Resources

• Building a CalDAV client
• jsical reference
• CalConnect resources list
• CalConnect glossary

RFCs

(Support means support at the server level, not that we have all the features in the Calendar app or the groupware settings)

General RFCs

• ✅ Internet Calendaring and Scheduling Core Object Specification (iCalendar) (RFC 5545) (previously RFC 2445)
• ✅ Calendaring Extensions to WebDAV (CalDAV) (RFC 4791)
• ✅ New Properties for iCalendar (RFC 7986)
• ✅ Parameter Value Encoding in iCalendar and vCard (RFC 6868)

Specific features

• ✅ iCalendar Transport-Independent Interoperability Protocol (iTIP) (RFC 5546)
• ✅ iCalendar Message-Based Interoperability Protocol (iMIP) (RFC 6047)
• ✅ CalDAV Scheduling (RFC 6638)
• ✅ Calendaring Extensions to WebDAV (CalDAV): Time Zones by Reference (RFC 7809)
• ✅ Calendar Availability (RFC 7953)

Recent RFCs

• ❌ Calendaring Extensions to WebDAV (CalDAV): Managed Attachments (RFC 8607)
• ❌ Event Publishing Extensions to iCalendar (RFC 9073)
• ❌ "VALARM" Extensions for iCalendar (RFC 9074)
• ❌ Support for iCalendar Relationships (RFC 9253)

Upcoming Drafts

• JSCalendar: Converting from and to iCalendar (draft-ietf-calext-jscalendar-icalendar)
• Calendar subscription upgrades (draft-ietf-calext-subscription-upgrade)
• VPOLL: Consensus Scheduling Component for iCalendar (draft-ietf-calext-vpoll)

Abandonned drafts

• Support for Series in iCalendar (draft-ietf-calext-icalendar-series)
• Task Extensions to iCalendar (draft-apthorp-ical-tasks)
• Serverside Subscriptions (draft-ietf-calext-serverside-subscriptions-02)

Non-standard

• ❌ CalDAV: Calendar User Notifications
• ✅ Shared and Published Calendars in CalDAV Support from Sabre is based on an old abandoned draft (draft-pot-caldav-sharing-01 )
• ✅ Calendar User Proxy Functionality in CalDAV
• Apple has some more non-standard extensions in https://github.com/apple/ccs-calendarserver/tree/master/doc/Extensions
• Nextcloud's own specific properties https://github.com/nextcloud/calendar/wiki/Nextcloud-specific-properties