Registers an observer to receive key value observer notifications for the specified key-path relative to the objects at the indexes.
- iOS 2.0+
- macOS 10.3+
- tvOS 9.0+
- watchOS 2.0+
The index set.
The key path, relative to the array, to be observed.
The options to be included in the notification.
The context passed to the notifications.
options determine what is included in the notifications, and the
context is passed in the notifications.
This is not merely a convenience method; invoking this method is potentially much faster than repeatedly invoking