I've seen this topic come up offhand several times now, so it seems worth rule-lawyering into. With that in mind...


In a recent question,
Push pull transformer winding

the OP asked (in part):

"I'm also asking for some good documents for transformer windings if anybody knows"

which begat the answer (in part):

"off-topic" response

(quote truncated for brevity)

with comments (at time of recording),

comments to answer

My acute confusion being made evident by the satirical tone, which it seems failed to land. Noted!

I have seen documents, ranging from websites, to academic papers, books, and software, all suggested on this site from time to time. Several renowned authors even contribute here, with their papers and books never far from view. None of them have been edited or removed for inappropriate promotion, and few questions are being closed (and of them, mostly because they are blatantly asking).

Obviously, I haven't done, and can't do, an extensive search of open and closed topics, edited and deleted answers, etc.; moderators may have more insight here.

At the very least, the prohibition seems to be very slight, or even, more of a recommendation than a strict rule.

Underlying this observation, of course, is the assumption that all the content on this site is actively and willfully curated to the moderators' and admins' approval. This is, I'm quite sure, an extraordinarily faulty assumption -- but it is nonetheless one I am able to make, as the content is simply whatever the content is, and whether something has escaped any degree of review at all (or has been reviewed but was approved erroneously), or been subjected to strict scrutiny, there is no way to tell. A random viewer, brought here by search engine, would reasonably expect similar.

At best, the fact that users have not identified these cases as a problem, suggests that mods/admins do not desire a stricter regulation of it. Rules could be made more specific; placed more prominently; existing topics could be searched for keywords and ferreted out. That these actions have not been taken, gives some support to the assumption.


There are two basic ways to interpret law: categorical and specific. Existing law dictates: book recommendations are off-topic.

(I use "law" informally here, meaning the known, written rules of the land, not that there is a necessary cost or punishment associated with their violation; I suppose "norm" is the word I should be using. But, to the extent that editing to remove offending content counts as a violation, or to the extent it might escalate to a platform ban (without extenuating reasons), it seems somewhat applicable.)

Categorically speaking, one would interpret this [the basic statement] to mean: Any and all book recommendations are strictly prohibited.

This seems contradicted by the abundance of topics which do.

There is an alternative interpretation: the moderator team is either powerless to stem the tide, or capricious in their will to do so. I have no interest in such an extreme interpretation, but the mods/admins are likely aware of the existence of this interpretation, and therefore seek to avoid actions which would paint such an unfavorable picture. (In contrast, I would take this as more reason to assume good faith.)

The specific reading, in contrast, asks to dig deeper. A category might be recognized, but it matters which items within that category are prohibited, and why.

So, let's dig in. Assuming we accept the answers as fact; and, prioritizing moderator opinions as presumably more important --

Stack exchange has evolved significantly from what it was 7 years ago when the question you referenced was posted. The recommendations on what is on topic have changed.

The old questions are still kept around because they are still useful

Voltage Spike

This answer links the on-topic help, of which the most applicable item is "a shopping or buying recommendation" (which is also highlighted in the background concern above). This is understandable: insipid promotion, or outright spamming, would pollute this site, making it less useful, and less interesting to participate in.

Additionally, whole books are a lot of material to review, and likely few users have read any given book, so there is very little review that is likely to take place; discouraging (but not outright prohibiting) book recommendations, might cost some answers good supporting material. (Mind, supporting as in, not direct information -- if quoting from a book, one must of course cite that as the primary source; and this is, I would say, a good way to provide book recommendations; it is the academic standard, after all.)

What this answer does not discourage, is citations in general, nor free resources -- the answer discusses the rule very little, and the rule is very specific: "shopping" or "buying". If there's no monetary transaction, there's no violation. We would likely include pirated books or articles as well (no cost to the end user, but obvious legal issues). Still, I see no possible way this could prohibit freely published articles for example, or informational websites.

The top upvoted answer at this time,

I can offer some reasons why from the older sister-site Stack Overflow.

Book recommendations were once on-topic. This spawned a whole lot of very low quality "recommendation" threads, where anyone could recommend anything. It was completely subjective and there were no prerequisites for recommending a book - some people even recommended books they had not read themselves. So essentially you ended up with a list of everything ever written about the topic, both good and bad.


This gives explanation why; and it seems I have correctly anticipated the reasoning behind this decision.

We can extract a rule from these, then:

Asking for book recommendations is, at the very least, discouraged, and most likely results in a question being closed. (This is also easy to implement, as users can be told to find and close them, a relatively simple pattern-matching task.)

Providing book recommendations in an answer, is acceptable, provided:

  • It's not the predominant content of the answer (e.g. a book rec. list)
  • It's used to support ones' point, provide facts, etc.; preferably quoted in relevant sections, and cited clearly
  • The author has read the book, and considers it a valuable resource, in good faith
  • The book is easily reviewable in some way (most likely, short and freely available), so that voters, commentators, or (would-be) editors can weigh in as desired.

Where some weighted combination is taken over these options; not that any one, nor all of them, need be passed.

This is my understanding, explains existing material very well, and is supported by my own posting practice, which has not had citations questioned, at least that I recall offhand (forgive me if I don't have categorical offhand knowledge of thousands of posts!).

