I think that we are going to get a lot of questions that ask about something in between a puzzle and a game, about the rules. I'm sure there are many rules questions that would be better fit for a games related StackExchange, but there will be some that apply specifically to puzzles. Do we want to answer these, migrate them, or just close them as "RTFM!"?
Questions about rule clarifications and judgements, and similar meta questions about the rules are unambiguously on-topic.
Questions asking for a complete set of rules are trickier. On the one hand, we don't want to just be a repository for the rules of all puzzles; on the other, not all puzzles are going to have clear Ms to RTF. I think we should err on the side of acceptance, and if it gets to be a problem we can revisit the issue then.