<xsd:attribute name="featureVersion" type="xsd:string" use="optional">
    <xsd:annotation>
        <xsd:documentation>

              For systems that implement versioning, the featureVersion

              attribute is used to specify which version of a particular

              feature instance is to be retrieved.  A value of ALL means

              that all versions should be retrieved.  An integer value

              'i', means that the ith version should be retrieve if it

              exists or the most recent version otherwise.

           </xsd:documentation>
    </xsd:annotation>
</xsd:attribute>