Save as FXG option not working from script. Am I doing this right?

I see that the Illustrator Scripting reference document for CC 2014 [1] has references to FXG, FXGSaveOptions, etc.  I thought I would give it a try to see if I can save a document to FXG.  Here is what I am trying:

var myDocument = app.documents[0];
var myTextFrame = myDocument.textFrames.add();
myTextFrame.position = [200,200];
myTextFrame.contents = "Hello World!"

var newFile = new File("c:/temp/fxgfile");
var fxgSaveOptions = new FXGSaveOptions();
myDocument.save(newFile,fxgSaveOptions);

This causes the file to get saved as fxgfile.ai and not fxgfile.fxg that I was looking for.

Any ideas?

Thanks,

Om

[1] http://wwwimages.adobe.com/content/dam/Adobe/en/devnet/illustrator/sdk/CC2014/Illustrator% 20Scripting%20Reference%20-%20…