<p>New Products:</p>
<ul>
  <li><data value="398">Mini Ketchup</data></li>
  <li><data value="399">Jumbo Ketchup</data></li>
  <li><data value="400">Mega Jumbo Ketchup</data></li>
</ul>

data:hover::after {
  content: ' (ID ' attr(value) ')';
  font-size: 0.7em;
}