Below is the standard SE Help Center text for why answers may be deleted:
Answers that do not fundamentally answer the question may be removed. This includes answers that are:
- commentary on the question or other answers
- asking another, different question
- “thanks!” or “me too!” responses
- exact duplicates of other answers
- barely more than a link to an external site
- not even a partial answer to the actual question
Sadly, our Help Center entry on this subject is not one of the editable ones. This is an issue, because (based on flags and user deletion votes), we are also deleting answers for having insufficient sourcing.
I asked the collective minds in the teacher's lounge, and was told that's OK, as long as its a well-established site policy. So we need to establish what site policy is in this matter.