gecko-dev/xpfe/browser/samples/collapsing.xul

<?xml version="1.0"?>
<?xml-stylesheet href="collapsing.css" type="text/css"?> 

<window xmlns:html="http://www.w3.org/1999/xhtml"
	xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
	xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
	orient="horizontal"
	onload="onWindowLoad()"> 

	<script>
	function onWindowLoad() {
		verifyControls();
	}
	function verifyControls() {
		var siteOne = window.frames["SiteOne"];
		var siteTwo = window.frames["SiteTwo"];
		if(siteOne==null)
			window.alert("Our SiteOne Frame isn't in the DOM!");
		if(siteTwo == null)
			window.alert("Our SiteTwo Frame isn't in the DOM!");
	}
	function cmdHideSiteOne(){
		verifyControls();
		window.document.getElementById("ShowSite").setAttribute("sitemode", "hideSiteOne");		
		verifyControls();
	}

	function cmdHideSiteTwo() {
		verifyControls();
		window.document.getElementById("ShowSite").setAttribute("sitemode", "hideSiteTwo");
		verifyControls();
	}
	</script>

	<broadcaster id="ShowSite" sitemode="hideSiteTwo" />
	<observes element="ShowSite" attribute="sitemode" />
	
	<vbox id="SiteOneBox" flex="1">
		<html:iframe flex="1" name="SiteOne" src="http://www.mozilla.org/xpfe/xptoolkit"/>
		<html:input type="BUTTON" value="Show Boxes Documentation" onclick="cmdHideSiteOne()"/>
	</vbox>
	<vbox id="SiteTwoBox" flex="1">
		<html:iframe flex="1" name="SiteTwo" src="http://www.mozilla.org/xpfe/xptoolkit/boxes.html"/>
		<html:input type="BUTTON" value="Show XPFE Documentation" onclick="cmdHideSiteTwo()"/>
	</vbox>
	
</window>