A *replaceable event* is defined as an event with a `replaceable` tag with value `1`. Relays SHOULD treat unknown types as if the event is not replaceable.
Upon a replaceable event with a newer timestamp than the currently known latest replaceable event with the same kind, the old event SHOULD be discarded and replaced with the newer event.
An *ephemeral event* is defined as an event with an `ephemeral` tag with value `1`. Relays are RECOMMENDED to reject unknown types for future extensions.
Clients SHOULD use the `supported_nips` field to learn if a relay supports generic tag queries. Clients SHOULD NOT send ephemeral events to relays that do not support this NIP; they will be persisted. Clients MAY send replaceable events to relays that may not support this NIP, and clients querying SHOULD be prepared for the relay to send multiple events and should use the latest one.