test/relaxng/tutor4_3.rng

<define name="inline" xmlns="http://relaxng.org/ns/structure/1.0">
  <zeroOrMore>
    <choice>
      <text/>
      <element name="bold">
        <ref name="inline"/>
      </element>
      <element name="italic">
        <ref name="inline"/>
      </element>
      <element name="span">
        <optional>
          <attribute name="style"/>
        </optional>
        <ref name="inline"/>
      </element>
    </choice>
  </zeroOrMore>
</define>