p:store and <!DOCTYPE ...>

I'm trying to p:store some XML with a doctype declaration. To demonstrate,
this is the essence of what I've got:


<?xml version="1.0" encoding="UTF-8"?>
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc"
    xmlns:c="http://www.w3.org/ns/xproc-step" version="1.0">
    <p:input port="source">
        <p:inline>
            <xhtml/>
        </p:inline>
    </p:input>
    <p:output port="result"/>

    <p:store name="storestep">
        <p:with-option name="href"
select="resolve-uri('/home/jostein/Skrivebord/testoutput.xml')"/>
        <p:with-option name="doctype-public" select="'-//W3C//DTD XHTML 1.0
Transitional//EN'"/>
    </p:store>

    <p:identity>
        <p:input port="source">
            <p:pipe port="result" step="storestep"/>
        </p:input>
    </p:identity>
</p:declare-step>


This gives:


<xhtml xmlns:c="http://www.w3.org/ns/xproc-step"/>


...but no doctype declaration... How can I get a doctype declaration in my
output?

Regards
Jostein Austvik Jacobsen