the use of (.*) and \1 to preserve everything between tags is a useful trick
but beware of using it between <div and </div> - that seems to go horribly wrong
( in v4.3 old style regex anyway).
I have struggled to find a way to fix up books that use thousands of <div> tag pairs, one set per paragraph, and to replace with <p?> tag pairs i.e.
find <Div class =..>"every single paragraph"</div>
replace with <p> tags instead of <div> tags