sequence.go
func (s *FileSequence) FrameRange() string {
	if s.frameSet == nil {
		return ""
	}
	return s.frameSet.FrameRange()
}
func (s *FileSequence) FrameRange() string {
	if s.frameSet == nil {
		return ""
	}
	return s.frameSet.FrameRange()
}
// FrameRange returns the string frame range component,
// parsed from the sequence. If no frame range was parsed,
// then this method will return an empty string.