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1·QR code stands for quick response, a reference to how speedily the data they contain can be decoded.

QR是快速反应的意思，意指代码中的数据能够迅速解码。

2·Listing 9, a quick example from Ruby on Rails, shows a closure that is used to code the response of an HTTP request.

清单9是Ruby on Rails中的一个简短例子，清单中的闭包用于为一个HTTP请求编写响应代码。

3·Since this is critical code that you'll use in some form in every Ajax application you write, take a quick tour through what a basic request/response model with Ajax looks like.

因为这段代码非常重要，您编写的每个 Ajax 应用程序都要以某种形式使用它，先看看 Ajax 的基本请求/响应模型是什么样吧。