ImmDoc .NET is a command-line utility for generating HTML documentation from a set of .NET assemblies and XML files created by the compiler. It's developed in C#.
If user assembly has a type defined in System or Microsoft namespace, the link will point to the user type.
Type name is not checked for validity, it's blindly converted to a link as long as it matches the regex (i.e. System.Foo.Bar will create a link to a non-existing MSDN page).
MSDN links get additional target="_top" attribute, so they aren't opened inside the frame.
Unresolved types in System and Microsoft namespaces will generate MSDN links, i.e.: System.AppDomain -> http://msdn.microsoft.com/library/system.appdomain.aspx