Where are the variables for 'addtocart_form.tpl.php' defined?

Question

I would like to specifically know where the variables $product_parent_id and $product_id are coming from.

I have created a second file titled addtocart_form2.tpl.php and would like for it to read from a second set of variables (i.e. $product_parent_id2, $product_id2) I have gone to shop.product_details.php and created the variable $product_id2 as pretty much a second instance of $product_id, but updated accordingly in its own set of database variables (if that makes any sense).

I just want to know where these variables are defined so I can alter the sources.

list($html,$children) = $ps_product_attribute->list_attribute( ( $product_parent_id > 0 )  ? $product_parent_id : $product_id );

Answer 1

$product_id and $product_parent_id are also in shop.product_details.php

line 35:

$product_id = intval( vmGet($_REQUEST, "product_id", null) );

line 78:

$product_parent_id = (int)$db_product->f("product_parent_id");

(in VM 1.1.9)