Around line 270 of Ox-html.el, there's CSS which gives certain code blocks in the resulting HTML a hover-over window saying what language they encode. Not all Babel-supported languages appear however: is there any reason for this? (E.g. perl is hard-coded but no python)
I suppose one could pull all the sources from the #+BEGIN_SRC XYZ blocks and generate this on demand, using a lookup table for known languages and a basic capitalization scheme for unknown languages. I'm not much of an elisp user, but would be happy to try my hand at a patch if this would be of interest. Michael
