<?xml version=“1.0”?> <Foo

    xmlns="urn:test:foo"
    xmlns:foo="urn:test:foo"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:test:foo idc-keyref_1.xsd">

<Def>
    <Link foo:linkKey="L4"/>
</Def>

<Ref foo:linkRef="L4"/>

</Foo>