I think there may be an inconsistency in section 4.1.1 of caldav-schedulingchanges.txt:

   Description:  This property SHOULD be defined on all scheduling
      messages that have been automatically processed by the server.  If
      present, it contains a single CS:calendar-changes XML element.

   Definition:

       <!ELEMENT schedule-changes
                 (dtstamp, action) >

       <!ELEMENT dtstamp CDATA>
       <!-- Date-time value in UTC -->

       <!ELEMENT action (create|update|cancel|reply)>
       <!-- Type of change that occurred -->

       <!ELEMENT create EMPTY>

All other references are to a schedule-changes XML element...?

Regards,

Mark