XmRepTypeAddReverse(3) on Linux
The text b3b6b1db4b43, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A representation type manager function that installs the reverse converter for a previously registered representation type "XmRepTypeAddReverse" "representation type manager functions" "XmRepTypeAddReverse"