The attribute name for a designer region is _designerRegion. The DesignerRegionAttributeName field is used to identify regions within the design-time HTML markup for the control designer.
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.