Sometimes you may want to split a large component, but it doesn't make sense to use a top-level component because it requires context of the parent, for example an <Accordion />. To create a sub component, you can place a directory inside the parent.

components/
    Accordion/
        Item/
            template.twig

To use a sub component, include a . in the component name:

<Accordion>
    <Accordion.Item>...</Accordion.Item>
</Accordion>