X-Debbugs-Cc: Spencer Baugh <sbaugh@janestreet.com>
Tags: patch

Following the request and discussion about using S-<down-mouse-1> in
https://lists.gnu.org/archive/html/emacs-devel/2025-03/msg00161.html
here is the finished patch that implements all expected features.
The patch below is shorter than the initial experimental patch,
but still correctly supports all cases: