Core Animation is, rather strangely, not just a framework for animation, but also a higher-level abstraction of what we have learned with Core Graphics. A large part of this chapter will deal with the CALayer class and its subclasses. Drawing into Core Animation layers is often easier and quicker than dropping down to Core Graphics. Subclassing, or customizing, Cocoa's own views and controls is mostly done through their CALayer properties. But the really magical thing about these layers is the extent to which their properties are already primed for animation. If you can set it on a CALayer, chances are you can animate it, and, generally, animate it very easily.
Core Animation relieves us of the burden of thousands of lines of animation code, presenting us with abstractions that give us as much or as little control over animated user-interface elements as we are likely to need.