<grammar xmlns="http://relaxng.org/ns/structure/1.0" ns="broken.rng">
  <start>
    <choice>
      <element name="foo">
        <element name="bar"><empty /></element>
      </element>

      <ref name="foo" />
    </choice>
  </start>

  <define name="foo">
    <element></element>
  </define>
</grammar>