<grammar xmlns="http://relaxng.org/ns/structure/1.0" ns="urn:test:simple.rng">
  <start>
    <element name="foo">
      <attribute name="name">
        <choice>
          <data type="string" />
          <choice>
            <value>id</value>
            <value>name</value>
            <value>content-type</value>
          </choice>
        </choice>
      </attribute>
    </element>
  </start>
</grammar>