title: Transparent legend in Bokeh
body: <p>In Matplotlib the legend function has a keyword argument called fancybox that makes the legend slightly transparent to see the lines behind the legend. Here is an example function call:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  plt.legend(fontsize='xx-small', loc='best', fancybox=True)
  </code></pre>
  
  <p>I can't find anything similar to this in Bokeh. Does anyone know if Bokeh has the functionality to make a plot transparent without going behind the scenes and monkey patching something in for it? Thanks.</p>