What is the XML rule for immutableId: Set if not present?

<rule>    <description>immutableId: Set if not present</description>    <conditions>        <and>            <if-class-name mode="nocase" op="equal">User</if-class-name>            <if-operation mode="nocase" op="equal">add</if-operation>            <if-op-attr name="immutableId" op="not-available"/>          </and>      </conditions>    <actions>        <do-set-local-variable name="query-back" scope="policy">            <arg-node-set>                <token-query class-name="User" datastore="src" scope="entry">                    <arg-dn>                        <token-src-dn/>                      </arg-dn>                    <arg-string>                        <token-text xml:space="preserve">GUID</token-text>                      </arg-string>                  </token-query>              </arg-node-set>          </do-set-local-variable>        <do-add-dest-attr-value name="immutableId">            <arg-value type="string">                <token-xpath expression="$query-back//attr[@attr-name=&quot;GUID&quot;]/value[1]/text()"/>              </arg-value>          </do-add-dest-attr-value>      </actions>  </rule>