I'm going to implement some custom Delta operations, I'd appreciate
some explanations on the expectations of the API.
I got puzzled about the method
it doesn't seem to be ever invoked, but still some Operation
implementations collect information to properly handle an eventual
rollback request (such as ClearOperation).
In case it's not needed, can we remove the method and all unneded
logic in each operation?
In case it's needed, it looks like the existing operation
implementations are not able to honor a rollback invocation after
being marshalled & ummarshalled, as most needed information is not
externalized; could anybody spend two words on it?