<p>The basic policy is clear enough -- don't answer in comments, answer in answers. Some SE sites are very strict and simply remove anything in comments that looks like an answer. Others run a bit looser. </p>

<p>If someone does answer in comments and you expand it into an answer, then as long as you give credit where you rely substantially on someone else's text, there's no issue as far as I can see; you're actually doing the right thing -- putting an answer on a question.</p>
