startingToken
An opaque token that indicates a point in history in the user’s Contacts database.
Declaration
var startingToken: Data? { get set }Discussion
Specify nil to receive a CNChangeHistoryDropEverythingEvent, followed by an add event for every contact and group in the Contacts database.
Save the currentHistoryToken from a successful fetch result in your app, then specify it here to receive changes after that point in history.