Go to original example.

Lessons learned:

• Original example adds a focus class to the checkbox but it is unused from what I could tell; so I have chosen to omit it.
• aria-controls feels like it makes it harder to get it right, since relying on the DOM to be able to find/derive state is more work than simply passing the state down through a framework. I decided to bypass this by using Svelte bind:this to give the Checkbox a reference to the rendered DOM node. This gives me access to the element's ID.