From Seo Wiki - Search Engine Optimization and Programming Languages
xajax runs on any PHP 4.3.x and PHP 5.x Apache or IIS server.
xajax runs on (but is not limited to) Internet Explorer 6+, Firefox, Opera 8.0+, Safari 3.0.
Limitations of xajax
Currently, xajax has no way to transfer data from client to server other than using XML. There are plans to change xajax to allow programmers to use JSON or any other means of communication.
It is possible to send JSON using:
<?php $response->script('example ='.json_encode($example)); ?>