Type Safety

How important is this part? What does it do? I'm fairly new to ts, googled but still cant wrap my head around

// Register the router instance for type safety
declare module '@tanstack/react-router' {
  interface Register {
    router: typeof router
  }
}

// Register the router instance for type safety
declare module '@tanstack/react-router' {
  interface Register {
    router: typeof router
  }
}

// Register the router instance for type safety
declare module '@tanstack/react-router' {
  interface Register {
    router: typeof router
  }
}

// Register the router instance for type safety
declare module '@tanstack/react-router' {
  interface Register {
    router: typeof router
  }
}