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<xep>
<header>
  <title>Message Attaching</title>
  <abstract>
    This specification defines a method for indicating that a message contains
    content which describes an earlier message in the conversation and should
    be grouped with the earlier message.
  </abstract>
  &LEGALNOTICE;
  <number>0367</number>
  <status>Deferred</status>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <approver>Council</approver>
  <dependencies>
    <spec>XMPP Core</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>message-attaching</shortname>
  &sam;
  <author>
    <firstname>Craig</firstname>
    <surname>Petchell</surname>
    <email>cpetchell@atlassian.com</email>
  </author>
  <revision>
    <version>0.2</version>
    <date>2017-09-11</date>
    <initials>XEP Editor (jwi)</initials>
    <remark>Defer due to lack of activity.</remark>
  </revision>
  <revision>
    <version>0.1</version>
    <date>2015-12-15</date>
    <initials>XEP Editor (asw)</initials>
    <remark><p>Initial published version approved by the XMPP Council.</p></remark>
  </revision>
  <revision>
    <version>0.0.1</version>
    <date>2015-10-16</date>
    <initials>ssw</initials>
    <remark><p>First draft.</p></remark>
  </revision>
</header>
<section1 topic='Introduction' anchor='intro'>
  <p>
    Many messaging applications send special messages which include more
    information about a previous message. For example, when sending a link the
    service may display the description or an image off the page, or users may
    respond to a message with a "sticker" or an "emotion" which they wish to
    display alongside the message, even though the conversation has moved on.
  </p>
  <p>
    This specification defines a way by which one can indicate that a message
    is logically (and visibly) "attached" to an earlier message in the
    conversation.
  </p>
</section1>
<section1 topic='Discovering support' anchor='disco'>
  <p>
    If a client implements message attaching, it MUST specify the
    'urn:xmpp:message-attaching: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'
    from='alonso@naples.lit/ship'
    id='miuARo9V'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>]]></example>
  <example caption='Partner&apos;s client advertises support for attaching'><![CDATA[
<iq type='result'
    to='alonso@naples.lit/ship'
    from='naples.lit'
    id='miuARo9V'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
…
    <feature var='urn:xmpp:message-attaching:0'/>
…
  </query>
</iq>]]></example>
</section1>
<section1 topic='Usage' anchor='usage'>
  <p>
    Messages that are attached to other messages MUST contain an
    &lt;attach-to/&gt; element qualified by the 'urn:xmpp:message-attaching:0'
    namespace and with an 'id' attribute set to the ID of the message that we
    want to attach to. Messages MAY be attached to any other message, including
    those sent by other clients, but clients MAY choose to ignore the attach-to
    directive and display the message normally.
  </p>
  <example caption='User attaches a message'><![CDATA[
<message to='antonio@milan.lit/ship' from='prospero@milan.lit/island id='RgEGnjqy'>
  <body>storm.png</body>
  <attach-to id='oldmessage1' xmlns='urn:xmpp:message-attaching:0'/>
</message>]]></example>
  <p>
    Note that indicating that a message should be "attached" to an earlier
    message in the conversation is merely a suggestion to the client to display
    the message next to or below the old message.
  </p>
</section1>
<section1 topic='Business Rules' anchor='rules'>
  <p>
    A receiving client MAY choose to show the attached message next to or below
    the indicated message in whatever display is used for messages or can
    choose to display the attachment in another way (including as a normal
    message, completely ignoring the attach-to element).
  </p>
  <p>
    A receiving client SHOULD indicate that the message is an attachment, and
    not a part of the original message to prevent confusion.
  </p>
  <p>
    &lt;attach-to/&gt; elements MUST NOT be put on any stanza type other than
    messages.
  </p>
  <p>
    A server may choose to strip some &lt;attach-to/&gt; messages based on
    local policy (eg. a server might have a policy that only it can create
    message attachments).
  </p>
  <p>Clients MUST send ids on messages if they support attachments.</p>
  <p>
    Messages MUST NOT contain more than one &lt;attach-to/&gt; element.
  </p>
  <p>
    Clients and servers MUST NOT include an &lt;attach-to/&gt; element on
    messages with a non-messaging payload unless they are including it on an
    error which may be attached to the message that caused the error to be
    generated.
  </p>
</section1>
<section1 topic='Security Considerations' anchor='security'>
  <p>
    Clients that implement message attachments MUST be careful not to display
    the attachments in such a way that they could be confused with the original
    message and cause someone viewing the conversation to assume they were sent
    by the sender of the message being attached to.
  </p>
</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 specification defines the following XML namespaces:</p>
	<ul>
		<li>urn:xmpp:message-attaching:0</li>
	</ul>
	<p>
    The &REGISTRAR; shall include the foregoing namespaces in its disco
    features registry as defined in &xep0030;.
	</p>
	<code caption='Registry Submission'><![CDATA[
<var>
	<name>urn:xmpp:message-attaching:0</name>
	<desc>Indicates support for attaching one message to another.</desc>
	<doc>XEP-xxxx</doc>
</var>
]]></code>
</section1>
<section1 topic='XML Schema' anchor='schema'>
  <code><![CDATA[
<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:message-attaching:0'
    xmlns='urn:xmpp:message-attaching:0'
    elementFormDefault='qualified'>

  <xs:element name='attach-to'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='xs:string'>
          <xs:attribute name='id' type='xs:string' use='required'/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

</xs:schema>
]]></code>
</section1>
</xep>
