XmVaCreateSeparatorGadget(3) on Linux
The text 9c5c88c73fdd, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A SeparatorGadget widget convenience creation functions. "XmVaCreateToggleSeparatorGadget" "XmVaCreateManagedSeparatorGadget" "creation functions" "XmVaCreateSeparatorGadget"