The organizer of the event. If the organizer is also an attendee, this is indicated with a separate entry in attendees with the organizer field set to True. To change the organizer, use the move operation. Read-only, except when importing an event.
Source from which the event was created. For example, a web page, an email message or any document identifiable by an URL with HTTP or HTTPS scheme. Can only be seen or modified by the creator of the event.