code: func (mf *MultiFlag) PrintHelp() error {
  	descriptors := make(optionDescriptorSlice, len(mf.Options))
  	for idx, opt := range mf.Options {
  		descriptors[idx] = opt.Descriptor()
  	}
  	sort.Sort(descriptors)
  
  	fmt.Fprintln(mf.Output, mf.Description)
  	return writeAlignedOptionDescriptors(mf.Output, []*OptionDescriptor(descriptors))
  }
docs: // PrintHelp prints a formatted help string for a MultiFlag. This help string
  // details the Options registered with the MultiFlag.