enveloping signature

Dear All,

If I have an arbitrary XML document, and I want to construct an enveloping 
signature over the entire document, what do you think would be appropriate 
handling of items outside the input document's root element?

For example, if I want to place the whole input document inside a 
dsig:Object element, would it make sense to include the XML declaration, 
the doctype declaration, comments and PIs?

Particularly regarding the DTD, should this perhaps be added to the top of 
the Signature document instead, with the Name changed to "dsig:Signature"?

Thanks,

Ari Kermaier