frameset.go
func (s *FrameSet) Invert() *FrameSet {
	ptr := s.rangePtr.Inverted()
	return &FrameSet{ptr.String(), ptr}
}
func (s *FrameSet) Invert() *FrameSet {
	ptr := s.rangePtr.Inverted()
	return &FrameSet{ptr.String(), ptr}
}
// Invert returns a new FrameSet that represents
// all frames *not* within the current FrameSet. That is, it
// will create a range that "fills in" the current one.