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

<define name="inline">
  <zeroOrMore>
    <choice>
      <text/>
      <element name="bold">
        <ref name="inline"/>
      </element>
      <element name="italic">
        <ref name="inline"/>
      </element>
      <ref name="inline.extra"/>
    </choice>
  </zeroOrMore>
</define>

<define name="inline.extra">
  <notAllowed/>
</define>

</grammar>