digraph cats {
  graph [engine=fdp];
  subgraph cluster_big_cats {
    "Lion" "Snow Leopard";
  };
  subgraph domestic_cats {
    cluster=true;
    "Siamese" "Persian";
  };
  subgraph cluster_domestic_cats {
    "SiameseA" "PersianA";
  };
  cluster_big_cats -> domestic_cats;
  cluster_big_cats -> cluster_domestic_cats;
}
