Question about NSSplitViewController - how do I create NSSplitViewItem?


I am reading through the NSSplitViewController documentation. I just want to understand all the bells and whistles available in this view. I ran into a stumbling block pretty quickly.

From the NSSplitViewController class reference at
I understand that it has a property that is an array of objects oftype NSSplitViewItem. It also has methods to insert and remove NSSplitViewItem objects.
However, there is no documentation for NSSplitViewItem. How do I create such an object?
I saw one example online:

let svi = NSSplitViewItem(viewController: vc) where vc is of type NSViewController

But found no Apple documentation at all. It almost seems like Apple wants developers not to programmatically add/remove NSSplitViewItem.
I am not sure if the above method is future proof - given there is no official documentation it could be using something private to AppKit and break in the future.

It seems strange that the documentation for NSSplitViewController talks about NSSplitViewItem but there is 0 documentation on NSSplitViewItem!!