Con Explorer non mi considera il valore size="1" per HR, come posso fare?

codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
</head>
<body>
<hr width="100%" size="1" noshade="noshade" />
</body>
</html>