<element name="root" xmlns="http://relaxng.org/ns/structure/1.0">
  <oneOrMore>
    <element name="subelement">
      <choice>
        <element name="a">
	  <text/>
	</element>
	<zeroOrMore>
	  <element name="b">
	    <empty/>
	  </element>	  
	  <element name="c">
	    <empty/>
          </element>	  
	</zeroOrMore>
      </choice>
    </element>
  </oneOrMore>
</element>