mtext_case_compare(3m17n) on Linux
The text 81d007e8e416, as Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie), Debian 7 (Wheezy) shipped it.
Compare specified regions of two M-texts ignoring cases.