There's still a `data-id` attribute set - it just happens programmatically, to the template's container. That is:

~~~~
<li data-id="0">
  <div class="unplaced-unit"></div>
</li>
~~~~

Instead of:

~~~~
<li>
  <div data-id="0" class="unplaced-unit"></div>
</li>
~~~~

Having it on the container means one less layer in the DOM to dig down into.