show customer email address

I'm trying to edit my checkout page to display the customer's email address (with an edit button, so they can change it if they typed it in wrong), but I can't figure out how.

Based on what create_account.php does with the original email address input, I thought the following would work, but it didn't:

echo ($_SESSION['customers_email_address']);

I've used the Developer's Tool Kit to look for clues, searched the forums hoping the question had come up before, and tried all sorts of variations I knew wouldn't work, but no luck.

I'm new to php and have not fully mastered the way it uses variables and arrays. Could someone please point me in the right direction? Thanks!

Never mind. On further examination I realized that the solution was to add

$_SESSION['customers_email_address'] = $email_address;

to create_account.php. There is a little cluster of $_SESSION variables set near the end, but an email address variable wasn't one of them because the program as written wasn't planning on calling for it.