As part of .NET Framework version 3.0, Microsoft released Windows Presentation Foundation (WPF), which offers a new way of creating UIs for applications. Silverlight uses a subset of the full WPF and .NET Framework. You will find some classes and methods unavailable, and anything with the SecurityCritical attribute cannot be used.
Why not use the full WPF and .NET Framework?
Silverlight is a browser plug-in, so it needs to be small.
Some WPF functionality might present a security risk when run in the browser.
Not all WPF functions are cross-platform.
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