XmTextFieldSetMaxLength(3) on Linux
The text eea91649cae1, 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 sets the value of the current maximum allowable length of a text string entered from the keyboard "XmTextFieldSetMaxLength" "TextField functions" "XmTextFieldSetMaxLength"