You used to need to do different things for AJAX depending on browser version. My guess is that's what they're referring to. For example, older versions of Inte

You used to need to do different things for AJAX depending on browser version. My guess is that's what they're referring to. For example, older versions of Internet Explorer used "ActiveXObject("Microsoft.XMLHTTP")" instead of "XMLHttpRequest". See: http://www.w3schools.com/ajax/ajax_xmlhttprequest_create.asp http://www.w3schools.com/ajax/ajax_xmlhttprequest_create.asp