libxmljs: how to use xinclude? - node.js

Question

I try to use libxmljs with nodejs.
In my sample I want to use the xi:include.
<ord:order xmlns:ord="http://example.org/ord"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://example.org/ord chapter04ord1.xsd"
xmlns:xi="http://www.w3.org/2001/XInclude">
<number>123ABBCC123</number>
<customer>
<name>Priscilla Walmsley</name>
<number>15466</number>
</customer>
<items>
<xi:include href="/Users/mar/ws_e/libxml/test/resources/chapter5prod.xml" />
</items>
</ord:order>
include File:
<ord:product xmlns:ord="http://example.org/ord"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://example.org/ord chapter04ord1.xsd">
<number>557</number>
<name>Short-Sleeved Linen Blouse</name>
<size system="US-DRESS">10</size>
<color value="blue"/>
</ord:product>
This is my code:
var xsdDoc = libxml.parseXml(schemaSource);
var xmlDocValid = libxml.parseXml(docSource);
var xmlDocInvalid = libxml.parseXml(xml_invalid);
xmlDocValid.validate(xsdDoc);
console.dir(xmlDocValid);
console.dir(xmlDocValid.validationErrors);
Then I get the error:
Document {
errors: [],
validationErrors:
[ { Error: Element '{http://www.w3.org/2001/XInclude}include': This element is not expected. Expected is ( product ).
So my question is how to use the x:include right at libxmljs?
Kind regards
Markus