anchor.diff:  
   :marked
     ### Headers
  +
     ### 请求头(Headers)
   
     The `Content-Type` header allows us to inform the server that the body will represent JSON.
  
positive.code:     这样效率很低，而且在流量受限的移动设备上会显得过于昂贵。
  
      ### 1. Wait for the user to stop typing
      ### 1. 等用户停止输入
      At the moment we call the server after every key stroke.
      The app should only make requests when the user *stops typing* .
      Here's how it *should* work &mdash; and *will* work  &mdash;  when we're done refactoring:
      
      现在，我们会在每次按键之后调用服务器。
      但合理的方式是只在用户*停止输入*之后才发起请求。
      这是它*应该*而且*即将使用*的工作方式，我们马上就重构它：
    figure.image-display
      img(src='/resources/images/devguide/server-communication/wiki-2.gif' alt="Wikipedia search app (v.2)" width="250")
    :marked
      ### 2. Search when the search term changes
      ### 2. 当搜索关键字变化了才搜索
  
      Suppose the user enters the word *angular* in the search box and pauses for a while. 
  
negative.code: a#error-handling
  :marked
    ### Always handle errors
  
    ### 总是处理错误
  
    Whenever we deal with I/O we must be prepared for something to go wrong as it surely will. 
  