code: func (s *GitScanner) ScanRef(ref string, cb GitScannerFoundPointer) error {
  	callback, err := firstGitScannerCallback(cb, s.FoundPointer)
  	if err != nil {
  		return err
  	}
  
  	opts := s.opts(ScanRefsMode)
  	opts.SkipDeletedBlobs = true
  	return scanLeftRightToChan(s, callback, ref, "", opts)
  }
docs: // ScanRef scans through all objects in the current ref, excluding git objects
  // that have been modified or deleted before the ref.