code: func LevelBarNewForInterval(min_value, max_value float64) (*LevelBar, error) {
  	c := C.gtk_level_bar_new_for_interval(C.gdouble(min_value), C.gdouble(max_value))
  	if c == nil {
  		return nil, nilPtrErr
  	}
  	return wrapLevelBar(glib.Take(unsafe.Pointer(c))), nil
  }
docs: // LevelBarNewForInterval() is a wrapper around gtk_level_bar_new_for_interval().