A key whose value is a string that provides a sync view hint.
- iOS 9.0+
- macOS 10.11+
- Mac Catalyst 13.0+Beta
- tvOS 9.0+
- watchOS 2.0+
The corresponding value is of type
CFString, and is included as part of the primary key of an item. It can be used to help distinguish Sync Views when defining their queries.