I was answering the question someone asked about the jib, but yes, the mainsail is the same concept.

Luffing is not backing. The rule is specific about backing the sail. There are some clarifications on the ISAF site, umpire calls and such, that might help. I didn't post the links, because some of them appear to be out-dated, but I think the concepts are valid.

Seems to me, if you're moving in reverse, as long as you're not backing the sail, you are ROW. Not sure how useful this is in practice, of course.

EDIT: What if you pull the main to windward? I suppose you could move backwards that way (if you push it out/forward far enough, such as in light air)? I'm waiting to hear back from a local judge who might be able to better help answer this.

Mike