XmTextFieldPosToXY(3) on Linux
The text bf8c039106c6, 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 x and y position of a character position "XmTextFieldPosToXY" "TextField functions" "XmTextFieldPosToXY"