Reinstate para about XHR

files/en-us/web/api/fetch_api/using_fetch/index.md

@@ -8,6 +8,8 @@ page-type: guide
 
 The [Fetch API](/en-US/docs/Web/API/Fetch_API) provides a JavaScript interface for making HTTP requests and processing the responses.
 
+Fetch is the modern replacement {{domxref("XMLHttpRequest")}}: unlike `XMLHttpRequest`, which uses callbacks, Fetch is promise-based and is integrated with features of the modern web such as [service workers](/en-US/docs/Web/API/Service_Worker_API) and [Cross-Origin Resource Sharing (CORS)](/en-US/docs/Web/HTTP/CORS).
+
 With the Fetch API, you make a request by calling {{domxref("fetch()")}}, which is available as a global function in both {{domxref("Window", "window", "", "", "nocode")}} and {{domxref("WorkerGlobalScope", "worker", "", "", "nocode")}} contexts. You pass it a {{domxref("Request")}} object or a string containing the URL to fetch, along with an optional argument to configure the request.
 
 The `fetch()` function returns a {{jsxref("Promise")}} which is fulfilled with a {{domxref("Response")}} object representing the server's response. You can then check the request status and extract the body of the response in various formats, including text and JSON, by calling the appropriate method on the response.