<remark>Accepted by vote of Council on 2022-07-27.</remark>
</revision>
<revision>
<version>0.0.1</version>
<date>2022-07-11</date>
<initials>jp</initials>
<remark><p>First draft.</p></remark>
</revision>
</header>
<section1topic='Introduction'anchor='intro'>
<p>It is nowadays common to attach informations to messages or other items in various social networks: famous example are "like" (or "favourite") and "reactions" features.</p>
<p>While there are ways to attach informations to &MESSAGE; stanzas with extensions such as &xep0422; or &xep0444;, this is not the case for pubsub items</p>
<p>Some software use comments as a work-around for &xep0277;, by posting a single "♥" character to notify a "like". This has the advantage to work out of the box even if no specific implementation is done to manage this, but this has a couple of disadvantages:</p>
<ul>
<li>it only works with &xep0277;, it is not possible to like other kind of items;</li>
<li>it's polluting comments with an information which should be separated;</li>
<li>it doesn't handle uniqueness: a "like" should be doable only once per entity, but by using comments one can like thousand of times, and it's the receiving client which must ignore duplicates;</li>
<li>it doesn't scale: if thousand of people like a blog post, all comments must be retrieved and counted;</li>
<li>it's mixing metadata and content intended for human user;</li>
<li>this behaviour is found in the wild, but not standardized anywhere;</li>
</ul>
<p>This XEP proposes an alternative and generic solution, which can work with any kind of pubsub item.</p>
</section1>
<section1topic='Requirements'anchor='reqs'>
<p>The design goal of this XEP are:</p>
<ul>
<li>work with any kind of pubsub item, not only &xep0277;</li>
<li>handle uniqueness of attachment per JID</li>
<li>have an extensible mechanism for future use</li>
<li>re-use pubsub subscription and access control mechanism</li>
<li>optionally have a way to "group" or "summarize" informations: get a summary of all attachment without needing to retrieve each of them individually.</li>
</ul>
<p>To facilitate the bootstrapping of this XEP, it is also designed to work in a basic way with generic pubsub service. However, some implementation work is necessary to offer the full potential of the XEP (and notably to be able to scale).</p>
</section1>
<section1topic='Glossary'anchor='glossary'>
<ul>
<li><strong>like/favourite</strong>: a common way to indicate interest in item</li>
<li><strong>attachment node</strong>: node where attached data of an item are published</li>
<li><strong>summary node</strong>: node managed by pubsub service which keep a summary of all attachment of target items</li>
<li><strong>target item</strong>: item to which metadata is attached</li>
<li><strong>target node</strong>: pubsub node where target items are published</li>
<li><strong>attachment item</strong>: item of the attachment node containing attachments by a specific JID</li>
<li><strong>summary item</strong>: item of the summary node linked to a target item</li>
<li><strong>attachment</strong>: child element of the <attachments> element, describing a metadata attached to a target item</li>
</ul>
</section1>
<section1topic='Use Cases'anchor='usecases'>
<section2topic="Basic Usage"anchor="basic">
<p>Romeo wants to indicate to Juliet that he has noticed her post about the balcony restoration. This &xep0277; item has been published on the PEP service of Juliet at service juliet@capulet.lit on the node 'urn:xmpp:microblog:0' and the item has the ID 'balcony-restoration-afd1'.</p>
<p>Few seconds later, Romeo reacts with some emojis, it does that with the following item, and his client takes care of keeping the <noticed> element above:</p>
<examplecaption="Romeo Add Reactions To Juliet Publication"><