diff --git a/01.md b/01.md
index e4c0546c..1831438e 100644
--- a/01.md
+++ b/01.md
@@ -66,7 +66,9 @@ This NIP defines 3 standard tags that can be used across all event kinds with th
 
 - The `e` tag, used to refer to an event: `["e", <32-bytes lowercase hex of the id of another event>, <recommended relay URL, optional>]`
 - The `p` tag, used to refer to another user: `["p", <32-bytes lowercase hex of a pubkey>, <recommended relay URL, optional>]`
-- The `a` tag, used to refer to a parameterized replaceable event: `["a", <kind integer>:<32-bytes lowercase hex of a pubkey>:<d tag value>, <recommended relay URL, optional>]`
+- The `a` tag, used to refer to a (maybe parameterized) replaceable event
+    - for a parameterized replaceable event: `["a", <kind integer>:<32-bytes lowercase hex of a pubkey>:<d tag value>, <recommended relay URL, optional>]`
+    - for a non-parameterized replaceable event: `["a", <kind integer>:<32-bytes lowercase hex of a pubkey>:, <recommended relay URL, optional>]`
 
 As a convention, all single-letter (only english alphabet letters: a-z, A-Z) key tags are expected to be indexed by relays, such that it is possible, for example, to query or subscribe to events that reference the event `"5c83da77af1dec6d7289834998ad7aafbd9e2191396d75ec3cc27f5a77226f36"` by using the `{"#e": "5c83da77af1dec6d7289834998ad7aafbd9e2191396d75ec3cc27f5a77226f36"}` filter.