anchor.diff:  
   - var rejected_promise = _docsFor == 'dart' ? 'propagated exception' : 'rejected promise';
   :marked
  -  In this demo service, you log the error to the console; in real life,
  +  This demo service logs the error to the console; in real life,
     you would handle the error in code. For a demo, this works.
   
     The code also includes an error to
  
positive.code:   Each hero in the heroes view should have a delete button.
  
    Add the following button element to the heroes component HTML, after the hero
    name in the repeated `<li>` tag.
  
  +makeExcerpt('src/app/heroes.component.html', 'delete', '')
  
  
negative.code: .l-main-section
  :marked
    ## Simulate the web API
  
    Until you have a web server that can handle requests for hero data,
    the HTTP client will fetch and save data from
    a mock service, the *in-memory web API*.
  
    Update <span ngio-ex>!{_appModuleTsVsMainTs}</span> with this version, which uses the mock service:
  
  