ChnlStack(3) on macOS
The text 6351de644cdc, as Mac OS X 10.2.8.G5, Mac OS X 10.2.8, Mac OS X 10.2.7, Mac OS X 10.2.6, Mac OS X 10.2.5, Mac OS X 10.2.4, Mac OS X 10.2.3, Mac OS X 10.2.2, Mac OS X 10.2.1, Mac OS X 10.2, Mac OS X 10.1.5, Mac OS X 10.1.4, Mac OS X 10.1.3, Mac OS X 10.1.2, Mac OS X 10.1.1, Mac OS X 10.1, Mac OS X 10.0.4, Mac OS X 10.0 shipped it.
stack an I/O channel on top of another, and undo it