Useful simple type for Global Unique Identifier

Keep having to use this in schemas - so thought I would put this here..

This type will verify a global unqiue identifier:

<xs:simpleType name="GUID">
    <xs:annotation>
        <xs:documentation xml:lang="en">The representation of a GUID, generally the id of an element.</xs:documentation>
    </xs:annotation>
    <xs:restriction base="xsd:string">
        <xs:pattern
            value="\{[a-fA-F0-9]{8}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{12}\}"/>
    </xs:restriction>
</xs:simpleType>