how to append child to element using smooks groovy - groovy

Question

I am trying to use Smooks with Groovy to appendChild() to elements. So far I've been unable to do so.
Sample input file
<?xml version="1.0"?>
<orders>
<order res="0">
<header>
<date>Wed Nov 27 13:45:28 EST 2013</date>
<customer number="9404089839">Harish Nanda M</customer>
</header>
<orderitems>
<orderitem>
<product>007</product>
<quantity>7</quantity>
<price>7.90</price>
</orderitem>
<orderitem>
<product>005</product>
<quantity>3</quantity>
<price>7.20</price>
</orderitem>
</orderitems>
</order>
<order res="0">
<header>
<date>Wed Nov 27 13:45:28 EST 2013</date>
<customer number="2036139296">Sandesh G</customer>
</header>
<orderitems>
<orderitem>
<product>0023</product>
<quantity>87</quantity>
<price>57.90</price>
</orderitem>
<orderitem>
<product>005</product>
<quantity>3</quantity>
<price>7.20</price>
</orderitem>
</orderitems>
</order>
</orders>
Smooks config file
<?xml version="1.0"?>
<smooks-resource-list xmlns="http://www.milyn.org/xsd/smooks-1.1.xsd" xmlns:core="http://www.milyn.org/xsd/smooks/smooks-core-1.3.xsd" xmlns:g="http://www.milyn.org/xsd/smooks/groovy-1.1.xsd">
<core:filterSettings type="SAX"/>
<g:groovy executeOnElement="order">
<g:imports>
import org.milyn.xml.DomUtils;
import org.milyn.javabean.context.BeanContext;
import org.milyn.javabean.repository.BeanRepository;
import org.w3c.dom.*;
import groovy.xml.dom.DOMCategory;
import groovy.xml.dom.DOMUtil;
import groovy.xml.DOMBuilder;
import groovy.util.XmlSlurper;
</g:imports>
<g:script>
<!-- javax.xml.transform.dom.DOMSource source = new javax.xml.transform.dom.DOMSource(element);
javax.xml.transform.Transformer transformer = javax.xml.transform.TransformerFactory.newInstance().newTransformer();
javax.xml.transform.stream.StreamResult result = new
javax.xml.transform.stream.StreamResult(new java.io.StringWriter());
transformer.transform(source, result); String ss =
result.getWriter().toString(); def ord = new
XmlSlurper().parseText(ss) //ord.xxxx = "2222"; println
ord.orderitems.orderitem.product.text()*.toInteger().sum();
element.appendChild("res"); //element['#res'] = element.'#res'.toInteger() +
ord.orderitems.orderitem.product.text()*.toInteger().sum();
writeFragment(element);
-->
</g:script>
</g:groovy>
</smooks-resource-list>