@b0rk I think I know intuitively what "top" and "bottom" mean (at least in the diff3 format), even though if someone asked me, answering would require more thought. In the process of comparing to the middle revision, I'll think things like "oh, upstream did this" without really thinking about which one is upstream.
@b0rk In this thread I keep seeing "they're flipped in rebase", but I think it's actually the rebase command that's backwards. You give merge the revision with the changes you want to bring in, but you give rebase the revision you want to add your changes to.
@b0rk I think in my intuition HEAD/top is "the thing I'm adding changes to" and bottom is "the changes I'm adding" - the branch I merged in, or the commit I cherry-picked (including in a rebase) or reverted.