I have a set of
<label><input type="checkbox" value="a1"/>A1</label>
<label><input type="checkbox" value="a2"/>A2</label>
a? Because it should only be used for links to resources.
div? Because it isn’t focusable by default (for keyboard users), and because it doesn’t come with an implicit WAI-ARIA role (for accessibility), so you would have to add both features manually, essentially recreating an element that already exists: