"No" is a valid answer to "is this possible?". Sometimes it can be quite useful. A recent example: [How to ban all connections to .se and .ru in the hosts.deny file](https://unix.stackexchange.com/questions/516588/how-to-ban-all-connections-to-se-and-ru-in-the-hosts-deny-file/516594#516594)

Or not?

* <https://twitter.com/srostedt/status/1132009918444318721>
* [Change format of syscall event trace output to ftrace](https://unix.stackexchange.com/questions/512503/change-format-of-syscall-event-trace-output-to-ftrace/)

EDIT: In the two links above, you can currently see a "no" answer which was deleted, and converted into a comment. But looking at [When to "Comment", and when to "Answer"?](https://unix.meta.stackexchange.com/questions/5344/when-to-comment-and-when-to-answer) , I would think it fits better as an answer, and does not fit well as a comment.

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This type of answer might be most useful when worded "It is not possible in version 42. The current features (or architecture) are exhaustively documented <here>, and none of them will let you do this."

I think there is no written rule that requires that wording. I can imagine a moderator wanting to avoid the "this answer is not useful" scoring process etc, for an inexperienced StackExchange user. But I am not convinced this is the best approach. As an example of an alternative, I saw another short, new answer today, which received a comment response "Do you have any references for this?"

In this particular case, an edit like "citation: I am the first name listed in the `MAINTAINERS` document for this code" could make the answer more useful. The author has since attempted to provide this information.

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This answer is not simply a pedantic mis-understanding of a common idiom. It would still apply when question posts are worded "I want to do X, and I need to do it using tool Y *because reason Z*". The correct answer may be "tool Y cannot do X".

The caveat here is that when you cannot tell what reason Z is, it can be unclear what the intended question is. Does the asker require answers to use tool Y, or did they just assume that tool Y would have a good way to do X? That is what we have question comments for. And ultimately, the ability to put a question on hold. I.e. if a post is not a good fit for this site's definition of a question: a post that can have a definitive answer.