Events and Objects
We can't look at dragging layers without including events and objects. You may already understand these concepts (from Chapter 10), but I'll include a brief review just in case.
Events
Events are things that happen that the browser can detect. For example, the page loading, the user pressing a mouse button, moving the mouse, and releasing a button are all events. Fortunately, the browser doesn't just notice that these events occur—the browser also sees exactly where the events occurred. For example, if the user clicks somewhere on a screen, JavaScript is not only aware that the click occurred, but also knows where on the screen it happened.
We'll be looking at only three events in this chapter:
mousedown: The user presses ...
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