anchor.diff:  
   block promises
     h2#promises Fall back to Promises
  +
     h2#promises 倒退为承诺(Promise)
     :marked
       Although the Angular `http` client API returns an `Observable<Response>` we can turn it into a 
  
positive.code:   [HTTP](https://tools.ietf.org/html/rfc2616) is the primary protocol for browser/server communication.
    
    [HTTP](https://tools.ietf.org/html/rfc2616)是浏览器和服务器之间通讯的主要协议。
  .l-sub-section
    :marked
      The [`WebSocket`](https://tools.ietf.org/html/rfc6455) protocol is another important communication technology;
  
negative.code:     搜索关键词仍然是“angular”。这时应用程序不应该发起另一个请求。
  
      ### 3. Cope with out-of-order responses
  
      ### 3. 对付乱序响应体
  
      The user enters *angular*, pauses, clears the search box, and enters *http*. 
  