Technical References - [cart]
Putting [cart] in your template automatically creates a unique shopping cart
Putting [cart] in your template automatically creates a unique shopping cart that can be used in eCommerce. You must continue to pass the [cart] value from page to page (or store it in a cookie for retrieval) in order to continue writing and modifying the shopping order (using tags such as [addlineitem] and [setheader]). If no cart value is specified when the customer lands on a new page with a [cart] tag, then a new unique value is created displaying an empty cart, and you will lose contact with the previously created cart. ([cart] will never display in its literal raw form, unless WebDNA processing is turned off altogether.)
The cart is a simple tab-delimited text file with the cart number for its name (no file extension) that you can open on the server and inspect in a text editor. To understand the fieldnames and structure, see the entry for order file.
The cart value is a long number derived from the current time. For this reason, [cart] is also handy for generating a guaranteed-unique value somewhere, such as a record identifier or product SKU.