Adding multiple namespaces in an XML file

Hi

I'm using a class which extends  %XML.Adaptor adaptor and I want to create an XML file with multiple namespaces, like the following:

<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
</soap>

However, I don't see how to do this with the code I have. So far, I have

 Class GMMHTIE.Docman.Messages.Request.RequestWrapper Extends (%Persistent, %XML.Adaptor)
{
 Parameter XMLNAME = "soap:Envelope";
 Parameter NAMESPACE = "http://www.w3.org/2001/XMLSchema-instance";
 Parameter XMLPREFIX = "xsi";
}

which produces the following, which  confuses me.

<soap:Envelope xmlns="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
</soap:Envelope>

Can anyone help, please?

Andy