transition-timing-function

CSS属性受到 transition effect的影响，会产生不断变化的中间值，而 CSS transition-timing-function 属性用来描述这个中间值是怎样计算的。实质上，通过这个函数会建立一条加速度曲线，因此在整个transition变化过程中，变化速度可以不断改变。

这条加速度曲线被<timing-function> (en-US)所定义，之后作用到每个CSS属性的过渡. 

你可以规定多个timing function,通过使用 transition-property属性，可以根据主列表(transition property的列表)给每个CSS属性应用相应的timing function.如果timing function的个数比主列表中数量少，缺少的值被设置为初始值（ease） 。如果timing function比主列表要多，timing function函数列表会被截断至合适的大小。这两种情况下声明的CSS属性都是有效的。

Formal syntax: 
<easing-function>#
where 
<easing-function> = linear | <cubic-bezier-timing-function> | <step-timing-function>
where 
<cubic-bezier-timing-function> = ease | ease-in | ease-out | ease-in-out | cubic-bezier(<number [0,1]>, <number>, <number [0,1]>, <number>)
<step-timing-function> = step-start | step-end | steps(<integer>[, <step-position>]?)
where 
<step-position> = jump-start | jump-end | jump-none | jump-both | start | end

transition-timing-function: ease
transition-timing-function: ease-in
transition-timing-function: ease-out
transition-timing-function: ease-in-out
transition-timing-function: linear
transition-timing-function: cubic-bezier(0.1, 0.7, 1.0, 0.1)
transition-timing-function: step-start
transition-timing-function: step-end
transition-timing-function: steps(4, end)

transition-timing-function: ease, step-start, cubic-bezier(0.1, 0.7, 1.0, 0.1)

transition-timing-function: inherit

<timing-function>

通过transition-property中定义被过渡属性，每个 <timing-function> (en-US)的值代表与这个属性相对应的timing function.

• Using CSS transitions
• TransitionEvent