I am newbie.
many of javascript code start with <!--
<script type="text/javascript">
<!--
and finish with //-->
//-->
</script>
I think the reason is for compatibility.
But I cannot find the clue in any books.
even I cannot find anything with google.
No. This is a holdover from the days when Netscape 2 was common.
It isn’t needed with any browser that can function on the web today, and it is positively harmful in XHTML.
I wrote a longer explanation last year.