code: func (s *Subnet) Contains(a Address) bool {
  	if len(a) != len(s.address) {
  		return false
  	}
  	for i := 0; i < len(a); i++ {
  		if a[i]&s.mask[i] != s.address[i] {
  			return false
  		}
  	}
  	return true
  }
docs: // Contains returns true iff the address is of the same length and matches the
  // subnet address and mask.