title: How to annotate nodes and edges with Graphviz?
body: <p>How can I draw a graph with Graphviz and annotate its nodes and edges?</p>
  
  <p>For example:</p>
  
  <pre><code>(a: level=0) --3--&gt; (b: level=1)  
  (a: level=0) --2--&gt; (c: level=1)
  </code></pre>