If someone answers my question and I want to generalize it, how should I do it? Is it ok to gradually extend my question as answers improve? An answer to a question I wanted to ask may show me that I really wanted something else, whence asking just what I need is not always possible. (This is especially true of research related questions, which should be the ones we want here anyway.) Is there a good principle for deciding whether to extend an old question or to make a new one?

From the other perspective, if someone keeps extending their question, should I extend my answer or give several answers?

Something of this kind happened with <a href="http://mathoverflow.net/questions/176720/bmo-spaces-on-the-torus">this question</a> that I answered recently and it left me thinking.