Generate Schematron "see" attribute value

I would like to dynamically generate the Schematron see attribute based on the the user home's directory. I could not get this working. Do you have an idea if this is possible? It needs to work in Oxygen XML. I am not sure if this is technically not possible in Schematron, or if this is a bug in Oxygen XML.

<?xml version="1.0" encoding="UTF-8"?>
<sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron" queryBinding="xslt2"
    xmlns:sqf="http://www.schematron-quickfix.com/validator/process">
    <sch:pattern>
        <sch:rule context="/">
            <sch:let name="x" value="if (contains(base-uri(), 'myname')) 
                then 'http://www.a.com' 
                else 'http://www.b.com'"/>
            <sch:report test="'a' = 'a'">
                Hello world: "<sch:value-of select="$x"/>"
            </sch:report>
        </sch:rule>
    </sch:pattern>
</sch:schema>

My goal is to generate a user-specific link to a locally deployed style guide, but, as you can see in the screenshot, the variable x is not resolved.

Maybe you can try to read the “user.home” system property: https://www.saxonica.com/html/documentation12/functions/fn/system-property.html