title: Adding a mask to a Flex Image
body: <p>I have the following mxml:</p>
  
  <pre><code>&lt;s:Image source="@Embed(source='my/path/to/img.png')" &gt;
    &lt;flex:mask&gt;
      &lt;s:Group alpha="0.1"&gt;
        &lt;s:Rect width="129" height="123"&gt;
          &lt;s:fill&gt;
            &lt;s:SolidColor color="0x00FFFF"/&gt;
          &lt;/s:fill&gt;
        &lt;/s:Rect&gt;
      &lt;/s:Group&gt;
    &lt;/flex:mask&gt;
  &lt;/s:Image&gt;
  </code></pre>
  
  <p>Shouldn't this code generate a Rectangular Mask of 129px*123px that will produce a cropping effect?</p>
  
  <p>Thanks.</p>