i want the p background to be transparent but not affect the span text. so far with the combinations i've tried, changing the opacity on the p element changes the span text.

why doesn't span styles keep the span text 100% trasparency free, in other words, with 0 opacity applied, fully visible?

Code HTML4Strict:
<p><span>text</span></p>

Code CSS:
p{
    background: #000;
    color: #fff;
    width: 100%;
    /* transparent - need hasLayout for ie ( zoom: 1; ) I have width set above */
    filter: alpha(opacity=70);
    opacity: 0.7;
}
p span{
    filter: alpha(opacity=100);
    opacity: 1.0;
}