make attribute replacement easy (especially for "class" attributes)

[iham]

every theming framework I know - bootstrap, foundation, tailwind - relies heavily on interchangeable classes to style UI elements.
since plone 6 uses Bootstrap 5, it would be very useful to be able to replace css classes for a theme on the fly using diazo.

diazo promises to keep you away from xsl, but all solutions I found are heavy xsl rules, copies of attribute contents, mind boggling stuff.

eg: if you have this:

<div class="class-a CLASS-B">...</div>

and want that to become this:

<div class="class-a CLASS-C">...</div>

maybe adding params to <drop>|<replace>|<merge>?

a better DX would be awesome!