XmCommandAppendValue(3) on Linux
The text 997f86ec60fa, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A Command function that appends the passed XmString to the end of the string displayed in the command area of the widget "XmCommandAppendValue" "Command functions" "XmCommandAppendValue"