XmTextFieldXYToPos(3) on Linux
The text dcbbfb45c38d, 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 character position nearest an x and y position "XmTextFieldXYToPos" "TextField functions" "XmTextFieldXYToPos"