I've noticed that I can use
<div id="a" class="b c"></div>
<script>a.innerHTML = a.classList</script>
The HTML5 standard specifies that the window object must have a property key whose value is elem if...
there is exactly one DOM element elem whose property id has the value key.
there is exactly one DOM element elem whose property name has the value key. elem’s tag must be one of: a, applet, area, embed, form, frame, frameset, iframe, img, object.