anchor.diff:    the component's behavior continues.
     It remains attached to its DOM element. It continues to listen to events.
     Angular keeps checking for changes that could affect data bindings.
  -  Whatever the component was doing it keeps doing.
  -
  -  Although invisible, the component &mdash; and all of its descendent components &mdash;
  +  Whatever the component was doing, it keeps doing it.
  +
  +  Although invisible, the component &mdash; and all of its descendant components &mdash;
     tie up resources that might be more useful elsewhere.
     The performance and memory burden can be substantial and the user may not benefit at all.
   
  
positive.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 to look at how Angular
    manipulates the DOM and how we can do it ourselves in our own directives.
  
    In this chapter we will
  
negative.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 to see it again for a long time, if ever.
    The `ngIf` would be preferred in that case.
  
  <a id="template"></a>
  