Libical RFC calendar standards support

Libical implements the RFCS:

RFC5545 Internet Calendaring and Scheduling Core Object Specification (iCalendar)
RFC5546 iCalendar Transport-Independent Interoperability Protocol (iTIP)
RFC7529 Non-Gregorian Recurrence Rules in the Internet Calendaring and Scheduling Core Object Specification (iCalendar)

as well as iCalendar extensions described in:

RFC7986 New Properties for iCalendar
RFC9073 Event Publishing Extensions to iCalendar
RFC9074 "VALARM" Extensions for iCalendar
RFC9253 Support for iCalendar Relationships

Plus:

RFC6047 iCalendar Message-Based Interoperability Protocol (iMIP)
RFC6638 Scheduling Extensions to CalDAV