XmStringInitContext(3) on Linux
The text e3984b8e203f, 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 creates a data structure for scanning an XmString component by component "XmStringInitContext" "compound string functions" "XmStringInitContext"