<grammar xmlns=“relaxng.org/ns/structure/1.0”>

<start>
  <ref name="root"/>
</start>
<define name="root">
  <element name="root">
    <interleave>
      <element name="e1">
        <text/>
      </element>
      <externalRef href="rngbug-001.ext"/>
    </interleave>
  </element>
</define>

</grammar>