docs: private AbstractPlanNode handleUnionLimitOperator(AbstractPlanNode root) {
          // The coordinator's top limit graph fragment for a MP plan.
          // If planning "order by ... limit", getNextUnionPlan()
          // will have already added an order by to the coordinator frag.
          // This is the only limit node in a SP plan
          LimitPlanNode topLimit = m_parsedUnion.getLimitNodeTop();
          assert(topLimit != null);
          return inlineLimitOperator(root, topLimit);
      }