I still can not validate xml that uses xml schema extensions. I think I figured out what the problem might be, but do not know how to resolve i. I wonder if the problem is with the way I set up my xml namespace?

<zoo:cageRequest xmlns:zoo="http://www.example.org/Zoo" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

I am setting up the xml schema namespace the same way eclipse does when you create a new XSD or XML file. I entered http://www.w3.org/2001/XMLSchema-instance in the address bar of my browsers and got quite a surprise!

 <xs:annotation>
  <xs:documentation><p>This schema should never be used as such:
                    <a href="http://www.w3.org/TR/xmlschema-1/#no-xsi">the XML
                    Schema Recommendation</a> forbids the declaration of
                    attributes in this namespace</p>

  </xs:documentation>
 </xs:annotation>

http://www.w3.org/TR/xmlschema-1/#no-xsi is very confusing.

where does libxml get the schema lang schema/dtd? As a test I put some typos in my xsd file. libxml generated an error when I tried to validate the xsd file as expected?

what URL should I be using?

Do I need to make a special call to cause the libxml to use this other location?

My app will be running on a private network and not have access to www.w3.org, Do I need to copy a dtd or something to my local env?