test.mxml

<?xml version="1.0" encoding="utf-8"?>
<!-- HelloWorld.mxml -->
<s:Application 
    xmlns:fx="http://ns.adobe.com/mxml/2009" 
    xmlns:s="library://ns.adobe.com/flex/spark" 
    xmlns:mx="library://ns.adobe.com/flex/mx" 
    width="200" height="160">
    <s:Panel title="My Application" width="100%">
        <s:layout>
            <s:VerticalLayout paddingTop="10" horizontalAlign="center"/>
        </s:layout>
        <s:Label text="Hello World!" fontWeight="bold" fontSize="24"/>
    </s:Panel>
</s:Application>
<!-- Compiled with: "mxmlc --strict=true --file-specs test.mxml" -->