<element name="card" xmlns="http://relaxng.org/ns/structure/1.0">
  <element name="name">
    <text/>
  </element>
  <element name="email">
    <text/>
  </element>
  <element name="preferredFormat">
    <choice>
      <value>html</value>
      <value>text</value>
    </choice>
  </element>
</element>