js ! tags

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html>
    <head>
        <title>first page</title>
        <script type="text/javascript">


        function getElements() {
            var x = document.getElementsByTagName("!");
            alert(x.length)
        }


        </script>
    </head>

    <body>
        <input type ="button" onclick="getElements()" value="push"/>

        <testTag id="test1">testing</testTag>
        <!>testing2</!>
        <!>testing3</!>
    </body>
</html>