anchor.diff:    #### Reusability
     We refactor, rename, and relocate files as our application evolves.
     We can't do any of those things while the file calls `bootstrap`.
  -  we can't move it. 
  +  We can't move it. 
     We can't reuse the component in another application. 
     We can't pre-render the component on the server for better performance.
     
  
positive.code:   `AppComponent` in a visual tree. 
    A more sophisticated app would have more files and modules, at least as many as it had components.
    
    Quickstart isn't sophisticated; one component is all we need.
    Yet modules play a fundamental organizational role in even this small app.
    
    Modules rely on other modules. In TypeScript Angular apps, when we need something
  
negative.code: :marked
    ## Appendices
    The balance of this chapter is a set of appendices that
    elaborate on some of the points we covered quickly above.
    
    There is no essential material here. Continued reading is for the curious.
    
  