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

<start>
  <ref name="AddressBook"/>
</start>

<define name="AddressBook">
  <element name="addressBook">
    <zeroOrMore>
      <ref name="Card"/>
    </zeroOrMore>
  </element>
</define>

<define name="Card">
  <element name="card">
    <ref name="Name"/>
    <ref name="Email"/>
  </element>
</define>

<define name="Name">
  <element name="name">
    <text/>
  </element>
</define>

<define name="Email">
  <element name="email">
    <text/>
  </element>
</define>

</grammar>