Ask HN: how do I fill in a 'declaration of prior inventions'

I'm about to start a new job and have to fill one of these in. I don't have any patents to write down, but I do have a number of side projects, open source contributions, and works that I've licensed to previous clients which I don't want my new employer to make a claim on. I'd like to keep my options open wrt monetizing those of my side projects which don't compete with my employer.

- How much detail should I give?

- Should I even bother with things that don't compete with my employer?

- Is this form actually worth anything in court? (It's actually a Japanese company, I've yet to find a good resource on Japanese employment law.)