diff --git a/172.md b/172.md
index 84a88c92..d2b7a533 100644
--- a/172.md
+++ b/172.md
@@ -79,6 +79,10 @@ The post-approval event MUST include `a` tags of the communities the moderator i
 
 It's recommended that multiple moderators approve posts to avoid deleting them from the community when a moderator is removed from the owner's list. In case the full list of moderators must be rotated, the new moderator set must sign new approvals for posts in the past or the community will restart. The owner can also periodically copy and re-sign of each moderator's approval events to make sure posts don't dissapear with moderators. 
 
+Replaceable events can be submitted for approval in two ways: (i) by their `e` tag if moderators want to approve each individual change to the repleceable event or (ii) by the `a` tag if the moderator trusts the original post author to not modify the event beyond community rules. 
+
+Clients SHOULD evaluate any non-`34550:*` `a` tag as posts to be included in all `34550:*` `a` tags.  
+
 # Displaying
 
 Community clients SHOULD display posts that have been approved by at least 1 moderator or by the community owner.