<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>