testPart(_:)
Returns the part that would be hit by a mouse-down event at aPoint (expressed in the window’s coordinate system).
Declaration
func testPart(_ point: NSPoint) -> NSScroller.PartDiscussion
See NSScroller.Part for a list of possible return values. In macOS 10.7 and later, this method no longer returns NSScroller.Part.incrementLine or NSScroller.Part.decrementLine.
Note the interpretations of NSScrollerDecrementPage and NSScrollerIncrementPage. The actual part of a scroller that causes page-by-page scrolling varies, so as a convenience these part codes refer to useful parts different from the scroll buttons.