Does not support xs:key (keyRef NoIllegalEntries)

XMLBeans does not support the <xs:key name=""> feature used in XSD Schema. I have tried multiple schemas using this feature and when I go to validate an XML document, I get the same error:

Key '<the-name-of-your-key' not found (keyRef NoIllegalEntries)

I am sure this is valid syntax as XML Spy and other editors are ok with the key ref tag as this is supported within XSD.

I have included a sample XSD and XML document that includes these values.

<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<xsd:element name="supermarket">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="aisle" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="item" maxOccurs="unbounded">
<xsd:complexType>
<xsd:simpleContent>
<xsd:extension base="xsd:string">
<xsd:attribute name="code" type="xsd:positiveInteger"/>
<xsd:attribute name="quantity" type="xsd:positiveInteger"/>
<xsd:attribute name="price" type="xsd:decimal"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
</xsd:element>
</xsd:sequence>

<!-- Attribute Of Aisle -->
<xsd:attribute name="name" type="xsd:string"/>
<xsd:attribute name="number" type="xsd:positiveInteger"/>
<!-- Of Aisle -->

</xsd:complexType>

<xsd:keyref name="NoIllegalEntries" refer="itemKey">
<xsd:selector xpath="item"/>
<xsd:field xpath="@code"/>
</xsd:keyref>
</xsd:element>
<xsd:element name="items">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="item" maxOccurs="unbounded">
<xsd:complexType>
<xsd:simpleContent>
<xsd:extension base="xsd:string">
<xsd:attribute name="code" type="xsd:positiveInteger"/>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
<xsd:attribute name="name" type="xsd:string"/>
</xsd:complexType>
<xsd:key name="itemKey">
<xsd:selector xpath="items/item"/>
<xsd:field xpath="@code"/>
</xsd:key>
</xsd:element>
</xsd:schema>

***********************
and sample XML
***********************
<?xml version="1.0" encoding="UTF-8"?>
<!--Sample XML file generated by XMLSPY v5 rel. 4 U (http://www.xmlspy.com)-->
<supermarket xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="C:\tmp\Supermarket.xsd" name="String">
<aisle name="String" number="2">
<item code="1234" quantity="2" price="3.1415926535897932384626433832795">String</item>
</aisle>

<items>
<item code="1234">Java</item>
</items>
</supermarket>