Q:

How to render a4j outputpanel from iframe

I have a a4j:commandButton in a iframe and a a4j:outputPanel where both of the iframe and the panel resides in a same page.  Is it possible to reRender that panel on that button click? 
Thanks. 

A:

It looks to be not possible to be done using standard JSF+A4J approach.  The content inside of iframe is build by a separate request to separate view, so it has its own JSF components tree.  So a4j:commandButton and a4j:outputPanel are in different views (different components trees), and it is not possible to do 'cross-tree' rerender. 
To access parent page from iframe you can try using JavaScript. 
For example put to parent page jsFunction, like this:
<a4j:jsFunction name="reRenderPanel" reRender="panelId"/>

And in iframe add the following onclick javascript to commandButton:
<a4j:commandButton onclick="parent.reRenderPanel();"/>

