XmTextGetInsertionPosition(3) on Linux
The text f280832d6389, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A Text function that accesses the position of the insert cursor "XmTextGetInsertionPosition" "Text functions" "XmTextGetInsertionPosition"