<grammar xmlns="http://relaxng.org/ns/structure/1.0">

<define name="cell.content">
  <notAllowed/>
</define>

<start>
  <element name="table">
    <oneOrMore>
      <element name="tr">
        <oneOrMore>
	  <element name="td">
	    <ref name="cell.content"/>
	  </element>
        </oneOrMore>
      </element>
    </oneOrMore>
  </element>
</start>

</grammar>