code: func (f FlagInfo) BindTransformingStringFlag(flags *pflag.FlagSet, target *string, transformer func(string) (string, error)) FlagInfo {
  	// you can't register a flag without a long name
  	if len(f.LongName) > 0 {
  		flags.VarP(newTransformingStringValue(f.Default, target, transformer), f.LongName, f.ShortName, f.Description)
  	}
  	return f
  }
docs: // BindTransformingStringFlag binds the flag based on the provided info.  If LongName == "", nothing is registered