'all' within 'complexContent' -- which parser is correct?

Hi!

Here is a schema:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:complexType name="BaseParent">
    <xs:sequence>
      <xs:element name="child1"/>
    </xs:sequence>
  </xs:complexType>
  <xs:element name="parent">
    <xs:complexType>
      <xs:complexContent>
        <xs:extension base = "BaseParent">

          <!-- XERCES's SAXParser reports error here-->
          <xs:all>
            <xs:element name="child2"/>
          </xs:all>
          
        </xs:extension>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
</xs:schema>

XMLSpy5 and MSXML4 loaded it successfully but
XERCES-C++ failed with error: "An 'all' model group that's part of
a complex type definition must constitute the entire content type of
the definition" :-(

Who's right?

thanks in advance.