Specify the use of a delay element in the initial subject message.
After the room has optionally sent the discussion history to the new occupant, it SHALL send the current room subject. This is a &MESSAGE; stanza from the room JID (or from the occupant JID of the entity that set the subject), with a &SUBJECT; element but no &BODY; element, as shown in the following example.
+After the room has optionally sent the discussion history to the new occupant, it SHALL send the current room subject. This is a &MESSAGE; stanza from the room JID (or from the occupant JID of the entity that set the subject), with a &SUBJECT; element but no &BODY; element, as shown in the following example. In addition, the subject SHOULD be stamped with &xep0203; information qualified by the 'urn:xmpp:delay' namespace to indicate the time at which the subject was last modified. If the <delay/> element is included, its 'from' attribute MUST be set to the JID of the room itself.
If there is no subject set, the room MUST return an empty &SUBJECT; element.
+Interoperability Note: The <delay/> element has been specified in version 1.34.0 of this document. Hence, consuming entities need to be able to deal with servers which do not send a <delay/> element. Most notably, this means that the presence of the <delay/> element cannot be used to distinguish a historic vs. a live subject change.
+If there is no subject set, the room MUST return an empty &SUBJECT; element. The <delay/> SHOULD be included if the subject was actively cleared and MAY be omitted if the room never had a subject set.