document.getElementById('display').style.clip="rect(" + (startPosition + 1) + " 100 " + (startPosition + endPosition) + " 0)"
<html>
<head>
<style>
span
{
font:12px arial;
background:#CCCCCC;
position:absolute;
width:100;
height:500;
top:100;
clip:rect(0 100 100 0);
}
</style>
<script type="text/javascript">
var interval
startPosition=0
topPosition=100
endPosition=100
speed=50
function scrollit()
if (startPosition!=200)