XmClipboardCancelCopy(3) on Linux
The text fbe8e5556b9b, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A clipboard function that cancels a copy to the clipboard "XmClipboardCancelCopy" "clipboard functions" "XmClipboardCancelCopy"