XmPanedGetPanes(3) on Linux
The text f3135dc70b03, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A Paned function that returns the number of panes in the paned widget "XmPanedGetPanes" "Paned functions" "XmPanedGetPanes"