Anyway, I have looked at your technique to log ns_return and maybe I will come up with something to reduce some passages.
I've set up a wiki page [1] for the pages I've fixed (and checked) so far to avoid duplication of work. please update this page as well (also, everybody else is invited to help). I found as well several public pages which needed some fixing.
-g
[1] https://openacs.org/xowiki/oacs-5-9-html-validity