You can set stuff on the action tag by using nested webwork:param's...

<webwork:action name="'UserDetail'">
<param name="user">username</param>
</webwork:action>

useful if you want to the access stuff from the action using one of The Three Uses Of The Property Tag...

<ww:action name="'UserDetail'">
    <ww:param name="user">username</ww:param>
    <ww:property name="firstName"/>
    <ww:property name="lastName />
</ww:action>