XmClipboardUndoCopy(3) on Linux
The text 19b446b1c162, 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 deletes the last item placed on the clipboard "XmClipboardUndoCopy" "clipboard functions" "XmClipboardUndoCopy"