Nested composition

A component within a component within a component. Each <tick-counter> lives inside a <counter-row>, which lives inside a <counter-board> — three levels, all light DOM.

1. Click a few counters so their counts differ.
2. Click Rename board. That changes only the board's title and re-renders the root component.
3. The counts stay exactly as you left them. A nested component owns the DOM it renders for itself; an ancestor re-render patches props down but never trims the inner subtree.