有目的的动效

Exposure frequency sets an animation's acceptable emphasis and length; repeated motion benefits from greater restraint.

用户看到一段动画的频率越高，它就应越短、越克制。

Objects retain coherent position, direction, and identity across states so changes remain easy to trace.

让元素在不同状态之间保持身份与空间位置的连续，使用户始终知道内容去了哪里。