A preliminary study of Ajax technology

Ajax has been very interested in Gmail's client technology, today I found some Ajax resources, introduced as follows:
Ajax
Web Client Technology: Asynchronous JavaScript + XML
Mainly based on the following technologies:
standards-based presentation using XHTML and CSS;
Dynamic display and interaction using the Document Object Model;
Data interchange and manipulation using XML and XSLT;
Asynchronous data retrieval using XMLHttpRequest;
and JavaScript binding everything together.

Main Features:
Reflash without Reload
Reference:
O ' Reilly's xml.hacks and JavaScript: The Definitive Guide
goog_ajaxsl_v0.2 (can be found on the code.google.com, open source implementation)


Instance:
Http://map.google.com
Gmail (especially spell check)
http://sean.treadway.info/demo/upload/
http://www.broken-notebook.com/spell_checker/
The last one is PHP.

Ref_url:
Http://blog.yam.com/syshen/archives/184517.html
http://www.adaptivepath.com/publications/essays/archives/000385.php
Http://jacky.seezone.net/archives/001188.html<