E4X was an extension to ECMAScript which allowed for native handling of XML.
ECMAScript For XML (E4X) was an extension to ECMAScript which allowed use of XML literals, as well as accessors and filters for working with such XML. Its ability to allow embedding of JavaScript also was convenient for building XML-based templates.
Standardized in ECMA-357, it was supported in Mozilla's Spidermonkey and Rhino Javascript engines, and was included in the Firefox web browser between versions 1.5 and 20.
Warning: E4X is obsolete. It has been disabled by default for webpages (content) in Firefox 17, disabled by default for chrome in Firefox 20, and has been removed in Firefox 21. Use DOMParser/DOMSerializer or a non-native JXON algorithm instead.
More information can be found at https://developer.mozilla.org/en/e4x
