Assembly: System.Design (in system.design.dll)
There is no developer advantage to creating your own designer derived from UserControlDesigner. To enhance the design-time experience for a custom control, derive your control from CompositeControl and your designer from CompositeControlDesigner. In that case, you would not use an .ascx file for your ASP.NET markup.
Windows 98, Windows 2000 SP4, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.