 click event.</li>
          <li><code>x</code> (Number): relative horizontal position of the click event.</li>
          <li><code>y</code> (Number): relative vertical position of the click event.</li>
          <li><code>time</code> (Date): Date of the clicked event.</li>
          <li><code>snappedTime</code> (Date): Date of the clicked event, snapped to a nice value.</li>
          <li><code>what</code> (String or null): name of the clicked thing: <code>item</code>, <code>background</code>, <code>axis</