1. data document which we want to sort
2. the stylesheet document

<xf:model>
  <xf:instance id="default-instance">
    <data xmlns="">
      <item>
        <name>B-item</name>
        <date>2001-05-03</date>
      </item>
      <item>
        <name>A-item</name>
        <date>2005-05-03</date>
      </item>
      <item>
        <name>Z-item</name>
        <date>2003-05-03</date>
      </item>
      <item>
        <name>D-item</name>
        <date>2002-05-03</date>
      </item>
    </data>
  </xf:instance>
          
  <xf:instance id="stylesheet">
    <xsl:stylesheet
      xmlns="" 
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
      version="1.0">
      <xsl:template match="/">
        <data>
          <xsl:apply-templates select="data/item">
            <xsl:sort type="string" select="name"/>
          </xsl:apply-templates>
        </data>
      </xsl:template>
                  
      <xsl:template match="*|@*|text()">
        <xsl:copy>
          <xsl:apply-templates select="*|text()|@*"/>
        </xsl:copy>
      </xsl:template>
    </xsl:stylesheet>
  </xf:instance>
</xf:model>

function sort_instance(id) {
  // We get the instance element
  var instanceElement = document.getElementById(id);
  if (instanceElement!=null) {
    // XForms exposes the retrival of the instance document from the model element which *should*
   // be the parent for the instance element.
   var instance = instanceElement.parentNode.getInstanceDocument(id);
   if (instance!=null) {
      // Now creating the stylesheet, for this example the stylesheet document is also an instance
      // by it can be loaded from many difference sources
      var xslDom = instanceElement.parentNode.getInstanceDocument('stylesheet');
			
      // create an XSLTProcessor and attach the stylesheet
      var processor = new XSLTProcessor()
      processor.importStylesheet(xslDom);
	
      // now we do the sorting transformation
      var resultDom = processor.transformToDocument(instance, instance);
			
      // we then move the result info the instance dom
      instance.removeChild(instance.documentElement);
      instance.appendChild(resultDom.documentElement);
			
      // and performs the updates for XForms
      instanceElement.parentNode.rebuild();
      instanceElement.parentNode.recalculate();
      instanceElement.parentNode.revalidate();
      instanceElement.parentNode.refresh();
    }
  }
}

1. I needed a gallery for my site
2. I wanted to make a real AJAX application to compare it with XForms/a declarative approach.