UI engineers and A11y SMEs need to tracks focus assiduously. `document.activeElement` is not enough; it cannot descend into an iframe or shadowDOM.

focus-live-expressions

# Chrome devtools 'live expressions' for `focus`

## Regular DOM

```
document.activeElement
```

## Inside a StoryBook iframe DOM
	
```
document.getElementById("storybook-preview-iframe").contentWindow.document.activeElement
```

## Inside ShadowDOM

```
(function getDeepActiveElement(root){
  const activeEl = root.activeElement;
  if (!activeEl) return null;
  if (activeEl.shadowRoot) return getDeepActiveElement(activeEl.shadowRoot);
  return activeEl;
})(document)
```