In Chapter 2, "The Request," we started to discuss the response when we covered the ready state and status codes of the XHR. This chapter will go beyond this state of the request and focus on two specific data-interchange formats in which the response can be received. An Ajax response can come in various formats; the most common include JSON and the most widely accepted, XML. Each format can be useful depending on the results you are trying to achieve. However, deciding on a single format for your application can be useful as a convention for future management, especially if you are building a large-scale application. For example, if you decide to use XML as the response in one situation, it would be much easier to continue to count on that format as the response when making all other requests. This might differ from one application to the next but, if possible, it is an important theory to keep in mind. It is also good to keep in mind the scalability of the technology that you choose, especially if you are planning on creating a scalable application in which you expect exponential growth. Let's get started by taking an in-depth look at XML, the syntax, how to parse it, and how to use it in your next application.