How do sessions work in MODx

<?php
//snippet for code shop class instance

//Session variable
session_start();

//online db info ---------------
include("common.php");  // db constants
include_once("functions.php");  //generic functions
include_once("instance.shop.php");  //-connects to database creates array (used in next snippet) and disconnects
?>


<?php
//snippet for display in template
echo '<strong>View Your Order</strong>';

echo "<strong>(Value : ";
echo "\$".number_format($ordercontents['finaltotalprice'], 2); 
echo "</strong>";

echo "<strong>";
echo '/ Items : '.$orderitemcount .' )';
echo "</strong>";
?>

[QE_linksShown] => 1
    [QE_position] => 0/0
    [SN4786bb48e0f79] => e980bca706fdac0437c1013a38e7f788
    [cartID] => e980bca706fdac0437c1013a38e7f788
    [dbx-postmeta] => grabit:0 |1-|2-|3-|4-|5-&advancedstuff:0-|1-|2-
    [PHPSESSID] => 52ef22e3c14fc1d76e892ffd12ceec4f
    [exp_perpage] => 50
    [etomite_etomite_] => %5D%EC%03%F6%E4
    [exp_save_info] => no
    [exp_last_activity] => 1200573392
    [exp_last_visit] => 1200526063
    [bar] => shown
    [SESS63542523f88c858e362651fd3aea05e9] => qvpgfv8bhv1jfjgugi1mmb0eh2
    [exp_notify_me] => yes
    [style] => Trend
    [exp_mode] => normal
    [toggle_articles_detail] => 1
    [webfxtab_resourcesPane] => 3

function getCartID(){
			
	if(isset($_COOKIE["cartID"])){
		//unset($_COOKIE["cartID"]);
		return $_COOKIE["cartID"];
	}
	else{
		// There is no cookie set. We will set the cookie
		// and return the value of the users session ID for use with the cart
				
		setcookie("cartID", $_COOKIE["PHPSESSID"], time() + 14400); //set how long cookie should last
		return $_COOKIE["PHPSESSID"]; 
	}
}