javascript - Using sortable.js with html5 custom data attribute

Question

How does one use html5's custom data attribute to sort items using sortable.js. Or how does one define custom sorting parameter using sortable.js

For example in the code below, I'd like to sort with data-timestamp

<ul id="items">
    <li data-timestamp='1'>item Y</li>
    <li data-timestamp='2'>item B</li>
    <li data-timestamp='3'>item Z</li>
</ul>