XmDropSiteConfigureStackingOrder(3) on Linux
The text 5c558a6eab66, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A Drag and Drop function that reorders a stack of widgets that are registered drop sites "XmDropSiteConfigureStack\%ingOrder" "Drag and Drop functions" "XmDropSiteConfigureStack\%ingOrder"