Kolyaj,
Наверно не text а data или nodeValue
Вариант для IE ...
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
</head>
<body>
<script type="text/javascript">
var Doctype =/CSS/.test(document.compatMode)&&document.getElementsByTagName('!')[0].data;
document.write(Doctype)
</script>
</body>
</html>