Viz/graphviz.org+doc+info+attrs.html

graph G {
  B \-\- A [taillabel = "tail"]
}

digraph G {
 graph [class="cats"];

 subgraph cluster_big {
   graph [class="big_cats"];

   "Lion" [class="yellow social"];
   "Snow Leopard" [class="white solitary"];
 }
}

digraph G {

 a -> b [dir=both color="red:blue"]
 c -> d [dir=none color="green:red;0.25:blue"]

}

digraph G {

 a -> c;
 a -> b;
 b -> c [constraint=false];

}