What is the difference between online and offline shipping methods?

You added a new constructor argument to an existing action controller class.
When you reload the page you get a PHP error that the wrong argument is passed to the class.
How do you fix this?

How does Magento store customer address attribute values?

You are working on a Magento store which will be selling in two countries. Each country has its own set of payment methods.
How do you organize the project to support this requirement?

There are two different configurable products which both share one variation. The shared variation is represented by the same simple product.
A customer added both configurables to the cart with the same selected variation?
How will they be displayed?