code: func (na *NetAddress) Valid() bool {
  	return na.IP != nil && !(na.IP.IsUnspecified() || na.RFC3849() ||
  		na.IP.Equal(net.IPv4bcast))
  }
docs: // For IPv4 these are either a 0 or all bits set address. For IPv6 a zero
  // address or one that matches the RFC3849 documentation address format.