I recently asked this questions on Mathematics.SE. At the end I put this after asking for an explanation for the answers.
I don't think that it is too unreasonable to say that if I can't understand your answer, I can't accept it.
I believe that not everyone on the Stack Exchange network is an expert on the sites on which they are active on and that asking for an explanation before I could accept a piece of code or a mathematical proof is perfectly acceptable, given that I may not understand it.
I just wanted to check if that was OK to ask so that I can refer people to this post if necessary.