On May 9, 2022, at 10:38, Eli Zaretskii <eliz@gnu.org> wrote:
Emacs doesn't discover composition rules. The composition rules are
part of the Emacs code, see the various *.el files in lisp/language/
directory. Some of these composition rules are derived automatically
from character properties, see composite.el and characters.el (which
cannot happen without Emacs knowing up-front about the properties).