What is the vertical property on NSStatusBar?

Question

I just looked at the Apple documentation for NSStatusBar, and found this curious property:

vertical Property

A Boolean value indicating whether the status bar has a vertical orientation. >(read-only)

Declaration

@property(getter=isVertical, readonly) BOOL vertical

Discussion

When the value of this property is YES, the status bar has a vertical orientation. The status bar returned by the systemStatusBar method is horizontal and has the value NO for this property.

Availability

Available in OS X v10.10 and later.

It's unclear whether this is used anywhere, because it's apparently not really used on [NSStatusBar systemStatusBar], which as far as I know is the only instance.

What is this for?