Cookie access control is based on domain, (optionally) path and (optionally) URL scheme (
The behaviour of HTTP cookies in real life browsers is not described in any RFC (thus quoting a RFC to describe cookies is almost always wrong). The various RFC are of historical interest.
Browsers are recommended to allow at least 20 cookies per domain and 4KB per cookie. If you are looking for an alternative to cookies that aren't sent in HTTP headers and can store more data, consider