Flex Button CSS skinning

I have a CSS file containing the following definition :

.Tab{
    up-skin:Embed(skinClass='XUpSkin');
    over-skin:Embed(skinClass='XOverSkin');
    disabled-skin:Embed(skinClass='XDisabledSkin');
}

And a Flex file : 开发者_JS百科

<mx:Button id="b1" style="Tab"/>

Now, I want to use the disabled-skin defined in the CSS, as the upSkin of b1.

So something like

b1.setStyle("upSkin","Tab.disabled-skin");

But I am struggling with the exact syntax of the second argument for setStyle.

What should I use for the second argument for setStyle method?

b1.setStyle("upSkin", b1.getStyle("disabled-skin") );