What is the XML rule for Block empty modify operations?

<rule>    <description>Block empty modify operations</description>    <conditions>        <and>            <if-operation op="equal">modify</if-operation>            <if-xpath op="not-true">modify-attr</if-xpath>          </and>      </conditions>    <actions>        <!-- Veto empty modify -->        <do-veto/>      </actions>  </rule>