Great news. [MS] finally released a part of .NET Framework Source Code for debugging purposes. A move that didn't even seem possible a year or so ago. Anyway, these are the assemblies available for inspection. If I understand properly more will follow.
- WPF (UIAutomation*.dll, System.Windows.DLL, System.Printing.DLL, System.Speech.DLL, WindowsBase.DLL, WindowsFormsIntegration.DLL, Presentation*.dll, some others)
Read more about how to enable symbol/source code loading in Shawn Burke's post and don't forget to install this Visual Studio 2008 QFE (otherwise you'll be bugged with license agreement windows all the time).
Read also license agreement clarification (from Scott Guthrie's post) about possible concerns:
The .NET Framework source is being released under a read-only reference license. When we announced that we were releasing the source back in October, some people had concerns about the potential impact of their viewing the source. To help clarify and address these concerns, we made a small change to the license to specifically call out that the license does not apply to users developing software for a non-Windows platform that has “the same or substantially the same features or functionality” as the .NET Framework. If the software you are developing is for Windows platforms, you can look at the code, even if that software has "the same or substantially the same features or functionality" as the .NET Framework.