Next.js Parallel Routes Allow Multiple Pages to Render Within One Layout

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Next.js App Router supports a feature called Parallel Routes, which enables multiple pages to render simultaneously within a single layout without replacing one another. Developers define independent rendering areas using named slots — special folders prefixed with '@' — each of which receives its own navigation state and props in the layout component. Unlike nested layouts, changes in one parallel slot do not affect the others, making it ideal for dashboards, sidebars, and modal overlays. A 'default.tsx' file must be provided for each slot to handle cases where no matching route exists, preventing 404 errors. A common use case is opening a detail modal over a content page while preserving the underlying view and sharing a unique URL.

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