notes.txt

http://www.graphviz.org/content/dot-language

X graph   :   [ *strict* ] (*graph* | *digraph*) [ ID ] '{' stmt_list '}'
X stmt_list   :   [ stmt [ ';' ] [ stmt_list ] ]
X stmt   :   
X          node_stmt
X      |   edge_stmt
X      |   attr_stmt
X      |   ID '=' ID
X      |   subgraph
X attr_stmt   :   (*graph* | *node* | *edge*) attr_list
X attr_list   :   '[' [ a_list ] ']' [ attr_list ]
X a_list   :   ID [ '=' ID ] [ ',' ] [ a_list ]
X edge_stmt   :   (node_id | subgraph) edgeRHS [ attr_list ]
X edgeRHS   :   edgeop (node_id | subgraph) [ edgeRHS ]
X edgeop : '->' | '--'
X node_stmt   :   node_id [ attr_list ]
X node_id   :   ID [ port ]
X port   :   ':' ID [ ':' compass_pt ] 
          |  ':' compass_pt
X subgraph   :   [ *subgraph* [ ID ] ] '{' stmt_list '}'
X compass_pt   :   (n | ne | e | se | s | sw | w | nw | c | _)