If you attempt to set desiredKeys on a notificationInfo for the new iOS 10 CKRecordZoneSubscription class, saving results in the runtime error:
<CKError 0x17424b610: "Invalid Arguments" (12/2006); server message = "cannot add additionalFields to this subscription type"; uuid = 4E08C616-97AA-4E9A-B584-B7972B1CD99B; container ID = "iCloud.com.x">
Which makes sense given the notification is about a zone changing and not a record, however one might assume it can send the record that was responsible for the change but looking to CKRecordZoneNotification shows no record properties are available. It’s always kind of disappointing to see subclassing not working out, i.e. where the subclass is denied features of the parent, it can sometimes point to bad class design however in this case Apple could have handled it better either by client side validation or at least a note in the header. It’s extra disappointing given in iOS 10 they refactored from flat CKSubscription inits for the different subscription types (which did have their own limitations, e.g. initWithZoneID only allowed zero for options) to subclasses. I hope they’ve thought this new design through because if it is refactored again it could be a real headache for framework backwards compatibility.