I would like to write an extensibility extension for my product that
basically is a browser to an XML front end.  I want to use the features in
Visual Studio Extensibility, but extend them  to do things like check to
make sure an Assembly.Class.Method is valid for an element value.  In other
words I have elements that take an argument of the form
'AssemblyName.ClassName.MethodName'  I want to use extensibility to verify
this is a valid reference in the XML document.

Additionally, I would like to use the GUI designer to display the objects I
create from the XML.  Would this cause any problems, I plan on using .NET
controls in the designer.  I know there are limitations on what you can put
in an extensibility package but I am not sure so I wanted to double check
with you guys.

Also I looked at the Isolation Deployment package and it requires knowledge
of C++ which I do not have.  Would I be able to write the Standard,
Professional, and Team editions in managed .NET C# code?