Where are the Razor assemblies?

I'm playing around with WebMatrix and I'd just like to explore some of the开发者_运维百科 razor stuff behind the scenes... but my Reflector skills (and my brain) are failing me. Does anyone know offhand what assembly I should start looking in (and/or a location for it)?

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All the assemblies are installed into Program Files as well as into the GAC. The local folder is:

C:\Program Files\Microsoft ASP.NET\ASP.NET Web Pages\v1.0\Assemblies