declare nref on NIP-33. remove need for NIP-01 bridge event.

33.md

@@ -12,10 +12,10 @@ Implementation
 --------------
 The value of a tag is defined as the first parameter of a tag after the tag name.
 
-A *parameterized replaceable event* is defined as an event with a kind `30000 <= n < 40000`.  
+A *parameterized replaceable event* is defined as an event with a kind `30000 <= n < 40000`.
 Upon a parameterized replaceable event with a newer timestamp than the currently known latest
 replaceable event with the same kind and first `d` tag value being received, the old event
-SHOULD be discarded and replaced with the newer event.  
+SHOULD be discarded and replaced with the newer event.
 A missing or a `d` tag with no value should be interpreted equivalent to a `d` tag with the
 value as an empty string. Events from the same author with any of the following `tags`
 replace each other:
@@ -30,6 +30,20 @@ replace each other:
 
 Clients SHOULD NOT use `d` tags with multiple values and SHOULD include the `d` tag even if it has no value to allow querying using the `#d` filter.
 
+Referencing and tagging
+-----------------------
+
+Normally (as per NIP-01, NIP-12) the `"p"` tag is used for referencing public keys and the
+`"e"` tag for referencing event ids and the `note`, `npub`, `nprofile` or `nevent` are their
+equivalents for event tags (i.e. an `nprofile` is generally translated into a tag
+`["p", "<event hex id>", "<relay url>"]`).
+
+To support linking to parameterized replaceable events, the `nref` code is introduced on
+NIP-19. It includes the public key of the event author and the `d` tag (and relays) such that
+the referenced combination of public key and `d` tag can be found.
+
+The equivalent in `tags` to the `nref` code is the tag `"f"`, comprised of `["f", "<pubkey>:<d-identifier>", "<relay url>"]`.
+
 Client Behavior
 ---------------