app.activeDocument.xmlElements.firstItem().xmlElements.everyItem().untag();  
var root_tag = app.activeDocument.xmlElements.firstItem().markupTag; 
for (var i = app.activeDocument.xmlTags.length-1; i >= 0; i--) 
{ 
	if (app.activeDocument.xmlTags.item(i) != root_tag) 
		app.activeDocument.xmlTags.item(i).remove(root_tag); 
}