XmStringNConcat(3) on Linux
The text 06e72730122c, 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 appends a specified number of bytes to a compound string "XmStringNConcat" "compound string functions" "XmStringNConcat"