strict digraph M {
    subgraph "cluster_Top" {
        label=<<b>Top</b>>
        style="filled"
        fillcolor="/blues5/1"
        "station0" [shape=box,style="rounded,filled",fillcolor="/blues5/2",label=<<b>station0..station2</b><br align="left"/>>];
        subgraph "cluster_tankerco" {
            label=<<b>tankerco</b>>
            style="filled"
            fillcolor="/blues5/2"
            "tankerco.truck0" [shape=box,style="rounded,filled",fillcolor="/blues5/3",label=<<b>truck0..truck1</b><br align="left"/>>];
        }
    }
}