Il Document Object Model di Internet Explorer

Importo iva esclusa: 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
	<head>
		<title>
			Internet Explorer DOM
		</title>
	</head>
	<body>
		<h1>
			Il Document Object Model di Internet Explorer
		</h1>
		<form name="calcolo">
			Importo iva esclusa:
			<input type="text" name="importo" style="text-align: right" value="1000">
			<input type="button" name="calcolo" value="Calcola iva" onClick="javascript:alert('L\'importo dell\'iva è ' + document.calcolo.importo.value*0.2);">
		</form>

	</body>
</html>