Sometimes browsers add features when you're not looking. See `<details>`. mozilla 
<details> <summary>Knock knock.</summary> <p>Who's there?</p> </details>
Who's there?
Knock knock.
.
As of this writing, it's not yet supported by Internet Explorer.
https://caniuse.com/#search=details HEIGHT 600
.
Eric demoed the code behind and how during the weekly Wiki Dev/User Video Chat Nov 28 meeting with Ward. Leading to a wide discussion about capabilities and widget safety.