XmTextFieldGetSelectionPosition(3) on Linux
The text ead78c0adff5, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A TextField function that accesses the position of the primary selection "XmTextFieldGetSelection\%Position" "TextField functions" "XmTextFieldGetSelection\%Position"