Please describe the problem:
I have a simple xml schema that uses key/keyref to constrain identity.

In the schema I have defined an attribute called name on the root element.

When the optional name attribute is present in the root element an invalid xml
file (invalid keyref value) passes validation. If the root element name
attribute is removed from the xml the validation fails as expected.

The behaviour is consistent between xmllint and my own application which calls
the libxml2 API directly.

As an aside, xmlspy validates the file correctly whether the root element
attribute is present or not.

Steps to reproduce:
1. xmllint  -noout -schema test.xsd test.xml
2. "test.xml validates"
3. Remove the root element attribute Name="test"
4. xmllint  -noout -schema test.xsd test.xml
5. test.xml:2: element family: Schemas validity error : Element 'family': No
match found for key-sequence ['annie'] of key reference 'sibling_key_ref'.
test.xml fails to validate: 1877


Actual results:
As above.

Expected results:
I expect the validation error reported in step 5 to be reported whether or not
the root element attribute is present.

Does this happen every time?
Yes

Other information:
<?xml version="1.0" encoding="ISO-8859-1"?>
<family xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="test.xsd" name="test">
    <siblings>
    	<sibling name="gill"/>
    </siblings>
    <sisters>
    	<sister name="gill"/>
    	<sister name="annie"/>
    </sisters>
</family> 


<?xml version="1.0" encoding="ISO-8859-1"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <xs:element name="family" type="family_type">
      <xs:key name="sibling_key">
        <xs:selector xpath="siblings/sibling"/>
        <xs:field xpath="@name"/>
      </xs:key>
      <xs:keyref name="sibling_key_ref" refer="sibling_key">
        <xs:selector xpath="sisters/sister"/>
        <xs:field xpath="@name"/>
    </xs:keyref>
  </xs:element>
    <xs:complexType name="family_type">
      <xs:sequence>
        <xs:element name="siblings" type="siblings_type" />
        <xs:element name="sisters" type="sisters_type"  />
      </xs:sequence>
      <xs:attribute name="name" type="xs:string"/>
    </xs:complexType>
    <xs:complexType name="siblings_type">
      <xs:sequence>
        <xs:element name="sibling" type="sibling_type" minOccurs="0"  
maxOccurs="unbounded" />
      </xs:sequence>
    </xs:complexType>    
    <xs:complexType name="sisters_type">
      <xs:sequence>
        <xs:element name="sister" type="sister_type" minOccurs="0"  
maxOccurs="unbounded" />
      </xs:sequence>
    </xs:complexType>        
	<xs:complexType name="sibling_type">
		<xs:attribute name="name" type="xs:string"/>
	</xs:complexType>
	<xs:complexType name="sister_type">
		<xs:attribute name="name" type="xs:string"/>
	</xs:complexType>    
</xs:schema>