title: D3 Bar Chart with Tooltip on X-Axis
body: <p>I am using a D3 bar chart.  I can show the tooltip when the mouse is over the bar (from <a href="http://bl.ocks.org/Caged/6476579" rel="nofollow">http://bl.ocks.org/Caged/6476579</a>).  However, in some of my charts, the Y range is large, with some having a large value and some small, with the result that some of the bar charts have essentially 0 height.  So, I might have points ('a', 10245), and ('b', 32).  That '32' is still important, but I can't mouse over the bar because it is too small.</p>
  
  <p>How can I add the same tooltip to the x-axis, so I can show a tip that says 'b:32'?   </p>