XmDataFieldSetAddMode(3) on Linux
The text 2c1b4c16f3a5, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A DataField function that sets the state of Add mode "XmDataFieldSetAddMode" "DataField functions" "XmDataFieldSetAddMode"