Which Edition of ECMA-262 Does Google Apps Script Support? -

According to the old Google Groups, Apps Script is based on ECMA-262 version 3.

It will be supported by the fact that the Autocomplete Third Edition array works in the editor.

Although the following code runs perfectly well, which doubts this:

  var array = [1,2,3,4,5 ]; Logger.log ("foreach:"); Array.for each (function (item, idx, arr) {logger.log (item);});   
 Note the use of the Ere function for the ECMA-262 5V version. <.  
 Can an official mind give a definitive answer on why this is the case? And is it safe to rely on all 5th edition features or a sub-set, which has been implemented and works?   
 
 
 (June 2013) says that the application provides a subset of the script and is based on it .  
  Edit:  Google has come back somewhat by November 2013, they are reporting that the application is based on script 1.6, with a reduction of 1.7 and 1.8 is.