I was checking out the Mere Mortals sample windows application and noticed a handy feature that I was curious about. Somehow upon save, validation occurs that puts a small "error" icon next to fields that failed validation (the sample shows one next to the "Region" field. When you move your cursor over the icon it displays hypertext that shows what the problem is.

I was wondering is this part of the framework, or just something that was added for the sample application?

If it is part of the framework, how can I use it in a Web application?