I have product like Greeting Cards. In which there is an option to add user defined printed message in card with extra charges. How to modify the ProductForm without changing original file to add TextareaField on product page? In that field user can add message and then will proceed to "Add to cart".
Edit: I'm using Swipestripe Ecommerce module. But don't know the inner functionality perfectly as I'm new to it. It call ProductForm.php file by $ProductForm on Product.ss template. This form has a "select list box" of Variation. "Quantity" input field and "Add To Cart" button. I need to add "Message" Textarea input field after "select list box".