Nbd, but it sounds like you’re talking about encapsulation of event capture (viewport stops receiving events after losing focus).
CORS is a protocol for client-side enforcement of a server-side security policy. It ensures that a resource request (e.g. “my-totally-safe-resource.wasm”) only loads from a location your server permits (e.g. “my-valid-origin.biz”, “friends-valid-origin.org”, etc).