Feathers HelloWorld example ported to MXML

HelloWorld.mxml

<?xml version="1.0" encoding="utf-8"?>
<f:Application xmlns:fx="http://ns.adobe.com/mxml/2009" 
	xmlns:f="library://ns.feathersui.com/mxml"
	theme="feathers.themes.MetalWorksMobileTheme">
	
	<f:layout>
		<f:VerticalLayout horizontalAlign="center" verticalAlign="middle"/>
	</f:layout>

	<f:Button id="button" label="Click Me"
		triggered="button_triggeredHandler(event)"/>
	
	<fx:Script>
	<![CDATA[
		import feathers.controls.Callout;
		import feathers.controls.Label;
		
		private function button_triggeredHandler(event:Event):void
		{
			var label:Label = new Label();
			label.text = "Hi, I'm Feathers!\nHave a nice day.";
			Callout.show(label, this.button);
		}
	]]>
	</fx:Script>
</f:Application>

Make sure the MXML namespace prefix matches on the layout property and the component where you're trying to pass in the layout. Notice how it's <f:Application> and <f:layout> with the f namespace prefix in my example code. If it were <ns:Application>, it would need to be <ns:layout>. The namespace prefix of a property must always match the namespace prefix of the component.

By the way, it appears that I don't get email notifications on Gists, so I didn't see your comment until now. Sorry for the late response.