I want to understand whats different between this addressing pattern in jsf .
for example I have this xhtml structure :  
<h:panelGroup id="parent">
    <h:panelGroup id="child">
        <!-- 
          and some other components .
        -->
    </h:panelGroup>
</h:panelGroup>      
What is diff between this updates ?
   update="parent child"    
   update="parent:child"      
   update="parent,child"
 
    