I was clarifying and correcting frostschutz post, it was not aimed at your post. It looked like you might be asking about trying something in 2.0 since you were asking about Sigil. Sigil does not support 3.0. Our wiki talks about
ePub 3 and currently is weak on Javascript but have plenty of offsite links that may help. Once you figure it out please update our wiki.
I have believe that crossword puzzle should work since javascript is supported although it may be difficult to find a good reader.
I am not just posting to bump up the thread. This is a discussion group, not Ask and answer.com
Dale