code: func unchanged(nf, ef FileIntf) bool {
  	return ef.FileVersion().Equal(nf.FileVersion()) && ef.IsInvalid() == nf.IsInvalid()
  }
docs: // unchanged checks if two files are the same and thus don't need to be updated.
  // Local flags or the invalid bit might change without the version
  // being bumped. The IsInvalid() method handles both.