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

<start>
  <element name="test" ns="http://example.com/1/">
    <zeroOrMore>
      <attribute>
        <choice>
          <nsName ns="http://example.com/1/"/>
          <nsName ns="http://example.com/2/"/>
        </choice>
        <text/>
      </attribute>
    </zeroOrMore>
  </element>
</start>

</grammar>