Indicates whether a scheduling object resource has had a "consequential" change made to it.
opaque-tag (defined in Section 3.11 of [RFC2616])
This property MUST be protected, as only the server can update the value.
COPY/MOVE behavior: This property value is determined by the server and MAY be different from the value on the source resource.
The CALDAV scheduling object resources. This property is described in Section 3.2.10.