code: func (s *UpdateByQueryService) WaitForActiveShards(waitForActiveShards string) *UpdateByQueryService {
  	s.waitForActiveShards = waitForActiveShards
  	return s
  }
docs: // WaitForActiveShards sets the number of shard copies that must be active before proceeding
  // with the update by query operation. Defaults to 1, meaning the primary shard only.
  // Set to `all` for all shard copies, otherwise set to any non-negative value less than or equal
  // to the total number of copies for the shard (number of replicas + 1).