XmVaCreateCascadeButton(3) on Linux
The text eaec62f64fab, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A CascadeButton widget convenience creation functions. "XmVaCreateCascadeButton" "XmVaCreateManagedCascadeButton" "creation functions"