O.propertyIsEnumerable & setPropertyIsEnumerable

var arg:Object = new Object;
arg.a = "aa";
arg.b = "bb";
arg.c = "cc";
trace(arg.propertyIsEnumerable("a")); // true
arg.setPropertyIsEnumerable("a",false);
trace(arg.propertyIsEnumerable("a")); // false;
for(var index:String in arg){
  trace(index); // b, c
}