XML Schema (xsd)

Damn those documents get hefty quick, and I can’t quite seem to find a way to say a given element has an attribute that should reference an element in another container.

<!-- Given: -->

<xs:element name="Languages">
<xs:complexType>
<xs:sequence>
<xs:element name="Language">
<xs:complexType>
<xs:attribute name="Code" type="xs:language" use="required"/>
<!-- ... -->
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
<xs:element>

<!-- How do you bind ... ->
<xs:element name="Translations">
...
<xs:element name="Translation">
...
<xs:attribute name="Language" ref="/Languages/Language" refkey="Code"/>

Or is this validation just something you have to do yourself in code?