code: func (e *Errors) Append(err *Errors) error {
  	if err == nil {
  		return nil
  	}
  
  	e.m.Lock()
  
  	// append Errors at the end of the current list
  	e.err = append(e.err, err.err...)
  
  	// set highest priority
  	if err.p > e.p {
  		e.p = err.p
  	}
  
  	e.m.Unlock()
  	return nil
  }
docs: // Append add all Errors to existing Errors