def subject(roomJID, subject):
    """
        Change the subject of a MUC room.

        See: http://xmpp.org/extensions/xep-0045.html#subject-mod

        @param roomJID: The bare JID of the room.
        @type roomJID: L{JID<twisted.words.protocols.jabber.jid.JID>}

        @param subject: The subject you want to set.
        @type subject: C{unicode}
        """
