Update an existing calendar event. Only the supplied fields change; omitted fields keep their current values. The change is written to Google immediately and attendees are notified of it, so confirm details with the user first. Get the eventId from ListCalendarEvents. scope picks how much of a recurring series changes and is always required: “this_event” edits one occurrence (pass the occurrence’s recurrenceId from ListCalendarEvents) and leaves the rest of the series alone; “all” edits the series itself — with time that MOVES EVERY OCCURRENCE, so never use “all” to reschedule a single occurrence. Non-recurring events use “all”. There is no this-and-following update: end the series with DeleteCalendarEvent’s “this_and_following” and create a new event instead. Passing attendees replaces the full attendee list — include everyone who should remain, not just additions. An empty string for description or location clears it. Fails on events from calendars the user cannot edit. rsvp sets the user’s own response to an invitation and is independent of the field edits — it can be the only thing this call changes. It applies at the same scope as the rest of the call, and only works on events the user is actually an attendee of.