help: Update documentation for new deletion feature.

docs/production/security-model.md

@@ -129,8 +129,9 @@ strength allowed is controlled by two settings in
 
   - Message content can only ever be modified by the original author.
 
-  - Any message visible to an organization owner or administrator can
-    be deleted at any time by that administrator.
+  - Organization administrators can configure who has permission to
+    delete their own message, and who can delete other users'
+    messages that they can see.
 
   - See
     [Restrict message editing and deletion](https://zulip.com/help/restrict-message-editing-and-deletion)

help/delete-a-message.md

@@ -5,9 +5,9 @@ if these actions are allowed in your organization. Only server administrators
 can restore deleted messages.
 
 Organization administrators can
-[configure](/help/restrict-message-editing-and-deletion) who can edit and delete
-messages, and set time limits for these actions. Administrators can delete other
-users' messages completely, but cannot edit a message to delete its content.
+[configure](/help/restrict-message-editing-and-deletion) who can edit
+and delete their who messages, set a time limits for such deletions,
+and configure who can delete any message.
 
 ## Delete message content
 

help/moderating-open-organizations.md

@@ -39,7 +39,7 @@ problematic behavior.
   [edit](/help/restrict-message-editing-and-deletion#configure-message-editing-permissions)
   and
   [delete](/help/restrict-message-editing-and-deletion#configure-message-deletion-permissions)
-  their own messages, and set time limits on message editing and deletion.
+  messages, and set time limits on message editing and deletion.
 * If you are concerned about impersonation, you can [prevent users from changing
   their name](/help/restrict-name-and-email-changes#restrict-name-changes), or
   [require unique

help/restrict-message-editing-and-deletion.md

@@ -36,17 +36,15 @@ irretrievably) removes the message from Zulip.
 
 ## Configure message deletion permissions
 
-!!! tip ""
-
-    Administrators can always delete any message.
-
 {start_tabs}
 
 {settings_tab|organization-permissions}
 
 1. Under **Message deletion**:
+    - Configure **Who can delete any message**.
     - Configure **Who can delete their own messages**.
-    - Configure **Time limit for deleting messages**.
+    - Configure **Time limit for deleting messages**, which restricts
+      your own messages.
 
 {!save-changes.md!}