code: func Parse(config *Config) (Interface, error) {
  	switch config.Mechanism {
  	case "any":
  		return any(config), nil
  	case "upnp":
  		return uPnP(config), nil
  	case "pmp":
  		return pmp(), nil
  	default:
  		return nil, ErrBadMechanism
  	}
  }
docs: // Parse parses a NAT interface description.