splitView(_:shouldHideDividerAt:)
Allows the split view controller to determine whether the user can drag a divider or adjust it off the edge of the split view.
Declaration
@MainActor func splitView(_ splitView: NSSplitView, shouldHideDividerAt dividerIndex: Int) -> BoolDiscussion
By default, NSSplitViewController hides the first and last dividers if their outer neighbor is in a collapsed state.