Stack exchange frowns on answers containing only a link, even if it's to relevant information, because:
- It requires extra effort from the reader
- It is vulnerable to link rot
- The stated goal of Stack Exchange is to host content, not just link to it
A common approach to these answers is to leave a comment asking a user to add some more information and/or quote an excerpt from the link target.
However, what should we do if the author does not follow through?
On the one hand, the answer might still be very useful for future visitors who do follow the link. On the other hand are the numbered items above.
This has been discussed on meta stackoverflow - and there are basically two highly-upvoted answers there, one encouraging a downvote, the other encouraging deletion or improvement (both recommend leaving comments first). Which way should we go?
Notice that there is no appropriate post annotation for this (like there is for unsourced answers)