code: func (m *MultiError) Error() string {
  	m.mutex.Lock()
  	defer m.mutex.Unlock()
  
  	formattedError := make([]string, len(m.errs))
  	for i, e := range m.errs {
  		formattedError[i] = e.Error()
  	}
  
  	return strings.Join(formattedError, ", ")
  }
docs: // Error implements error interface.