[Orgmode] HTML / Site export: syntax to assign a class to a div

[Ben]

Dear orgmode users,

I'm slowly (but firmly) getting my workflows and documents fitting in
orgmode. That's great. The agenda and notes-taking part is done and
I'm now migrating a few websites into org as well.
I've a pretty simple question which puzzles me though pretty
intensely. I've crawled the mailing list archives in vain -- the topic
is sometimes mentioned without an apparent solution.

I would very simply like to assign to an orgmode document section (or
subsection) a parameter which will be translated as a class attribute
in the corresponding div in the HTML output.

Example:

* Important section
** Serious Stuff
blah
** More serious Stuff
* Note
  :CLASS: rightbox
a silly comment
* Conclusion

orgmode would then name the div sections as usual, I would like to get
for the 'Note' section another attribute which would be
class="rightbox".

I've tried the #+HTML hacks, the html_attr, the drawers and even the
#+anchor tag. In vain. I'm sure I'm missing something obvious.
Any help would be really really much appreciated!

 -- Ben