Am I stupid? How do I get to use XAML2009 features

Question

I've been reading a little about teh new features available through XAML2009. How do I get to use them in VS2010 (.net 4.0)?

Specifically, I want to use x:Arguments and want to know which namespace I need to include (if any).

I've read this from the documentation (below), but I can't figure how to get round it? Should I just not use thie new features?

In WPF, you can use XAML 2009 features, but only for XAML that is not WPF markup-compiled. Markup-compiled XAML and the BAML form of XAML do not currently support the XAML 2009 language keywords and features.

Or, like I say, Maybe I am just stupid.

Pete