RFC 7529 - non gregorian RRULE

[niccokunzmann]

RFC 7529 updates iCalendar [RFC5545] [...] to extend the "RRULE" property definition.

In order to support this standard, we should make sure that we support

• parsing the examples mentioned
• creating the examples
• make sure ICS -> icalendar -> ICS works

The "RRULE" property is extended to include an "RSCALE" element in its value

DTSTART;VALUE=DATE:20130210
RRULE:RSCALE=CHINESE;FREQ=YEARLY
SUMMARY:Chinese New Year

Month numbers can include an "L" suffix

A "SKIP" element is added

DTSTART;VALUE=DATE:20130906
RRULE:RSCALE=ETHIOPIC;FREQ=MONTHLY;BYMONTH=13
SUMMARY:First day of 13th month

DTSTART;VALUE=DATE:20140208
RRULE:RSCALE=HEBREW;FREQ=YEARLY;BYMONTH=5L;BYMONTHDAY=8;SKIP=FORWARD
SUMMARY:Anniversary

DTSTART;VALUE=DATE:20120229
RRULE:RSCALE=GREGORIAN;FREQ=YEARLY;SKIP=FORWARD
SUMMARY:Anniversary

This specification uses the Unicode Consortium's registry of calendar
systems [UNICODE.CLDR] to define valid values for the "RSCALE" element of an "RRULE".

See also

• Claiming compatibility to other RFCs/updates of RFC5545 #589
• https://www.rfc-editor.org/rfc/rfc7529.html