Tracking https://groups.google.com/group/jquery-api-team/browse_thread/thread/2699cbd60063398b

Author: rdworth

entries/jQuery.ajax.xml

@@ -16,7 +16,7 @@
         <desc>The content type sent in the request header that tells the server what kind of response it will accept in return. If the <code>accepts</code> setting needs modification, it is recommended to do so once in the <code>$.ajaxSetup()</code> method.</desc>
       </option>
       <option default="true" name="async" type="Boolean">
-        <desc>By default, all requests are sent asynchronously (i.e. this is set to <code>true</code> by default). If you need synchronous requests, set this option to <code>false</code>. Cross-domain requests and <code>dataType: "jsonp"</code> requests do not support synchronous operation. Note that synchronous requests may temporarily lock the browser, disabling any actions while the request is active.</desc>
+        <desc>By default, all requests are sent asynchronously (i.e. this is set to <code>true</code> by default). If you need synchronous requests, set this option to <code>false</code>. Cross-domain requests and <code>dataType: "jsonp"</code> requests do not support synchronous operation. Note that synchronous requests may temporarily lock the browser, disabling any actions while the request is active. <strong>As of jQuery 1.8, the use of <code> async: false </code> is deprecated.</strong></desc>
       </option>
       <option name="beforeSend(jqXHR, settings)" type="Function">
         <desc>A pre-request callback function that can be used to modify the jqXHR (in jQuery 1.4.x, XMLHTTPRequest) object before it is sent. Use this to set custom headers, etc. The jqXHR and settings maps are passed as arguments. This is an <a href='http://docs.jquery.com/Ajax_Events'>Ajax Event</a>. Returning <code>false</code> in the <code>beforeSend</code> function will cancel the request. <strong>As of jQuery 1.5</strong>, the <code>beforeSend</code> option will be called regardless of the type of request.</desc>