The revision ID of the presentation containing this page. Can be used in
update requests to assert that the presentation revision hasn't changed
since the last read operation. Only populated if the user has edit access
to the presentation.
The format of the revision ID may change over time, so it should be treated
opaquely. A returned revision ID is only guaranteed to be valid for 24
hours after it has been returned and cannot be shared across users. If the
revision ID is unchanged between calls, then the presentation has not
changed. Conversely, a changed ID (for the same presentation and user)
usually means the presentation has been updated; however, a changed ID can
also be due to internal factors such as ID format changes.