What Microsoft UI technology was used to create Zune Media player (marketplace software, not device os)?

UI looks like it could me made with silverlight, but it's not 开发者_高级运维a web app.

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I thought it was WPF too at first, but it appears Microsoft used to a custom language called UIX (related to media center) to make it.

http://www.istartedsomething.com/20071116/microsoft-iris-uix-framework-zune/