mustella/Assets/Components/TrixSparkCheckBox.mxml

<?xml version="1.0" encoding="utf-8"?>
<s:CheckBox 
    xmlns:fx="http://ns.adobe.com/mxml/2009" 
    xmlns:mx="library://ns.adobe.com/flex/mx" 
    xmlns:s="library://ns.adobe.com/flex/spark" 
    label="Spark">
</s:CheckBox>