A comment was left on a question I asked that stated that it's not okay to ask for links to documentation:
Unfortunately, we're not here to provide links to documentation (asking that is actually specifically off-topic).
I completely understand how a question about locating documentation, rather than just using a search engine, can be against the rules, but I don't think that applies to my question. If you read how I originally worded the question, you can see that I did ask for documentation, however, I don't think it was inappropriate to do so since that wasn't the entire point to my question.
After asking the comment poster why asking for documentation was against the rules, he/she referenced https://superuser.com/help/on-topic and replied:
It counts as a "learning material recommendation."
Maybe I'm interpreting that phrase incorrectly, but I believe that it is referring to subjective questions that ask for "recommendations" (i.e. Where can I find a good book on browser caching? or Can you recommend a site where I can learn about browser caching?)
To be fair, asking for users to support their answers with documentation if available may be unnecessary since the guidelines encourage "links to external sources." However, should a question be considered invalid just because the user asks if documentation exists and, if so, to include a link to it?