code: func (e *Errors) List(p ...Priority) []Err {
  	if len(p) == 0 {
  		return e.err
  	}
  
  	// filter errors to given priorities
  	var l []Err
  	for _, e := range e.err {
  		for _, priority := range p {
  			if e.p == priority {
  				l = append(l, e)
  			}
  		}
  	}
  	return l
  }
docs: // List returns all errors of a given priority, if no priority is given all
  // errors are returned.