What does <Fragment> (or <>...</>) solve, and when must you use the long form <Fragment key={...}> instead of the shorthand?

Render a <Modal> into a DOM node outside the parent (e.g., document.getElementById('modal-root')). Explain the portal event bubbling quirk: where does a click inside the modal propagate to?

What changes when you wrap an app in <StrictMode> in a React 18 dev build? Pick the three concrete behaviors and explain why each one exists.