Thank you Nathan, this has been very helpful and I was able to successfully create the problem that I wanted. Just out of curiosity, this does not work when no checkboxes are selected because of how the checkbox object has been coded in the "PGchoicemacros.pl", macro, right?
Basically yes. I think that when nothing is marked - the answer gets handled by a "pre filter" in such a manner that AnswerHints does not receive it for processing. I did not look into it deeply enough to be certain.