When issues on the `on-demand-isr` repo change (get created, commented on, deleted, etc), GitHub fires off a webhook and the impacted pages get re-rendered and pushed to the edge, on demand. The webhook on the Next.js app side executes a new `revalidatePath()` API call.

Unlike `revalidate` with a time interval, a Serverless Function is invoked _only when content changes_, making it faster for the user (they see changes immediately), and more cost-efficient for owners.