I have a class that contains a certain kind of XML document. The input
file is *not* an XmlDocument, but when loaded, I want it to work like
the XmlDocument class, like:

MyDocument doc = new MyDocument();
doc.Load("input.txt");   // doc is now an XmlDocument
// Query or modify the XmlDocument as usual
doc.Save("output.xml");  // doc saved using XmlDocument.Save();

That is, the input file is not XML, and the Load() method is obviously
not the same, but otherwise the MyDocument class is a copy of
XmlDocument. Can someone please show me what the MyDocument class shall
look like to inherit from XmlDocument? I never did anything like that
before. Not that I don't want to *extend* XmlDocument with my own Load()
method. I want to *replace* all Load() methods with my own.

Gustaf