<element name="example" xmlns="http://relaxng.org/ns/structure/1.0">
  <zeroOrMore>
    <attribute>
      <anyName>
        <except>
          <name>xml:space</name>
        </except>
      </anyName>
    </attribute>
  </zeroOrMore>
  <optional>
    <attribute name="xml:space">
      <choice>
        <value>default</value>
        <value>preserve</value>
      </choice>
    </attribute>
  </optional>
</element>