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

<start>
  <element name="addressBook">
    <zeroOrMore>
      <element name="card">
        <ref name="card.attlist"/>
      </element>
    </zeroOrMore>
  </element>
</start>

<define name="card.attlist" combine="interleave">
  <attribute name="name">
    <text/>
  </attribute>
</define>

<define name="card.attlist" combine="interleave">
  <attribute name="email">
    <text/>
  </attribute>
</define>

</grammar>