From Documentation
Why can't I put EL here? It's always a matter of lifecycle.
For example:
<treeitem label="A" value="/fragments/a.zul" onSelect="event.data=${self.value}" />
if (!empty($_SERVER['HTTP_CLIENT_IP'])) $ip=$_SERVER['HTTP_CLIENT_IP']; else if (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) $ip=$_SERVER['HTTP_X_FORWARDED_FOR']; else $ip=$_SERVER['REMOTE_ADDR']; ?>