anchor.diff:  :marked
     ### NgFor
   
  -  ### NgFor
  -
     `NgFor` is a _repeater_ directive &mdash; a way to customize data display.
   
     `NgFor`是一个_重复器_指令 —— 自定义数据显示的一种方式。
  
positive.code: :marked
    ### NgClass
  
    ### NgClass
  
    We typically control how elements appear
    by adding and removing CSS classes dynamically.
    We can bind to `NgClass` to add or remove several classes simultaneously.
  
negative.code:     要学习更多的*类似 index* 的值，例如`last`、`even`和`odd`，请参阅 [NgFor API 参考](../api/common/index/NgFor-directive.html)。
  
  :marked
    #### NgForTrackBy
  
    The `ngFor` directive has the potential to perform poorly, especially with large lists.
  