XmAddTabGroup(3) on Linux
The text 08a4f410ed45, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A function that adds a manager or a primitive widget to the list of tab groups "XmAddTabGroup" "VendorShell functions" "XmAddTabGroup" "protocols"