<abstract>This specification allows multiple clients of the same user to synchronize the displayed state of their chats.</abstract>
&LEGALNOTICE;
<number>xxxx</number>
<status>ProtoXEP</status>
<type>Standards Track</type>
<sig>Standards</sig>
<approver>Council</approver>
<dependencies>
<spec>XMPP Core</spec>
<spec>XEP-0001</spec>
<spec>Etc.</spec>
</dependencies>
<supersedes/>
<supersededby/>
<shortname>mds</shortname>
<author>
<firstname>Daniel</firstname>
<surname>Gultsch</surname>
<email>daniel@gultsch.de</email>
<jid>daniel@gultsch.de</jid>
</author>
<revision>
<version>0.0.1</version>
<date>2024-02-21</date>
<initials>dg</initials>
<remark><p>First draft.</p></remark>
</revision>
</header>
<section1topic='Introduction'anchor='intro'>
<p>In multi-device environments marking a chat as <em>displayed</em> on one device should mark that chat as <em>displayed</em> on all devices. Historically carbon copies (&xep0280;) of the <displayed/> element of Chat Markers (&xep0333;) have been used to achieve this effect. However this approach has a couple of downsides that this specification is trying eliminate:</p>
<ul>
<li>The contact has to request Chat Markers by tagging a message with <markable/>.</li>
<li>Chat Markers let the contact know that a device has displayed the message. This might not always be advisable when synchronization across multiple devices of the same user is the desired outcome.</li>
<li>When used in large group chats Chat Markers can create a lot of unwanted traffic.</li>
</ul>
<p>This specification isolates the task of multi-device synchronization from providing information to the contact, while borrowing some of the semantics of Chat Markers such as <em>displayed</em> refering to all messages up to this point.</p>
</section1>
<section1topic='Requirements'anchor='reqs'>
<ul>
<li>Basic functionality should not depend on server features that go beyond what is commonly implemented at the time of writing this specification.</li>
<li>Rely on server-injected <stanza-id/> (see &xep0359;) to provide unique and stable IDs. While this is commonly done as part of &xep0313; it does not technically depend on the message being archived.</li>
<li>Define the interaction with &xep0333;.</li>
<li>Provide optional methods for traffic optimizations on supporting servers.</li>
<li>Make no assertions on what constitutes an <em>open</em> or <em>archived</em> chat. This specification allows clients to state that they have displayed messages in a certain chat up to a certain point. It does not indicate that a chat is open or in case of group chats joined.</li>
</ul>
</section1>
<section1topic='Glossary'anchor='glossary'>
<dl>
<di>
<dt>Displayed</dt>
<dd>
Colloquially this is also known as <em>read</em>. However since a common implementation of <em>read</em> is: "shown on screen, in full, in the context of the chat", and this gives no indication on whether the user has actually read a message, <em>displayed</em> was chosen as a more accurate terminology. A message might also be manually acknowledged by the user, for example via a <em>mark as read</em> action in a notification. Implementations are also possible, for example in smart home devices or infotainment systems, where the message is read aloud by a Text-to-Speech system, but never actually displayed. It is up to the implementors discretion to determine what the best approximation of <em>the user has had a reasonable chance to mentally process the message</em> is.
<p>Clients use items in a private PEP (&xep0163;) node called 'urn:xmpp:mds:displayed:0' to synchronize and persist the displayed state (See &xep0223;). The item ID corresponds to the JID of the respective chat. For normal, 1:1 chats this SHOULD be the bare JID of the contact, for group chats this SHOULD be the bare JID of the room and for private messages in group chats the full JID of the participant.</p>
<p>The item contains a single <displayed/> element qualified by the 'xrn:xmpp:mds:displayed:0' namespace. The <displayed/> element MUST contain exactly one &xep0359;<stanza-id/> element that corresponds to the stanza-id of the most recent, displayed message, in that particular chat.</p>
<section2topic="Flagging chat as displayed"anchor='publish'>
<p>Only messages <strong>received</strong> by the user (meaning sent by third parties such as a contact, a participant in a group chat, etc) SHOULD be flagged as 'displayed'. However since 'displayed' means <em>all messages up to this point</em> and the stanza-id of a message <strong>sent</strong> by the user indicates a valid point in the chat history, sent messages MAY be flagged as well.</p>
<p>Flagging a chat as <em>displayed up to this point</em> happens by publishing a PEP item with an id corresponding to the JID of the chat and a <displayed/> payload element into the 'urn:xmpp:mds:displayed:0' node.</p>
<p>For group chats the <stanza-id/> child of the <displayed/> element refers to the stanza-id injected by the room. For all other chats the stanza-id child refers to the stanza-id injected by the user’s server (the server hosting the user account).</p>
<p>The client MUST include appropriate publish-options in the publication, including, but not limited to, setting the access model to whitelist and the max-items to max.</p>
<examplecaption='Client marks a chat as display'><