- Only `<a>` elements with a `href` attribute should be matched, since
HTML5 allows `<a>` elements to omit `href`:
> If the a element has no href attribute, then the element represents
> a placeholder for where a link might otherwise have been placed, if
> it had been relevant, consisting of just the element's contents.
- Elements with the `tabindex` attribute should be matched, but not
`tabindex=-1`, which means explicitly saying that the element should
_not_ be focusable.