docs: protected boolean atBoundary( PlanNode criteriaNode,
                                    PlanNode originatingNode ) {
          // Walk from source node to critNode to check each intervening node
          PlanNode currentNode = originatingNode.getParent();
          while (currentNode != criteriaNode) {
              if (currentNode.getType() != Type.SELECT) return false;
              currentNode = currentNode.getParent();
          }
          return true;
      }