anchor.diff:  :marked
     ## NgIf Case Study
   
  -  Let’s focus on `ngIf`. It's a great example of a structural
  +  Let's focus on `ngIf`. It's a great example of a structural
     directive: it takes a boolean and makes an entire chunk of DOM appear
     or disappear.
   
  
positive.code:   a heavy price to create and destroy it.
  
    If we really expected to "wink" the component like this, toggling visibility would be the better choice.
    In most UIs, when we "close" a component we're unlikely see it again for a long time, if ever.
    The `ngIf` would be preferred in that case.
  
  <a id="template"></a>
  
negative.code:   One of the defining features of a single page application is its manipulation
    of the DOM tree. Instead of serving a whole new page every time a user
    navigates, whole sections of the DOM appear and disappear according
    to the application state. In this chapter we'll look at how Angular
    manipulates the DOM and how we can do it ourselves in our own directives.
  
    In this chapter we will
  