The DesignMode property returns true to indicate that the control is being used in the context of a designer. Your custom controls can use this property when design-time behavior is different than run-time behavior.
Windows 98, Windows Server 2000 SP4, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.