script.aculo.us---Effect.Opacity

This effect changes an element’s opacity (transparency).

作用 ：改变元素透明度

例子 ：new Effect.Opacity('id_of_element', {duration:0.5,from:1.0,to:0.7});

Will fade the element from 100% to 70% over the space of 1/2 second.

Microsoft Internet Explorer can only set opacity on elements that have a ‘layout’ -->>Giving Elements Layout

IE中只有layout的元素才能设置不透明值
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For Effect.Opacity based effects to work in Internet Explorer, you need to have give the affected elements the so-called ‘layout’ quality.The object that the filter is applied to must have layout before the filter effect displays. You can give the object layout by doing one of the following:

以下方法中可以使一个object layout 化
Setting the height or width property (doesn’t work on inline elements when the browser is not in quirksmode but in standards-compliant mode)
Setting the display property to inline-block
Setting the position property to absolute
Setting the writingMode property to tb-rl
Setting the contentEditable property to true

http://wiki.script.aculo.us/scriptaculous/show/Effect.Opacity