset to local time is not known, leaving “+00:00” to mean
that UTC is the preferred reference point for local time.

Any other changes to RFC 3339 are explicitly outside the charter for this
working group. If a need for any other changes to RFC 3339 emerges, this group
must recharter before performing that work. In this case, the changes to RFC
3339 will need to be clearly motivated, evaluated and precisely scoped during
the rechartering process, and will need to make only changes that keep the
timestamp specification a profile of current versions of ISO 8601. Stability of
the RFC 3339 timestamp format is important to existing IETF protocols and the
Internet generally, and any rechartering process should frown on anything that
would invalidate the existing timestamp format.

The working group will coordinate with ECMA International TC39 and ISO/TC 154
to ensure that this work remains a strict extension of ISO 8601 and its various
parts rather than becoming a conflicting standard.