[XML-SIG] DOCTYPEs question with 4DOM

[Derek Fountain]

According to my book (Inside XML, New Riders) a document type declaration can 
have one of several forms:

<!DOCTYPE rootname [DTD]>
<!DOCTYPE rootname SYSTEM url>
<!DOCTYPE rootname SYSTEM url [DTD]>
<!DOCTYPE rootname PUBLIC identifier>
<!DOCTYPE rootname PUBLIC identifier [DTD]>

According to the DOM Level 3 specification, the createDocumentType method of 
the DOMImplementation interface takes 3 parameters: qualified name, publicId 
and systemId. I would have thought that rootname is the qualified name, 
publicId is the identifier (in the last two cases) and systemId is the url 
(in the 2nd and 3rd cases). I could be wrong, but that made sense. :o}

I want to create a doctype like this:

<!DOCTYPE test>

so I'd have thought that, using the 4DOM implementation from Python, I could 
say:

docType = implementation.createDocumentType( "test", None, None )

but when serialised, that doesn't produce a DOCTYPE line at all. This produces 
what I want:

docType =  implementation.createDocumentType( "", "test", "" )

and this:

docType =  implementation.createDocumentType( "1", "test", "2" )

produces:

<!DOCTYPE storage PUBLIC "test" "2">

with the "1" nowhere to be seen.

I have no idea what is going on. Can someone explain? Thanks! :o)