I probably missing something trivial here.

I have an xml document with the doctype:

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet href="http://localhost/xslt/docbook/html/docbook.xsl"
type="text/xsl"?>
<!DOCTYPE book SYSTEM "../../System/DTD/main.dtd"[
  <!NOTATION XML SYSTEM "">
  <!NOTATION MIF SYSTEM "">
  <!NOTATION TIF SYSTEM "">
  <!NOTATION AI SYSTEM "">
  <!ENTITY % catalog PUBLIC "-//Siberlogic//ENTITIES V3.0.1//EN"
"file:///C:/xml/fips/catalog.pen">
  %catalog;
]>

On which I am going to run an identity transformation which is going to
do some filtering.

The question is - is can I keep the Doctype as is.

There are various xml:output options, but I seem to need to know what
the doctype is - and I really just want to pass it through.

If I have to define it - how do I define the part within the square
brackets. I( can see how to specify the rest but not that.

Thanks
Marcus