i just realized that there is still a big problem when it comes to validation of xul-documents in Visual Studio.
When you localize your xul-file using a DTD, Visual Studio won't accept it because of the chrome-URI.
<!DOCTYPE window SYSTEM "chrome://myApp/locale/main.dtd">
will give the following error: "The URI prefix is not recognized"
Even if we could register the prefix somehow, Visual Studio has no way to know about the entities, as it doesn't know how the chrome protocol works.
i know we can't solve this via the schema, but i thought i'll ask you, maybe you have an idea.