In the processing function, you get a pointer to the YYLTYPE structure holding the location, and you can generate a nice error message.

That's certainly effective, but I've found that if teams do a good job using metrics for a continuous review, holding the 20% review for each major system function is sufficient.

In most cases designers limit the shopping cart to its primary function - to stand for the virtual holding place for any products a customer selects from the online store.