The particular rule is "What you can and cannot do after receiving answers." As I understand it, when we see someone edit code after receiving an answer, we should revert the edit and post a comment linking to that Meta answer. I did that on this question, and the asker has since added at least one more edit.
Should I revert again? Vote to close? Something else?
In this particular case, I flagged for moderator attention. Is that what I should always do?