Markup: a<sup>4</sup>a<span class=sup>4</span>
a<sup>4</sup>a<span class=sup>4</span>
Style: sup, .sup { vertical-align: super; font-size: 80% }
sup, .sup { vertical-align: super; font-size: 80% }
Rendering: a4a4
View the source code to see the script that fixes the sizing of sup on IE, by turning it to span with style.
sup
span