https://www.interspire.com/forum/showthread.php?t=14923
... I was looking at how easy it would be to update it to be 6.1.1 compatible...


Whilst the changes to template module calls in the PHP file and template TWIG tags were easily resolved it became clear that the whole discount module had been rewritten to use the QUOTE class that came into being in 6.x or possibly a little earlier.
Looking through the code a few key things have changed so I'm brain dumping them here so I can refer back and try to rewrite this thing properly.
1. $GLOBALS['ISC_CLASS_CART']->api->SetArrayPush('DISCOUNT_MESSAGES' calls now seem to be handled by this array $this->banners[] in tandem with 'DiscountMessage' and 'DiscountMessagePlural' and probably a few other labels.
2. $GLOBALS['ISC_CLASS_CART']->api calls are now primarily replaced with $quote (ISC_QUOTE class) calls.
Naturally enough the function names aren't directly translatable and the use of other modules like the TAX class means some of the variables being passed previously are redundant.