13.1. Taking a good look at drag and drop

Before drag and drop can take place, the computer must decide what can and can’t be dragged and what can or can’t be dropped upon. For instance, icons on your desktop can generally be dragged around, but other items, such as the clock on your task-bar (Windows) or menu bar (OS X) can’t. This level of control is necessary to allow the enforcement of certain workflows, as we’ll discuss in a bit.

In order to really understand drag and drop, we need to discuss the entire workflow. We’ll do this by dividing the workflow into what I like to call the drag-and-drop lifecycle, which can be broken up into three major categories: start of drag, the drag operation, and drop.