code: func (a *ErrorList) AppendWithPrefix(err error, prefix string) {
  	switch err := err.(type) {
  	case ErrorList:
  		for i := range err {
  			*a = append(*a, fmt.Errorf("%s%s", prefix, err[i]))
  		}
  	default:
  		*a = append(*a, fmt.Errorf("%s%s", prefix, err))
  	}
  }
docs: // AppendWithPrefix appends an error to the list and includes a prefix.