XmContainerCopy(3) on Linux
The text 7f377003cda6, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
Container widget function to copy primary selection to the clipboard "XmContainerCopy" "XmContainer"