Introduce <x/> tag in MUC-PMs to support better Carbon delivery.
+Since each occupant has its own occupant JID, an occupant can send a "private message" to a selected occupant via the service by sending a message to the intended recipient's occupant JID. The message type SHOULD be "chat" and MUST NOT be "groupchat", but MAY be left unspecified (i.e., a normal message). This privilege is controlled by the "muc#roomconfig_allowpm" room configuration option.
+To allow for proper synchronization of these messages to the user's other clients by &xep0280;, the sending client SHOULD add an <x/> element qualified by the 'http://jabber.org/protocol/muc#user' namespace to the message.
+Note: because this requirement was only added in revision 1.28 of this XEP, receiving entities MUST NOT rely on the existence of the <x/> element on private messages for proper processing.
The service is responsible for changing the 'from' address to the sender's occupant JID and delivering the message to the intended recipient's full JID.
+The service is responsible for changing the 'from' address to the sender's occupant JID and delivering the message to the intended recipient's full JID. The service SHOULD add the <x/> element if the message does not contain it already.
If the sender attempts to send a private message of type "groupchat" to a particular occupant, the service MUST refuse to deliver the message (since the recipient's client would expect in-room messages to be of type "groupchat") and return a &badrequest; error to the sender: