xep-0461.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE xep SYSTEM 'xep.dtd' [
        <!ENTITY % ents SYSTEM 'xep.ent'>
        %ents;
        ]>
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
<xep>
  <header>
    <title>Message Replies</title>
    <abstract>
      This document defines a way to indicate that a message is a reply to a previous message.
    </abstract>
    &LEGALNOTICE;
    <number>0461</number>
    <status>Experimental</status>
    <type>Standards Track</type>
    <sig>Standards</sig>
    <approver>Council</approver>
    <dependencies/>
    <supersedes/>
    <supersededby/>
    <shortname>reply</shortname>
    <author>
      <firstname>Natalie</firstname>
      <surname>Wirth</surname>
      <email>nataliew@laposte.net</email>
    </author>
    <author>
      <firstname>Marvin</firstname>
      <surname>Wissfeld</surname>
      <email>xsf@larma.de</email>
      <jid>jabber@larma.de</jid>
    </author>
    <revision>
      <version>0.2.0</version>
      <date>2022-12-09</date>
      <initials>nc</initials>
      <remark>Fix example character counting. Add disco feature. Relax the 'to' attribute constraints.</remark>
    </revision>
  <revision>
    <version>0.1.0</version>
    <date>2022-01-25</date>
    <initials>XEP Editor (jsc)</initials>
    <remark>Accepted by vote of Council on 2022-01-05.</remark>
  </revision>
    <revision>
      <version>0.0.1</version>
      <date>2022-01-01</date>
      <initials>nw/mw</initials>
      <remark>
        <p>First draft.</p>
      </remark>
    </revision>
  </header>

  <section1 topic='Introduction' anchor='intro'>
    <p>
      When commenting on a previous message, it is sometimes desired to clarify which message the comment refers to.
      Currently, &xep0393; quotes are commonly used for that purpose. However, this format does not allow receiving
      clients to properly identify the referenced message or to adjust the user interface accordingly.
    </p>
    <p>
      This specification defines a way to indicate that a message is a reply to a previous message. It does not intend
      to provide means to create sub-threads for a message.
    </p>
  </section1>

  <section1 topic='Discovering support' anchor='disco'>
    <p>
      If a client implements message replies, it MUST specify the 
      'urn:xmpp:reply:0' feature in its service discovery information features
      as specified in &xep0030; and the Entity Capabilities profile specified in &xep0115;.
    </p>
    <example caption='Client requests information about a chat partner&apos;s client'><![CDATA[
  <iq type='get'
      to='romeo@montague.lit/orchard'
      from='juliet@capulet.lit/balcony'
      id='info1'>
    <query xmlns='http://jabber.org/protocol/disco#info'/>
  </iq>]]></example>
    <example caption='Partner&apos;s client advertises support for replies'><![CDATA[
  <iq type='result'
      to='juliet@capulet.lit/balcony'
      from='romeo@montague.lit/orchard'
      id='info1'>
    <query xmlns='http://jabber.org/protocol/disco#info'>
  ...
      <feature var='urn:xmpp:reply:0'/>
  ...
    </query>
  </iq>]]></example>
  </section1>

  <section1 topic='Use Cases' anchor='usecases'>
    <p>
      To indicate that a message is a reply, a &lt;reply&gt; element in the urn:xmpp:reply:0 namespace is placed in the
      message stanza. The &lt;reply&gt; element SHOULD have a 'to' attribute containing the full jid of the author of the
      referenced message and MUST have an 'id' attribute containing the id of the referenced message.
      In a 1:1 chat context, a bare jid MAY be used instead of a full jid.
    </p>
    <example caption="Max replies to Anna's message"><![CDATA[
<message to='max@example.com' from='anna@example.com/tablet' id='message-id1' type='chat'>
  <body>We should bake a cake</body>
</message>

<message to='anna@example.com' id='message-id2' type='chat'>
  <body>Great idea!</body>
  <reply to='anna@example.com/tablet' id='message-id1' xmlns='urn:xmpp:reply:0' />
</message>]]></example>

    <section2 topic='Compatibility Fallback' anchor='compat'>
      <p>
        To provide a fallback for non-supporting clients, the sending client MAY include fallback text in the body and
        indicate it via Compatibility Fallback.
        Note that the following example is formatted for readability and that the indentation, leading and trailing new lines
        of the example body element should not be taken into account.
      </p>
      <example caption="Anna replies to a message and includes a fallback"><![CDATA[
<message to='anna@example.com' id='message-id3' type='chat'>
  <body>
    > Anna wrote:
    > We should bake a cake
    Great idea!
  </body>
  <reply to='anna@example.com/laptop' id='message-id1' xmlns='urn:xmpp:reply:0' />
  <fallback xmlns='urn:xmpp:feature-fallback:0' for='urn:xmpp:reply:0'>
    <body start="0" end="38" />
  </fallback>
</message>]]></example>

      <p>
        The receiving client SHOULD NOT display the compatibility fallback if it renders the referenced message
        alongside the reply in some way. However, if the receiving client does not display the referenced message, for
        example because it doesn't know the referenced id, it MAY display the compatibility fallback instead.
      </p>
    </section2>
  </section1>

  <section1 topic='Business Rules' anchor='rules'>
    <p>Answers MUST NOT be be assumed to relate to any other messages than the referenced one.</p>
    <section2 topic='Using the correct ID' anchor='business-id'>
      <p>
        For messages of type 'groupchat', the stanza's 'id' attribute MUST NOT be used for replies. Instead, in group
        chat situations, the ID assigned to the stanza by the group chat itself must be used. This is discovered in a
        &lt;stanza-id&gt; element with a 'by' attribute that matches the bare JID of the group chat, as defined
        in &xep0359;.
      </p>
      <p>
        This implies that group chat messages without a &xep0359; stanza-id cannot be replied to.
      </p>
      <p>
        For other message types the sender should use the 'id' from a &xep0359;
        &lt;origin-id&gt; if present, or the value of the 'id' attribute on the
        &lt;message&gt; otherwise.
      </p>
    </section2>
  </section1>

  <section1 topic='IANA Considerations' anchor='iana'>
    <p>This document requires no interaction with &IANA;.</p>
  </section1>

  <section1 topic='XMPP Registrar Considerations' anchor='registrar'>
    <p>This document requires no interaction with &REGISTRAR;.</p>
  </section1>

</xep>