The meta question even offers a recommendation as example: the classic Horowitz and Hill. Books well renowned in the wider professional or academic communities, have a better chance of satisfying the last point despite their length.

As for my own motivations here, I have no interest in questioning the book recommendation policy; I suspect my above interpretation of it is accurate enough (corrections welcome).

I do, however, have a strong motivation to improve the quality of content on this site. I suspect that many contributors have gathered the wrong impression and don't provide citations when they should, or as often as they should. As a result, many (most? nearly all, even?) answers reduce to dreaded opinion -- which is ostensibly off-topic here (but that's a matter for another question, perhaps).

Anyway, returning to the matter at hand:


I wish to settle this particular matter:

The OP asked for "some good documents" on a topic. An answer shot back "no, that's shopping".

  • Are publicly listed websites "shopping"?
  • Are free academic papers, white papers, application notes, etc. "shopping"?
  • Are books (printed, e-book, PDF, etc.; in copyright or not, ) "shopping"?
  • Are any other kinds of documents (printed or mixed media, audio, uh... other senses?) "shopping"?

If so, which ones, when, and why?

Additionally, without befalling any particular site rule as such -- under which circumstances might such an element, of a question or answer, be discouraged?

  • It should be on topic, related to the question, and motivating the answer, of course.
  • What else?

I have also seen other commentators actively discouraging research or citations in general. The above should clear up those matters, but any comments further distinguishing those circumstances from the above would also be welcome.


2 Answers 2


I agree, this question looks like a design question to me. I don't think it should be closed. Closure discussion should not take place in an answer. The OP is asking about designing a transformer.

As far as shopping questions go, anything asking for a resource is off topic. This comes from Jeff Atwood. There are many questions that can be modified and help, not discouragement should be given to the user (especially new users). SE is a place for friendly behavior, if you come here to discourage other people (per the CoC) then you should find another place on the internet to do this, SE is not the place for this. EE.SE is a place to ask questions and is a repository for good questions and answers. The whole site is built to facilitate this.

  • \$\begingroup\$ Could you source this Atwood quote? And, by "as far as shopping", does that mean any purchased resource, or is that in general, any resource period? As you might understand from my lengthy post, I was hoping for unambiguous answers, thanks! \$\endgroup\$ Sep 27, 2023 at 16:57
  • \$\begingroup\$ Just read the article every time the shopping link comes up when a question is closed. \$\endgroup\$
    – Voltage Spike Mod
    Sep 27, 2023 at 17:10
  • \$\begingroup\$ I think the root of the problem is that other sites like SO just call it "resource recommendations" and use the same close reason for everything from code/library/book/tool etc recommendations. Whereas here at EE the "shopping" close reason was supposedly only meant to cover "where can I buy"/"which brand is cheapest" etc. But it should also have included other forms of recommendations too. \$\endgroup\$
    – Lundin
    Sep 29, 2023 at 11:28
  • \$\begingroup\$ @Lundin As I understand it the shopping question does cover all forms of recommendation here and questions are usually closed as such, unless the user (especially new users) can be helped to understand how they need to change their question and the question can be edited. \$\endgroup\$
    – Voltage Spike Mod
    Sep 29, 2023 at 15:28

There's no such thing as an off-topic answer, at least in any context involving closing or removing an answer (excepting, of course, violations of "be nice" and clear site abuse like spam).

In that sense, there isn't much real point in trying to assert more rules that more people might or might not know. If it makes sense to mention a book, web site, or other resource in an answer, then it makes sense, and the answerer is free to do so.

It doesn't make a difference whether the answerer has read the book or used the resource. We have a direct mechanism to deal with answers that lack credibility -- the down vote.

In principle, the last thing we want to do is deter somebody with a valid contribution from contributing it.

  • 2
    \$\begingroup\$ Scott - Hi, Broadly agreed - we don't want to deter valid contributions. However just to be clear, it is possible to have off-topic answers leading to their removal - please see here from our Help. For example, something posted as an answer to question X which doesn't answer question X is eligible for deletion. We regularly get (correct) flags for this. A typical example, but not the only type, is a new user asking a new question as an answer on an old topic i.e. using this site like a forum. I sometimes delete several per day. \$\endgroup\$
    – SamGibson Mod
    Sep 27, 2023 at 17:27
  • \$\begingroup\$ @SamGibson -- sure. I throw those all in as "site abuse". The flag is usually "Not an answer" for those, after all. \$\endgroup\$ Sep 27, 2023 at 17:52
  • \$\begingroup\$ "There's no such thing as an off-topic answer" Of course there is. If someone asks a question about Kirchhoff's Laws and I give an answer about pony riding, by answer should get deleted as being off-topic. Or if someone asks a question about Kirchhoff's Laws and I give an answer about VHDL, then my answer is on-topic for the site but off-topic for the question asked - and should deleted since it is just as irrelevant as the pony riding answer was. \$\endgroup\$
    – Lundin
    Sep 29, 2023 at 11:32
  • \$\begingroup\$ @Lundin, yes, if the downvote procedure mentioned in my answer is employed, then answers can be deleted. The process starts with more downvotes than upvotes, \$\endgroup\$ Sep 29, 2023 at 11:47

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