anchor.diff:  
     ## The road ahead
     You've expanded the Tour of Heroes app, but it's far from complete.
  -  You can't put the entire app into a single component.
  -  In the [next page](toh-pt3.html), you'll split the app into sub-components and make them work together.
  +  An app shouldn't be one monolithic component.
  +  In the [next page](toh-pt3.html), you'll split the app into subcomponents and make them work together.
  
positive.code:   :marked
      ### Hide the empty detail with ngIf
  
      When the app loads, the `selectedHero` is undefined and won't be defined until you click a hero's name.
      Angular can't display properties of the undefined `selectedHero` and throws the following error,
      visible in the browser's console:
  
  
negative.code: 
    ### List heroes with ngFor
  
    The goal is to bind the array of heroes in the component to the template, iterate over them,
    and display them individually.
  
    Modify the `<li>` tag by adding the built-in directive `*ngFor`.
  