I was trying to play with MardownSharp in a Windows 8 app. But I'm getting errors in the Mardown.cs file. It doesn't have System.Configuration and RegexOptions.Compiled.

I was trying to play with MardownSharp in a Windows 8 app. But I'm getting errors in the Mardown.cs file. It doesn't have System.Configuration and RegexOptions.Compiled.

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You have two issues here.
System.Configuration is not one of the .NET namespaces available for Windows Store applications. The good news is that it seems to be used only in one of the overloaded constructors of the Markdown class:
Comment out that constructor (and the using statement). You could rewrite that constructor to make use of app local storage which would allow analogous functionality to a config file but not with quite the same implementation. I suspect you may not be using that overload anyway
With those modifications I was able to at least compile the code, I didn't take it further.