When I extend an MX class in Flex, how do I reference it in the MXML?

<mx:Tree>
    <!-- ... -->
</mx:Tree>

class ChristmasTree extends mx.controls.Tree {
    // ...
}

package myComponents
{
    // as/myComponents/TextAreaFontControl.as
    import mx.controls.TextArea;

    public class TextAreaFontControl extends TextArea
    {

        // add / change behaviour, properties etc. ...

    }

}

<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
   xmlns:MyComp="myComponents.*">

<!-- ... -->

<MyComp:TextAreaFontControl />

<?xml version="1.0" encoding="utf-8"?>
<mx:TextArea xmlns:mx="http://www.adobe.com/2006/mxml">
    <!-- her comes the Script block and other suff -->
</mx:TextArea>