Lack of examples are disservice to the lesson. A significant problem is distinguishing the “uncommon” from the “bad”. An attempt to prevent something bad altogether can impede an uncommon, yet desirable behavior.
Consider what people today call “monkey patching”. Should this be ruled out altogether? (Rhetorical… this i not a discussion for that topic per se.) Or should it be supported explicitly, and highlighted to be readily apparent? Arguments could be made either way, and the end affect on programmers will be significantly different.
So good topic, but not so helpful post for guidance.