The bulk of the proposal is (currently) in a PDF; see attached file. The proposal comes from the Google teams working with the existing Event markup, and has been checked by the other schema.org partners prior to publication. See PDF for full details of the proposal.
A slightly revised proposal was updated in May 2013, and includes improvements for the repeating events model.
Event schema.org proposal
(todo: check these, are they acccurate for the May 2013 update?)
- Proposes 3 new properties of Event: eventStatus, previousStartDate, previousEndDate to support canceled or rescheduled events.
- Adds eventCategory to support categorised events.
- Supports recurring events by making startDate and endDate repeated.
- Encourages use of existing 'url' property (of Thing) to link to associated Web pages.
See also: [ActivityActions], where the Action type shares some Event-like structures.
Note from WebSchemas/Singularity a property re-naming (in progress, Mar 2012):