1. Explain the revalidate option in getStaticProps and how ISR works behind the scenes.
The revalidate option in getStaticProps specifies the number of seconds after which Next.js should attempt to regenerate the page in the background, implementing ISR by serving stale content instantly while regenerating fresh content asynchronously. When a request comes after the revalidate period, the user still sees the cached version immediately for fast response, Next.js triggers a background regeneration on the server, and once complete, the cache updates so subsequent requests see the new version. If regeneration fails, the old cached version continues serving to ensure availability, and you can set revalidate to false or omit it for pure SSG with no regeneration, or use on-demand revalidation with revalidatePath or revalidateTag for more control. This approach provides static-like performance with near-real-time content updates without constant server rendering costs.