Calendaring Extensions (calext)

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The Calendaring Extensions working group is chartered to develop
extensions to the iCalendar (RFC 5545), iTIP (RFC 5546), and
CalDAV (RFC 4791) standards.

This working group will do the following:

- Develop an extension to iCalendar to support non-Gregorian recurrence
rules, without the need to support new calendar scale values in
iCalendar as a whole. This will allow for easy implementation of the
primary use case for non-Gregorian support in calendar systems, without
the need for significant changes to the iCalendar format. The
non-Gregorian calendar system should be based on the International
Components for Unicode work by the Unicode Consortium
(http://site.icu-project.org).

- Develop an extension to iCalendar to support a new component type that
allows users to express arbitrary, possibly repeating, periods of
"available" time. The primary use case for this is for users to express
their "office hours" (e.g., Monday-Friday, 9am-5pm) in a standard way to
ensure free busy lookups show the correct periods of availability.

- Define a set of new iCalendar properties and parameters to standardise
some existing experimental X- properties in common use, based on a
survey of existing implementations.

- Define a set of new iCalendar properties and parameters to cover key
uses cases that implementers have identified, including, but not
limited to, a new "IMAGE" property (to allow embedding/linking of
images tied to a specific event), and a "CONFERENCE" property (to allow
embedding information about dial-in numbers and similar multi-party
communication options for an event).

The working group will work under the following parameters:

- The extensions developed are expected to be backwards-compatible with
the existing calendar standards.  Incompatibilities must be identified,
minimized, and justified.

- For each set of extensions, examine their impact on the iTIP protocol
(RFC 5546), and define any necessary extensions to iTIP to accommodate
such impact.

- For each set of extensions, examine their impact on the CalDAV
protocol (RFC 4791), and define any necessary extensions to CalDAV to
accommodate such impact.  Interface with the httpbis working group to
ensure that any CalDAV changes are consistent with good http practices.

The working group will use the following drafts as initial input for its
work: 
draft-daboo-icalendar-rscale-03
draft-daboo-calendar-availability-05
draft-daboo-icalendar-extensions-08

The following are out of scope for the working group:

- Any change that impacts backwards compatibility with existing
deployed iCalendar/iTIP/CalDAV clients and servers will be discussed
by the working group with a view to minimizing disruption to deployed
implementations without compromising desirable new function.

- Any attempt to develop non-Gregorian calendar systems/calculations.