title: change order of nodes in subgroup in graphviz
body: <p>In the following code:</p>
  
  <pre><code>digraph G { 
    splines=true;
  
    bpx_launch -&gt; bpx_preproc [color=red];
  
    subgraph cluster_0 {
      slice01;
      slice02;
      slice03;
      slice_i;
      slice_N;
      color=black;
    }
  
    bpx_launch -&gt; bpx_postproc [color=red];
    bpx_launch -&gt; bpx_validate [color=red];
    bpx_launch -&gt; slice01 [color=red];
    bpx_launch -&gt; slice02 [color=red];
    bpx_launch -&gt; slice03 [color=red];
    bpx_launch -&gt; slice_i [color=red];
    bpx_launch -&gt; slice_N [color=red];
  
    bpx_preproc -&gt; slice01 [color=blue];
    bpx_preproc -&gt; slice02 [color=blue];
    bpx_preproc -&gt; slice03 [color=blue];
    bpx_preproc -&gt; slice_i [color=blue];
    bpx_preproc -&gt; slice_N [color=blue];
  
    slice01 -&gt; bpx_postproc [color=blue];
    slice02 -&gt; bpx_postproc [color=blue];
    slice03 -&gt; bpx_postproc [color=blue];
    slice_i -&gt; bpx_postproc [color=blue];
    slice_N -&gt; bpx_postproc [color=blue];
  
    bpx_postproc -&gt; bpx_validate [color=blue];
  }
  </code></pre>
  
  <p>I end up getting <code>slice_N, slice01, slice02, slice03, slice_i</code>, but I would prefer <code>slice01, slice02, slice03, slice_i, slice_N</code>. Is there any way to change that order?</p>
  
  <p>Also, how do I add a key for arrows? I would like to show a little legend which explains that "x -> y" means "x launches y" for red and "x must run before y" for blue.</p>
  
  <p>EDIT: Mistakenly had the first 'bpx_launch' as 'bpx' so it didn't make sense - it should all read as 'bpx_launch' - there should be no node named 'bpx'</p>