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Although you can use the control correctly in Visual Studio 2010, the Margin property highlights as an inexistant property in Blend 4 RC. Though I'm not sure if that's an issue with the RC version (though I haven't had any problems with other controls) or the control, I'm just wondering if there's a workaround other than adding a wrapper panel around RadBook to apply the Margin so that Blend doesn't choke out on the error.