code: func newFlagTracker(flagger Flagger) *flagTracker {
  	fTr := &flagTracker{
  		flagger: flagger,
  		shorts: map[rune]struct{}{
  			'h': {}, // "h" is always used for help, so we can't set it.
  		},
  	}
  	fTr.pflagger, fTr.pflag = flagger.(PFlagger)
  	return fTr
  }
docs: // newFlagTracker sets up a flagTracker based on a flagger.