[TTayfun]

hello guys,
i see in headinclude template

<script type="text/javascript">
<!--
var SESSIONURL = "$session[sessionurl_js]";
var SECURITYTOKEN = "$bbuserinfo[securitytoken]";
var IMGDIR_MISC = "$stylevar[imgdir_misc]";
var vb_disable_ajax = parseInt("$vboptions[disable_ajax]", 10);
// -->
</script>

why use this codes? if we not use, what will do?