Using the XML Parser is nearly identical to using the JSON Parser, and it serves much of the same purpose. Using these parsers accelerates the data collection process and allows you to do more at once.
Again, not every webpage uses XML requests, but using a parser when the page does greatly increases performance.
Open the activity monitor
Find the completed AJAX request with content resembling XML data in the AJAX Content column.
Example of a XML file:
<?xml version="1.0" encoding="UTF-8"?>
<body>Look at this cool text!</body>
Copy the URL from that AJAX request and paste it into the web browser URL bar. Click the blue arrow to load the page, then navigate over to the Agent Settings tab and Click the Web Browser dropdown in order to select XML parser.