- https://html.spec.whatwg.org/multipage/interaction.html#focus
- https://www.w3.org/TR/2016/REC-html51-20161101/editing.html#can-be-focused
- https://www.oreilly.com/ideas/proposing-css-input-modality
- https://www.sitepoint.com/learning-to-focus/
- https://egghead.io/lessons/css-focus-management-using-css-html-and-javascript
- https://youtu.be/ilj2P5-5CjI?list=PLNYkxOF6rcICWx0C9LVWWVqvHlYJyqw7g
- https://drafts.csswg.org/selectors-4/#the-focus-pseudo
- https://www.w3.org/TR/WCAG21/#focus-visible
- http://webaim.org/techniques/keyboard/
- http://www.outlinenone.com/#test2