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5.1.1. Updating, transporting and maintaining start, and and duration

  • For all components the calculated or specified start must be at or before the end.

  • When a system updates or stores a calendar component it MUST retain the relationship of start, end and duration. Applications MUST NOT without good cause, change a start and end pair into a start and duration nor the reverse. Semantically they are not equivalent when DST transitions occur during the time of the event.

  • For interoperability, iCalendar based systems SHOULD avoid the use of weekly durations and XML based systems SHOULD avoid the use of yearly durations.