What is the XML rule for userPrincipalName: reformat on Add/Modify?

<rule>    <description>userPrincipalName: reformat on Add/Modify</description>    <conditions>        <and>            <if-class-name mode="nocase" op="equal">User</if-class-name>            <if-operation mode="regex" op="equal">add|modify</if-operation>            <if-op-attr name="userPrincipalName" op="available"/>          </and>      </conditions>    <actions>        <do-reformat-op-attr name="userPrincipalName">            <arg-value type="string">                <token-join>                    <token-split delimiter=" ">                        <token-op-attr name="userPrincipalName"/>                      </token-split>                  </token-join>                <token-text xml:space="preserve">@</token-text>                <token-global-variable name="drv.domain.name"/>              </arg-value>          </do-reformat-op-attr>      </actions>  </rule>