One of the most significant features of the ASP+ programming model is the ability to create custom controls based on the ASP+ Web Forms Framework. Reusable custom controls can encapsulate common functionality and dramatically reduce the amount of code a page developer must author.
ASP+ was designed to allow developers to extend or replace the supplied controls with custom-written controls. ASP+ custom server controls can be based on the supplied intrinsic controls, which can be modified and extended, or they can be totally new creations.