onHover
Hide the window toolbar in full screen mode by default. It will reveal itself when the mouse moves into the area occupied by the menu bar.
Declaration
static let onHover: WindowToolbarFullScreenVisibilityDiscussion
This has no effect if the toolbar is completely hidden, i.e. setting the visibility to hidden for windowToolbar placements using toolbarVisibility(_:for:) will cause the toolbar to remain completely hidden, even in full screen.