<SOAP:Envelope xmlns:SOAP="http://www.w3.org/2003/05/soap-envelope">
    <SOAP:Header>
        <CachePolicy xmlns="http://www.example.org/cache-policy" SOAP:role="http://www.example.org/gateway/cache" SOAP:mustUnderstand="true">
            <RequestETag>686897696a7c876b7e</RequestETag>
            <MaxAge>3600</MaxAge>
        </CachePolicy>
    </SOAP:Header>
    <SOAP:Body>
        <Lookup xmlns="http://www.acme.co.uk/postcode-lookup">
            <Postcode>SW1A 1AA</Postcode>
        </Lookup>
    </SOAP:Body>
</SOAP:Envelope>
