Excellent question! In the early days of Stack Overflow (before there were comments!), answers regularly referenced each other. (My top-voted answer still bears the marks of that practice.) But it quickly became obvious that answers work best when they are reasonably self-contained. This is why you might occasionally see complaints about link-only answers. As you say, referencing position makes little sense when answers may be moved around by voting.
If you want to reference another answer, the usual way to do it is with a link. During the private beta, that's a little harder than normal since the
share link is removed from the interface. But when the site goes public you will be able to copy a direct link to the answer itself:
Then you can use Markdown's link syntax:
Building on [UnCleJack's answer](https://parenting.stackexchange.com/a/11828/4521)...
Depending on how much you want to add, you might be better off suggesting an edit to the answer instead. It's a judgement call, but the more you have to add, the more likely you should write a new answer.
When answering, I have two audiences in mind:
- The asker, and
- The future readers.
As a rule, the asker will be less and less important as time goes on. Many questions I've asked are no longer interesting to me, but continue to help future searchers. I try to answer starting from specifics and expanding to generalities:
In your situation, X should work well, but you might also consider Y and Z when similar problems arise.
That sort of thing.
Blogging turns out to be good preparation for answering on Stack Exchange. I sometimes pretend that the question was an email that I decided to answer publicly. Other people might be answering too, which is interesting. But my answer should stand on its own. Obviously it's critical to answer the question directly. But there's also room to address the bigger picture. Ultimately, we optimize for pearls:
Incoming questions are a universal constant, all around us in countless billions. But answers—truly brilliant, amazing, correct answers—are as rare as pearls. Thus, questions are merely the sand that produces the pearl.
So be careful not to let other answers distract you from creating timeless, complete, and expansive answers.