[xml] xml:lang attribute with xmllint

["Verachten Bruno" <Bruno Verachten atosorigin com>]

Hi,

I've just generated a schema with elements like this one :
<xs:element name="origin">
 <xs:complexType>
  <xs:simpleContent>
   <xs:extension base="xs:string">
    <xs:attribute ref="xml:lang" use="required"/>
   </xs:extension>
  </xs:simpleContent>
 </xs:complexType>
</xs:element>

As you can see, there is an attribute-ref to the xml:lang attribute.
This attribute is not defined in the schema, and the IBM SchemaQualityChecker
doesn't see any error in the schema.

I'm trying to validate an XML document with this schema, and I get an error with xmllint :
$ xmllint --schema ../doc/translation.xsd --noout example12.xml
../doc/translation.xsd:22: element attribute: Schemas parser error : Schemas: attribute anonattr 9 reference 
lang not found
../doc/translation.xsd:40: element attribute: Schemas parser error : Schemas: attribute anonattr 17 reference 
lang not found
../doc/translation.xsd:30: element attribute: Schemas parser error : Schemas: attribute anonattr 13 reference 
lang not found
WXS schema ../doc/translation.xsd failed to compile

Is there a problem with xmllint and the xml:lang attribute, or did I miss something?
$ xmllint --version
xmllint: using libxml version 20609
   compiled with: DTDValid FTP HTTP HTML C14N Catalog XPath XPointer XInclude Iconv Unicode Regexps Automata 
Schemas

Thanks.

Bruno Verachten