Inserts the given element into the set.
- iOS 8.0+
- macOS 10.10+
- tvOS 9.0+
- watchOS 2.0+
- Xcode 8.3+
The intersection of
[new and the set if the intersection was nonempty; otherwise,
new is not contained in the set but subsumes current members of the set, the subsumed members are returned.