test/relaxng/tutor4_4.rng

<define name="inline">
  <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>
  <optional>
    <ref name="inline"/>
  </optional>
</define>