^This. Closing an entire application with the possibility of losing important state? No, we don't want a button that does that (though a button combination is O

^This. Closing an entire application with the possibility of losing important state? No, we don't want a button that does that (though a button combination is OK because that's less likely to be accidentally triggered). Closing an ephemeral popup that is distracting from the main page? Absolutely, `Esc` that.