XmRegisterSegmentEncoding(3) on Linux
The text 15370e56d45f, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A compound string function that registers a compound text encoding format for a specified font list element tag "XmRegisterSegment\%Encoding" "compound string functions" "XmRegisterSegment\%Encoding"