digraph Perl
{
graph [ rankdir="TB" ]
node [ shape="oval" ]
edge [ color="grey" ]

subgraph "cluster.1"
{
graph [ rankdir="TB" ]
node [ shape="oval" ]
edge [ color="grey" ]

"node.1"
"node.2"
}
"node.1" -> "node.2" [ label="" ]
}