The pipeline
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" version="3.0">
<p:output port="result"/>
<p:set-properties properties="map{'base-uri' : 'http://www.new-base-uri.test'}">
<p:with-input>
<p:inline content-type="text/plain" xml:base="http://www.old-base-uri.test">Some text.</p:inline>
</p:with-input>
</p:set-properties>
<p:identity>
<p:with-input>
<result>
<base-uri>{base-uri(.)}</base-uri>
<property>{p:document-property(., 'base-uri')}</property>
</result>
</p:with-input>
</p:identity>
</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="result">The document root is not result.</s:assert>
<s:assert test="result/base-uri/text()= 'http://www.new-base-uri.test'">Document's base-uri is wrong.</s:assert>
<s:assert test="result/property/text()= 'http://www.new-base-uri.test'">Document property base-uri is wrong.</s:assert>
</s:rule>
</s:pattern>
</s:schema>
