From 7e5e0a587e8584e44d1720173c6fdb9a3db520b9 Mon Sep 17 00:00:00 2001
From: Georg Lukas <georg@op-co.de>
Date: Wed, 22 Feb 2017 11:27:27 +0100
Subject: [PATCH] XEP-0280: clearly specify MUC-related rules

---
 xep-0280.xml | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/xep-0280.xml b/xep-0280.xml
index 3e7ea708..8d860694 100644
--- a/xep-0280.xml
+++ b/xep-0280.xml
@@ -284,6 +284,16 @@
       <li>it is of type "chat".</li>
       <li>it is of type "normal" and contains a &lt;body&gt; element.</li>
       <li>it is of type "error" and it was sent in response to a &MESSAGE; that was eligible for carbons delivery (Note that as this would require message tracking and correlation on the server, it is unlikely to be generally appropriate for most implementations).</li>
+      <li>it matches the MUC-related rules outlined below.</li>
+    </ul>
+    <p>To properly handle messages exchanged with a MUC (or similar service), the server must be able to identify MUC-related messages. This can be accomplished by tracking the clients' presence in MUCs, or by checking for the <tt>&lt;x xmlns="http://jabber.org/protocol/muc#user"&gt;</tt> element in messages. The following rules are suggested for MUC-related messages:
+    </p>
+    <ul>
+      <li>A &MESSAGE; of type "groupchat" SHOULD NOT be carbon-copied.</li>
+      <li>A &MESSAGE; containing a &xep0249; SHOULD be carbon-copied.</li>
+      <li>A &MESSAGE; containing a <link url='https://xmpp.org/extensions/xep-0045.html#invite-mediated'>Mediated Invitation</link> SHOULD be carbon-copied.</li>
+      <li>A private &MESSAGE; from a local user to a MUC participant (sent to a full JID) SHOULD be carbon-copied<note>The server SHOULD limit carbon-copying to the clients sharing a <strong>Multi-Session Nick</strong> in that MUC, and MAY inject the &lt;x/&gt; element into such carbon copies. Clients SHOULD ignore carbon-copies of MUC-PMs related to a MUC they are not joined to.</note>.</li>
+      <li>A private &MESSAGE; from a MUC participant (received from a full JID) to a local user SHOULD NOT be carbon-copied (these messages are already replicated by the MUC service to all joined client instances).</li>
     </ul>
     <p>As this is a implementation detail of servers, clients MUST NOT rely on the server implementing a particular set of rules for which messages are eligible for Carbons delivery.</p>
     <p>Future specifications may have more precise requirements on which messages need to be eligible for carbons delivery; such future specifications will provide their own discovery and negotiation mechanisms, such that a client negotiating Carbons using the protocol defined in this specification will cause the server to consider messages eligible for Carbons delivery based on the requirements described herein.</p>