When building reusable web components with Lit, you often want to let users insert their own content inside your component. The <slot> element provides this flexibility by acting as a placeholder for external content. When a Lit component renders, any content placed between its opening and closing tags in HTML will be projected into the corresponding <slot> inside the component's template.

You can use a default slot—a plain <slot> with no name—to accept any content not assigned to a specific slot. This is useful for simple components where all external content should appear in the same place. For more complex scenarios, you can define named slots using the name attribute: <slot name="header"></slot>. Users can then assign content to a specific slot by setting the slot attribute on an element: <div slot="header">.

If no external content is provided for a slot, Lit will display any fallback content inside the <slot> tags. This allows you to define default messages or structure that appears unless the user supplies their own content.