TODO

Event.focusIn && Event.focusOut
  JSX onFocusIn ?
  addEventListener('focusIn') ?

HTMLPictureElement
  Is it possible (and a good idea) to detect interaction with
  HTMLPictureElement instances? Maybe look for JSX `<picture>` and for
  document.createElement('picture')?

Intl.~locale.xxx
  It would be possible to match on literal string arguments to Intl functions
  to be able to detect _some_ locale references - but most references would
  likely be opaque in real-world use cases. Matching specific local chunks
  is probably best kept out of this library's scope.

ResizeObserver
  see https://github.com/Microsoft/TypeScript/issues/28502