RFC 5545, "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", September 2009Source of RFC: calsify (app)
Errata ID: 6316
Publication Format(s) : TEXT
Reported By: Ken Murchison
Date Reported: 2020-10-22
Section 188.8.131.52 says:
Value Type: The default value type for this property is DATE-TIME. The value type can be set to DATE.
It should say:
Value Type: The default value type for this property is DATE-TIME. The value type can be set to DATE. This property MUST have the same value type as the "DTSTART" property contained within the recurring component. Furthermore, this property MUST be specified as a date with local time if and only if the "DTSTART" property contained within the recurring component is specified as a date with local time.
EXDATE excludes a specific instance of a recurring event and therefore should have the same value type as DTSTART. This is analogous to RECURRENCE-ID which overrides a specific instance and has the same value type as DTSTART.
I will note however that there is iCalendar data in the wild with DTSTART;VALUE=DATE-TIME and EXDATE;VALUE=DATE. If this errata is rejected as incorrect, then a new errata should be opened with additional text describing how EXDATE;VALUE=DATE is supposed to be handled when DTSTART;VALUE=DATE-TIME. For instance, does EXDATE;VALUE=DATE exclude ALL instances of a FREQ=HOURLY recurrence on the given day?