Not very many. It's actually a good thing if you don't assume that all of your viewers are suffering from severe dimentia that requires every intricate detail to be laboriously explained. The few people who don't get it aren't worth pleasing by sacrificing the quality of the movie with endless and unnecessary exposition. (Especially when the final product had so many serious plot-holes that really should've been explained. God only knows why there are so many inconsistencies between the trilogies, but at least now we know how the emperor turned white!!)