I know the differences between mathoverflow and math-stack but I have been wondering:

Are there legitimate mathematical questions that would not get answered at math-stack because there is no expertise around and yet would be considered trivial (not research level worthy for mathoverflow?)

I agree that the fact that a question that is not answered at math-stack should not be "upgraded" to mathoverflow but is there some other site that covers a middle ground? Is there a place one can ask clarification questions about material covered in PhD math classes?

If you allow me to illustrate, I posted this question https://math.stackexchange.com/questions/554397/effect-of-pullback-of-differential-forms-on-an-ideal that I think is perhaps too trivial for the overflow crowd but that despite a bounty about to expire is languishing at math-stack. I'm afraid there is no good site for type of questions that are appearing in my self-study. Thanks for any feedback.

readingarticles orgraduate level books." (my emphasis) In principle such a q is on-topic on MO (your q is really not in my field so I do not want to make any definite statement). In general, good graduate level q are welcome, only sloppy and/or completely standard ones are put on hold. Now, it can likely happen one thinks it is good but turns out to be 'comlpetely standard' to someone, but then this is not that big a problem. $\endgroup$in principle, there's not supposed to be anything that is "too advanced" for math.SE; that is, math.SE is supposed to welcome question atalllevels. In practice, it is likely that advanced questions will receive attention from an audience more likely to answer them in mathoverflow than in math.SE (because of the composition of the readerships of both groups), but that is a different question from whether it would be on-topic in math.SE. (cont) $\endgroup$andwas not getting any answers in math.SE, then it would be suggested that it be crossposted to mathoverflow (I don't know if migration is now possible that the two sites are on the same platform). Again, this would be different from saying it was off-topic or inappropriate for math.SE. My general impression is that the set of questions appropriate for mathoverflow are a proper subset of those that are appropriate for math.SE; again, this is different from whether a question is more likely to get useful answers here or there. $\endgroup$