XmVaCreatePanedWindow(3) on Linux
The text 369f9095297a, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A PanedWindow widget convenience creation functions. "XmVaCreateTogglePanedWindow" "XmVaCreateManagedPanedWindow" "creation functions" "XmVaCreatePanedWindow"