I was developing a custom web control that I planned on consuming in a WebPart, and I had some control properties that required a reference to an image. So I had:
in my property decorations.
Well, using the ImageUrlEditor class in order to prompt a UI for selecting an image requires a reference to System.Web.UI.Design. I add my using construct, but low and behold compilation errors are flying because I am missing a reference. A reference to what? What the? I have the System.Web assembly referenced!
One would think that Microsoft would have put System.Web.UI.Design in, ohhhh, I don’t know, the System.Web assembly reference? That reference hierarchy sorta makes sense to me.
But, instead it is System.Design.