Recently, a user has asked a question whose answer he pointed out in a comment. One of the moderators voiced his opinion that "[i]t is fine to post interesting material even if you know the answer. The conventional way to do so is to answer your own question with an (elaborate) take (instead of posting a links to some document, which may break)." Is this official policy? What do others think?
It is official policy (as stated in the FAQ of every Stack Exchange site) that
It’s also OK to ask and answer your own question.
If you've done some research, thinking or experimentation to solve a problem, and there is a Stack Exchange site where you could have formulated your problem as a question, then you're encouraged to ask the question, and contribute your work in the form of an answer. This allows everyone to benefit from your work. It may also allow you to receive better or complementary answers. Everybody wins.