gether.
    Items are filtered per group, and displayed as

    Group items can contain the properties <code>id</code>,
    <code>content</code>, and <code>className</code> (optional).
  </p>
  <p>
    Groups can be applied to a timeline using the method <code>setGroups</code> or supplied in the constructor.
    A table with groups can be created like:
  </p>

<pre class="prettyprint lang-js">
var groups = [
  {
    id: 1,
    content: 'Group 1'
    // Optional: a field 'className', 'style', 'order', [prope