<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>