digraph Perl
{
graph [ rankdir="TB" ]
node [ shape="oval" ]
edge [ color="grey" ]
"dummy.prefix.node" [ color="invis" label="" ]

subgraph "cluster_1"
{
graph [ rankdir="TB" ]
node [ shape="oval" ]
edge [ color="grey" ]

"Small"
}
"dummy.prefix.node" -> "Small" [ label="" ]
}