This version, developed under the working name of ECMAScript 3.1, will be known as ECMAScript, Fifth Edition, and will supercede the current formally established standard, ECMAScript, Third Edition. ECMAScript, Fourth Edition was never completed, but - according to the ECMA - much of the work done on it has been carried into the Fifth Edition.
The Fourth Edition (ES4) was scuttled in part due to objections by Microsoft, which arm-wrestled with Adobe and Mozilla over a number of the Fourth Edition's capabilities.
The debate over ES4 turned at times acrimonious, with Microsoft IE architect Chris Wilson saying that it introduced too many changes and Mozilla architect Brendan Eich accusing Wilson of spreading "falsehoods" about the proposed standard.
In the end, Microsoft won - with the ultimate result being the newly released final draft of the Fifth Edition.
According to an ECMA statement, the Fifth Edition contains a number of specs that are now common in major browsers, including features that have emerged since the Third Edition was formalized such as "accessor properties, reflective creation and inspection of objects, program control of property attributes, additional array manipulation functions, support for the JSON object encoding format, and a strict mode that provides enhanced error checking and program security."
If final interoperability and compatibility testing goes as planned, the ECMA General Assembly should ratify the Fifth Edition by the end of this year. ®