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<!DOCTYPE html>
<html>
<head>
<script type="text/javascript">
function doRollover() {
var o = document.getElementsByTagName("div")[1];
var x = document.getElementById("MyDiv1");
o.className = ( o.className == 'Class1' ) ? 'Class2' : 'Class1';
x.innerHTML = o.getAttribute("class")
}
</script>
</head>
<body>
<div id="MyDiv1"></div></br>
<div class="Class1">Hello world!</div><p>
<button type="button" onclick="doRollover()">rollover class name</button>
</body>
</html>
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