ADC Article: http://developer.apple.com/internet/webcontent/xmlhttpreq.html

Basically, it allows your client to asynchronously connect to the server and retrieve XML or HTML documents, returning the results in XML for parsing. Should allow some interesting remote scripting applications, but i’m not sure that it’s 100% cross browser compatible. According to the article, look for this to get picked up as a de facto standard.

Also has interesting example (I think it can be played in Safari, Moz, and IE 5+ so far. http://developer.apple.com/internet/webcontent/XMLHttpRequestExample/example.html