Why cant I access $_SESSION[USERID]?

When i embed an html page in an iframe on a .tpl file, can I access smarty session variables such as $_SESSION[USERID]? I am trying to figure out why I cant get a userID because I am doing it the same way I have done it before. Are there any restrictions of javascript or json enco开发者_如何学编程ding on $_SESSION[USERID]?

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use session_start() at the top of the page where u want to retrieve the $_SESSION variable

i think in smarty you can get the session data like this

$smarty.session.USERID