Animation keyframes go beyond a simple transition to a more intricate animation that goes through one or more intermediate styles when transitioning between two sets of styles.
通过定义动画的关键帧，可以把两组样式之间的简单转场，升级成一种更复杂的动画，它会在转场期间经历一个或多个中间样式。
The * ("wildcard") state matches any animation state. This is useful for defining styles and transitions that apply regardless of which state the animation is in. For example.
（通配符）状态匹配任何动画状态。当定义那些不需要管当前处于什么状态的样式及转场时，这很有用。比如。
The fourth chapter analysize the major styles of traditional animation.
第四章论述传统动画的主要样式。
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