This parameter specifies a unique recurrence date of an event or todo. Use rid in conjunction with the mod parameter to specify a range of events and todos to be modified.
For example:
http://webcalendarserver/storecomponents.wcap ?id=b5q2o8ve2rk02nv9t6 &calid=jdoe &uid=333 &dtstart=20020301T112233Z &rid=20020331T112233 &dtend=20020301T112233 &summary=uuuu&mod=1 |
For a non-recurring event or todo, the rid is 0.