Update 40.md

40.md

@@ -6,8 +6,7 @@ Expiration Timestamp
 
 `draft` `optional` `author:0xtlt`
 
-The `expiration` tag enables users to specify a timestamp at UTC-0 at which the message should be considered expired and deleted by relays (or just ignored by clients). This can be useful for making temporary announcements, making limited-time offers, or sending ephemeral messages but should not be seen as a security solution for the content of your messages.
-So be careful when sharing confidential information.
+The `expiration` tag enables users to specify a unix timestamp at which the message SHOULD be considered expired (by relays and clients) and SHOULD be deleted by relays.
 
 #### Spec
 
@@ -39,7 +38,7 @@ Client Behavior
 
 Clients SHOULD use the `supported_nips` field to learn if a relay supports this NIP. Clients SHOULD NOT send expiration events to relays that do not support this NIP.
 
-Clients MUST ignore events that have expired.
+Clients SHOULD ignore events that have expired.
 
 Relay Behavior
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