@Override
 public JsonGenerator disable(Feature f) {
   _features &= ~f.getMask();
   if (f == Feature.WRITE_NUMBERS_AS_STRINGS) {
     _cfgNumbersAsStrings = false;
   }
   return this;
 }
 @Override
 public final boolean isEnabled(Feature f) {
   return (_features & f.getMask()) != 0;
 }