drop downs on C# Forum

Question

Hi i noticed something on the forums that i would like to learn how to do. When you move your mouse over the categories up on top, a layer pops up with all the other posts/categories in that area. Is a seperate database call being made to accomplish this (thats the only way i know how to do it)? but it works so fast that i don't think thats how its done? Perhaps its done with dataviews? or cached data? Any ideas? Thanks, sam.