To produce XML coded metadata, Microsoft have a utility XSD.EXE which comes with C#. This produces an XML scema. It can also work in the opposite direction and create a C# class definition from a scema.
The C# compiler will process documentation comments in your code to an XML file. Processing the XML file to create documentation is a detail that needs to be implemented at your site.
Tags are processed on code constructs such as types and type members.
Note Tags are not processed on namespaces.
The compiler will process any tag that is valid XML. The following tags provide commonly used functionality in user documentation: