It appears that interrogative words are excluded from search. This might make sense in the context of SOFU, but not on English Language and Usage.
In my case, I was looking for a question on the difference between "what" and "which", but neither of the following worked:
- https://english.stackexchange.com/search?q=what
- https://english.stackexchange.com/search?q=which
- https://english.stackexchange.com/search?q=what+which
In my desperation, and I am not making this up, I tried searching for "beer" instead, and the top result was pretty much the question I was looking for:
Could you enable searching for interrogative pronouns, pretty please, or should I henceforth resort to looking for beer?