php - How to find a smarty variable where was called in prestashop 1.6 -

i learning prestashop, example want modify delivery pdf format. in delivery-slip.tpl file:

 <td colspan="12">     {$product_tab}   </td> 

how can located {$product_tab} injected? thanks

hey {$product_tab} variable coming controller of delivery-slip "deliveryslipcontroller.php" in controllers folder.