To determine opacity, it is not enough to simply read a property value but some visual inpection is needed in order to verify if the property is applied. This is specially true in IE which is vey sensible to the syntax of the filter property.

idstylecommentexampleie6ie7ie8others
1filter:alpha(opacity=0) xxxx0001
2filter:alpha(opacity=20) xxxx0.20.20.21
3filter:alpha(opacity=100)xxxx1111
4filter:alpha(opacity=0) non positioned elementxxxx1111
5filter:alpha(opacity=20) non positioned elementxxxx1111
6filter:alpha(opacity=100)non positioned elementxxxx1111
7filter=progid:...:Alpha(Opacity=0) xxxx0001
8filter=progid:...:Alpha(Opacity=20) xxxx0.20.20.21
9filter=progid:...:Alpha(Opacity=100)xxxx1111
10filter:'progid:...:Alpha(Opacity=0)' xxxx1111
11filter:'progid:...:Alpha(Opacity=20)' xxxx1111
12filter:'progid:...:Alpha(Opacity=100)'xxxx1111
13-ms-filter=alpha(opacity=0) xxxx1111
14-ms-filter=alpha(opacity=20) xxxx1111
15-ms-filter=alpha(opacity=100)xxxx1111
16-ms-filter='alpha(opacity=0)' xxxx1101
17-ms-filter='alpha(opacity=20)' xxxx110.21
18-ms-filter='alpha(opacity=100)'xxxx1111
19-ms-filter=progid:...:Alpha(Opacity=0) xxxx1111
20-ms-filter=progid:...:Alpha(Opacity=20) xxxx1111
21-ms-filter=progid:...:Alpha(Opacity=100)xxxx1111
22-ms-filter='progid:...:Alpha(Opacity=0)' xxxx1101
23-ms-filter='progid:...:Alpha(Opacity=20)' xxxx110.21
24-ms-filter='progid:...:Alpha(Opacity=100)'xxxx1111
25opacity:0 xxxx1110
26opacity:0.5xxxx1110.5
27opacity:1 xxxx1111
28opacity:0 container opacity:0 xxxx1110
29opacity:0.5container opacity:0 xxxx1110
30opacity:1 container opacity:0 xxxx1110
31opacity:0 container opacity:0.5xxxx1110
32opacity:0.5container opacity:0.5xxxx1110.25
33opacity:1 container opacity:0.5xxxx1110.5
34opacity:0 container opacity:1 xxxx1110
35opacity:0.5container opacity:1 xxxx1110.5
36opacity:1 container opacity:1 xxxx1111