Branch
graph ethane {}
digraph foo {}
subgraph bar {}
----------------------------------------------------
[
["keyword", "graph"],
["graph-name", ["ethane"]],
["punctuation", "{"],
["punctuation", "}"],
["keyword", "digraph"],
["graph-name", ["foo"]],
["punctuation", "{"],
["punctuation", "}"],
["keyword", "subgraph"],
["graph-name", ["bar"]],
["punctuation", "{"],
["punctuation", "}"]
]