title: bokeh: adding details to a high level chart
body: <p>What is the simplest way to combine high level charts (like Bar) with something else (like a line)?</p>
  
  <pre><code>b = Bar(df)
  b.line(df.mean())
  </code></pre>
  
  <p>This won't work because <code>b</code> is not a figure.</p>
  
  <ol>
  <li>How can I get the figure handle from <code>b</code>? (and/or)</li>
  <li>How can I create the line and bar separately and then combine?</li>
  </ol>
  
  <p>(I'm trying to avoid making the bar manually using the lower level quad or rect.)</p>