title: How do I order subgraph clusters when using dot?
body: <p>I have a dot file in which I create subgraph clusters which I want to appear in a specific order, let's say I have this:</p>
  
  <pre><code>digraph G {
      splines=true;
      sep="+25,25";
      overlap=scalexy;
      nodesep=0.6;
      subgraph cluster_2 {
          label="ADD_MORE_PROBLEMS";
          subgraph cluster_3 {
              label="pattern";
              N1 [label="problem"];
          }
          subgraph cluster_4 {
              label="replacement";
              N2 [label="problem"];
              N3 [label="problem"];
          }
      }
  }
  </code></pre>
  
  <p>Which creates:</p>
  
  <p><a href="https://i.stack.imgur.com/CmqUh.png" rel="noreferrer"><img src="https://i.stack.imgur.com/CmqUh.png" alt="output from dot"></a></p>
  
  <p>How do I ensure that "pattern" appears to the left of "replacement" (I may have an arbitrary number of subgraphs).</p>