E4X is an extension to JavaScript that is available to both Firefox and ActionScript developers that turns XML into a native data type on par with strings, arrays, objects, and regular expressions. It is not a DOM representation of XML, but rather is its own distinct entity, something that has its own set of associated methods and operators and that is intended to making it easier to work with XML than using the sometimes cumbersome methods associated with DOM (perhaps the closest analogy I can think of would be the comparison between modeling clay with your bare hands and modeling clay with a waldo while wearing a space suit).