The pipeline
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" version="3.0">
<p:output port="result"/>
<p:insert match="processing-instruction('that')" position="before">
<p:with-input>
<p:inline>
<root>
<?that is a pi?>
</root>
</p:inline>
</p:with-input>
<p:with-input port="insertion">
<p:inline>
<root1/>
</p:inline>
<p:inline>
<root2/>
</p:inline>
</p:with-input>
</p:insert>
</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:pattern>
<s:rule context="/">
<s:assert test="root">The root element is not 'root'.</s:assert>
<s:assert test="root/*[1]/name()='root1'">Name of the first element of root is not 'root1'.</s:assert>
<s:assert test="root/*[2]/name()='root2'">Name of the second element of root is not 'root2'.</s:assert>
<s:assert test="root/root2/following-sibling::processing-instruction('that')">There is no PI behind the second inserted document.</s:assert>
</s:rule>
</s:pattern>
</s:schema>
