How to generate doctype declarations dynamically i

Requirement:

Is to add correct Doctype declaration on the output xml [The root element of the input xml can be chapter or section element]. For Instance, consider the chapter element public identifier is PUBLIC "-//OASIS//DTD DocBook Chap XML V4.5//EN" and system identifier is "chap.dtd". Simillary for section element public identifier is PUBLIC "-//OASIS//DTD DocBook Sec XML V4.5//EN" and system identifier is "sec.dtd".

Input XML1: chapter.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook Chap XML V4.5//EN" "chap.dtd">
<chapter>
    <title>Chapter Template Title</title>
    <para>Text</para>
    <section>
        <title>Section Title</title>
        <para>Section text</para>
    </section>
</chapter>

Input XML2: section.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook Chap XML V4.5//EN" "chap.dtd">
<section>
    <title>Section Title</title>
    <para>Section text</para>
</section>

XSLT file: test.xsl:

Stylesheet just copies input xml to output and adds @sec on all section elements Stylesheet adds correct doctype declaration to output xml, because the input xml root element can be or element

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">

<xsl:template name="add-doctype-declaration">
    <xsl:choose>
        <xsl:when test="/chapter">
            <xsl:text disable-output-escaping="yes">
&lt;!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook Chap XML V4.5//EN" "chap.dtd"&gt;
</xsl:text>
        </xsl:when>
        <xsl:when test="/section">
            <xsl:text disable-output-escaping="yes">
&lt;!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook Sec XML V4.5//EN" "sec.dtd"&gt;
</xsl:text>
        </xsl:when>
    </xsl:choose>
</xsl:template>

<xsl:template match="/">
    <xsl:call-template name="add-doctype-declaration"/>
    <xsl:apply-templates/>
</xsl:template>

<!-- Identity Template -->
<xsl:template match="@*|*|processing-instruction()">
    <xsl:copy>
        <xsl:apply-templates select="@*|node()"/>
    </xsl:copy>
</xsl:template>

<xsl:template match="section">
    <xsl:copy>
        <xsl:apply-templates select="@*"/>
        <xsl:attribute name="sec">
            <xsl:number/>
        </xsl:attribute>
        <xsl:apply-templates/>
    </xsl:copy>
</xsl:template>

</xsl:stylesheet>

Expected output.xml for Input XML1

<?xml version="1.0" encoding="utf-8"?> Input XML1:
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook Chap XML V4.5//EN" "chap.dtd">
<chapter>
    <title>Chapter Template Title</title>
    <para>Text</para>
    <section sec="1">
        <title>Section Title</title>
        <para>Section text</para>
    </section>
</chapter>

Expected output.xml for Input XML2

<?xml version="1.0" encoding="utf-8"?> Input XML1:
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook Sec XML V4.5//EN" "sec.dtd">
<section sec="1">
    <title>Section Title</title>
    <para>Section text</para>
</section>

Using any XSLT engine, the transformation works absolutely fine, and able to get the expected output

But, if the transformation is done through XProc I end up with the following error. Can someone help in resolving this error

err:XD0001 : XD0001 It is a dynamic error if a non-XML resource is produced on a step output or arrives on a step input.

XProc file: test.xpl

<?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" name="testing">
    <p:input port="source">
       <p:document href="chapter.xml"/>
    </p:input>
    <p:output port="result">
        <p:empty/>
    </p:output>

    <p:xslt version="1.0" name="transform">
        <p:input port="stylesheet">
            <p:document href="test.xsl"/>
        </p:input>
        <p:input port="parameters">
            <p:empty/>
        </p:input>
    </p:xslt>

   <!-- Assume that there is another transform happening for chapter/section xml -->
   <p:xslt version="1.0" name="transform2">
        <p:input port="stylesheet">
            <p:document href="test2.xsl"/>
        </p:input>
        <p:input port="parameters">
            <p:empty/>
        </p:input>
    </p:xslt>


    <p:store omit-xml-declaration="false" encoding="utf-8" name="serialize">
        <p:with-option name="href" select="output.xml"/>
    </p:store>

</p:declare-step>

Again look at

Here is two simple examples that shows that you don't need to contextualize the Doctype generation

Section http://www.sharexml.com/x/get?k=uWn0KA7RThnt

Chapter http://www.sharexml.com/x/get?k=wAJlbUJfzIYQ

[UPDATED AFTER ANSWER]

And if you want that doctype change dynamically

Section http://www.sharexml.com/x/get?k=pBAwCds86RnQ

Chapter http://www.sharexml.com/x/get?k=JHEWghzgWIq1

Hope this helps