The pipeline
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" version="3.0">
<p:output port="result"/>
<p:insert match="a" position="first-child">
<p:with-input>
<p:inline>
<root>
<a>
<d/>
</a>
</root>
</p:inline>
</p:with-input>
<p:with-input port="insertion">
<p:inline>
<b/>
</p:inline>
<p:inline>
<c/>
</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/a">Root element does not have child element 'a'.</s:assert>
<s:assert test="root/a/*[1]/name()='b'">Name of the first element of a is not 'b'.</s:assert>
<s:assert test="root/a/*[2]/name()='c'">Name of the second element of a is not 'c'.</s:assert>
<s:assert test="root/a/*[3]/name()='d'">Name of the third element of a is not 'd'.</s:assert>
</s:rule>
</s:pattern>
</s:schema>
