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

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

<define name="cardContent">
  <element name="name">
    <text/>
  </element>
  <element name="emailAddress">
    <text/>
  </element>
</define>

</grammar>