Use libxml2 under linux to validate xpath against schema

Hello,

I have a question regarding programming libxml2 in C under linux.

Assume an XSD file called test.xsd:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="test" type="Test-Type"/>
    <xs:complexType name="Test-Type">
        <xs:all>
            <xs:element name="test-type-1"  type="xs:string"/>
            <xs:element name="test-type-2"  type="xs:integer"/>
        </xs:all>
    </xs:complexType>
</xs:schema>

And an XML file called test.xml:

<test>
  <test-type-1>foo</test-type-1>
  <test-type-2>1</test-type-2>
</test>


We can verify that this schema validates like this:
$ xmllint --noout --schema test.xsd test.xml
test.xml validates


It is trivial to write a program to validate an entire XML file against a schema.  For instance, if I can use this snippet:

  ctxt = xmlSchemaNewParserCtxt("test.xsd");
  schema=xmlSchemaParse(ctxt);

To verify the XSD file and then:
   
  doc = xmlReadMemory (xml_buf, strlen(xml_buf), NULL, NULL, 0);
  schemaErrors = xmlSchemaValidateDoc(ctxt, doc);
 
to validate the xml file against the XSD schema.  

So my question:  what if I want to validate not an ENTIRE xml document but only PART of one?  
I'd like to only check an xpath -- not an entire XML document -- for validation.  For instance, have a buffer containing:

"<test-type-2>10</test-type-2"

and validate that against the test.xsd file.  So if the buffer contained
"<test-type-2>foo</test-type-2>"

receive the libxml2 error message:

"Schemas validity error : Element 'test-type-2': 'foo' is not a valid value of the atomic type 'xs:integer'.
test.xml fails to validate"


I think the libxml2 function xmlSchemaValidateOneElement() is what I need to use, but I can't get it work.

Any thoughts or ideas?

Thanks!