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.