Using XML in Ajax (with PHP)

In support of my earlier post about using the XMLHttpRequest object for XML, here is a nice article demonstrating the use of the responseXML attribute of the XMLHttpRequest with PHP. Here is another.

Also, just for reference here are a few nice sites discussing developments in AJAX:
Ajaxian
AJAX blog
AJAX Matters
ajax info

As well as some good usage guideline articles:
Ajax Mistakes
XMLHttpRequest Usability Guidelines