The pipeline
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" version="3.0">
<p:output port="result"/>
<p:identity>
<p:with-input select="*/text()[1]">
<doc>
<!-- A comment -->
<element1 att="att"/>
<?pi target?>
A text node
<element2/>
</doc>
</p:with-input>
</p:identity>
<p:cast-content-type content-type="application/xml">
<p:with-input select="p:document-properties(.)"/>
</p:cast-content-type>
</p:declare-step>
Schematron validation
<s:schema xmlns="http://www.w3.org/1999/xhtml" xmlns:s="http://purl.oclc.org/dsdl/schematron" queryBinding="xslt2">
<s:ns prefix="j" uri="http://www.w3.org/2005/xpath-functions"/>
<s:pattern>
<s:rule context="/">
<s:assert test="count(*) = 1">Document does not have exactly one child element.</s:assert>
<s:assert test="j:map">Root element is not named 'j:map'.</s:assert>
</s:rule>
<s:rule context="/j:map">
<s:assert test="j:string[@key='content-type']/text()='text/plain'">Content type is not text/plain.</s:assert>
</s:rule>
</s:pattern>
</s:schema>
