anchor.diff:    It modifies the behavior of an existing element (typically an `<input>`) 
     by setting its display value property and responding to change events.
     
  -  Angular ships with a small number of other directives that either alter the layout structure 
  +  Angular ships with a few other directives that either alter the layout structure 
     (e.g. [ngSwitch](template-syntax.html#ngSwitch))
     or modify aspects of DOM elements and components 
     (e.g. [ngStyle](template-syntax.html#ngStyle) and [ngClass](template-syntax.html#ngClass)).
  
positive.code:   Some modules are libraries of other modules.
    
    Angular itself ships as a collection of library modules called "barrels". 
    Each Angular library is actually a public facade over several logically related private modules.
    
    The `angular2/core` library is the primary Angular library module from which we get most of what we need.
    <br clear="all">
  
negative.code:     While we're focused on our application, *import* and *export*
      is about all we need to know.
  :marked
    The key take-aways are:
    * Angular apps are composed of modules.
    * Modules export things &mdash; classes, function, values &mdash; that other modules import.
    * We prefer to write our application as a collection of modules, each module exporting one thing.
  