What will be the result of calling the save() method on a collection instance?

In layout files you can change al element's order on a page. This can be done using one of the following:
<move> instruction
before and after element attributes?
How are two methods different?

Assume that a customer's cart only includes one downloadable product.
What effect will it cause on the quote object?

What are two functions of a resource model? (Choose two.)

In a code review of a merchant's site you have discovered that there are multiple observers for the checkout_submit_all_after event. After closer inspection, you notice one of these observers is relying on the others being executed before it is called.
What risk does this pose, and how can it be mitigated?