How to call an element of the "root" document from a nested html code?

How to call an element of the "root" document from a nested html code?

Hey!
I've a PHP page that imports a menu bar throught an external html code.

Something like this

Panel.php
  1. <?php include("sideMenu.html"); ?>
    <div id="proof"></div>

I want to place in sideMenu.html some jQuery code that can interact with the "proof" div.. How i can do that? I think that we can call Panel.php a "root" element, right?