Hm...  I think shr.el should render <sup>, but I don't know how.
(That's "superscript" in HTMLese, as in 34², for instance.)

Is there a way to raise part of a line?  I tried playing with

(put-text-property (point) (+ 4 (point)) 'line-height '(12 40))

but that didn't work.

And the same goes for <sub>, which does the opposite thing.

Any ideas?