First let me say I'm not asking the difference between div and span.
Basically I have an image, and on top of this image is a absolute positioned h3 element with a z-index of 2, in between the h3 and image I want to put a solid background color that is transparent, this is also absolute positioned with a z-index of 1. The reason I'm doing it this way vs. setting margin and padding properties of the h3 element is because I have the opacity property on the solid background set, if I do it that way the h3 element logically also turns semi-transparent, I don't want this to happen [also I'm using sIFR, and it calculates the size of the text based on the properties of the element it's replacing, this though is not really relevant]
The $10,000 question is should I use a div or span for the solid background, which would you consider more semantic? [even though what I'm doing is completely not semantic]