code: func (s *IndicesOpenService) WaitForActiveShards(waitForActiveShards string) *IndicesOpenService {
  	s.waitForActiveShards = waitForActiveShards
  	return s
  }
docs: // WaitForActiveShards specifies the number of shards that must be allocated
  // before the Open operation returns. Valid values are "all" or an integer
  // between 0 and number_of_replicas+1 (default: 0)