HTTP GET used for unsafe interactions (not good)

Modifying state of shopping cart is unsafe since produces side-effect:

"Add to Cart" an HTML link:

   <a href=".../AddToShoppingCart?docNumber=6,678,889...">...

I cannot link to shopping cart from this slide; a search engine or pre-fetching agent might increment counter (cf. SVG 1.2, section 11.8.

In HTML, use "POST" form for unsafe operations.