Position the browser window so that the blue part of this page extends behind the system taskbar.
Use your mouse to drag the orange box over a part of the taskbar that overlays the blue part of this page.
If supported by the platform, the mouse cursor should not show the browser's custom "copy" cursor, and should instead show the system's expected cursor for dropping on that part of the taskbar.
Release the drag. Fail if the text on this page changes.
Reload and repeat this test for:
Where the blue part of this page extends under an always-on-top window (eg. the Windows Task Manager).
Where the blue part of this page extends under an always-on-top notification (eg. a system tray info balloon).