XML (Extensible Markup Language) is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards.
Which is better and why?
I can see where a site that works 100% in AJAX might optimize a bit better, due to not having to reload the page on each click.
But I am a huge fan of the big submit button ...