<grammar root="order_pizza" xml:lang="en-US">
  <rule id="topping">
    <one-of>
      <item>onions</item>
      <item>cheese</item>
    </one-of>
  </rule>

  <rule id="order_pizza" scope="public">
    <item>
      <ruleref uri="#topping"/>
      <item>P1zz@</item>
      <item>please</item>
    </item>
  </rule>
</grammar>