Is anyone aware of an RFC describing a ATTENDEE property parameter called "TO-ALL-PROPOSED-NEW-TIME"?
macOS 10.12.4 Calendar.app has implemented propose new time using this property:
ATTENDEE;CUTYPE=INDIVIDUAL;PARTSTAT=TENTATIVE;TO-ALL-PROPOSED-NEW-TIME="
DTSTART:20170512T060000Z;STATUS:NEEDS-ACTION;":mailto:x@y.z
but our server is unable to parse the VCALENDAR as this property parameter is unknown.