Flex中如何给RichTextEditor的元素添加TOOLTIP

<?xml version="1.0"?> 
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" 
        layout="vertical" 
        verticalAlign="middle" 
        backgroundColor="white"> 
  
    <mx:RichTextEditor id="richTextEditor" 
            title="I'm a rich text editor" 
            showToolTips="true" 
            fontFamilyToolTip="Select a font family." 
            fontSizeToolTip="Select a font size." 
            boldToolTip="I'm bold" 
            italicToolTip="I'm italic" 
            underlineToolTip="I'm an underline" 
            colorPickerToolTip="Select a color." 
            alignToolTip="Left | Center | Right | Justified" 
            bulletToolTip="I'm a bullet" 
            linkToolTip="I'm a link" /> 
  
</mx:Application>