HTML tags in summary

Here we analyze, which types of HTML tags are allowed inside the summary field.

As the content field, the [summary field(https://www.w3.org/TR/activitystreams-vocabulary/#dfn-summary) is described as

A natural language summarization of the object encoded as HTML.

This is a somewhat petulant table as most Fediverse applications treat the summary field as a plain text content warning.

Sanitizing fields is desired behavior as seen in Section B.10 of ActivityPub.

Details

akkomagotosocialhollomastodonmisskeymitrapleromasharkey

summary	content	spoiler_text	Example
<b>bold</b>	<b>bold</b>	See summary
<strong>strong</strong>	<strong>strong</strong>	See summary
<i>italic</i>	<i>italic</i>	See summary
<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	See summary
<em>emphasis</em>	<em>emphasis</em>	See summary
<del>old</del><ins>new</ins>	<del>old</del><ins>new</ins>	See summary
<s>stricken</s>	<s>stricken</s>	See summary
<mark>mark</mark>	<mark>mark</mark>	See summary
find <var>x</var> (a variable)	find <var>x</var> (a variable)	See summary
<ol><li>ordered</li></ol>	<ol><li>ordered</li></ol>	See summary
<ul><li>unordered</li></ul>	<ul><li>unordered</li></ul>	See summary
<h1>h1</h1>	<h1>h1</h1>	See summary
<h2>h2</h2>	<h2>h2</h2>	See summary
<h3>h3</h3>	<h3>h3</h3>	See summary
<h4>h4</h4>	<h4>h4</h4>	See summary
<h5>h5</h5>	<h5>h5</h5>	See summary
<h1>h1</h1><h2>h2</h2>	<h1>h1</h1><h2>h2</h2>	See summary
<code>code</code>	<code>code</code>	See summary
<pre>pre</pre>	<pre>pre</pre>	See summary
line<br/>break	line<br/>break	See summary
<p>paragraph</p>	<p>paragraph</p>	See summary
<small>small</small>	<small>small</small>	See summary
<sup>sup</sup>	<sup>sup</sup>	See summary
<sub>sub</sub>	<sub>sub</sub>	See summary
<a href='https://funfedi.dev'>funfedi</a>	<a href='https://funfedi.dev'>funfedi</a>	See summary
<script>alert('hi');</script>	<script>alert('hi');</script>	See summary
<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />	<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />	See summary
wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	See summary
Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	See summary
Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	See summary

summary	content	spoiler_text	Example
<b>bold</b>	❌
<strong>strong</strong>	❌
<i>italic</i>	❌
<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	❌
<em>emphasis</em>	❌
<del>old</del><ins>new</ins>	❌
<s>stricken</s>	<s>stricken</s>	See summary
<mark>mark</mark>	<mark>mark</mark>	See summary
find <var>x</var> (a variable)	find <var>x</var> (a variable)	See summary
<ol><li>ordered</li></ol>	<ol><li>ordered</li></ol>	See summary
<ul><li>unordered</li></ul>	<ul><li>unordered</li></ul>	See summary
<h1>h1</h1>	<h1>h1</h1>	See summary
<h2>h2</h2>	<h2>h2</h2>	See summary
<h3>h3</h3>	<h3>h3</h3>	See summary
<h4>h4</h4>	<h4>h4</h4>	See summary
<h5>h5</h5>	<h5>h5</h5>	See summary
<h1>h1</h1><h2>h2</h2>	<h1>h1</h1><h2>h2</h2>	See summary
<code>code</code>	<code>code</code>	See summary
<pre>pre</pre>	<pre>pre</pre>	See summary
line<br/>break	line<br>break	See summary
<p>paragraph</p>	<p>paragraph</p>	See summary
<small>small</small>	<small>small</small>	See summary
<sup>sup</sup>	<sup>sup</sup>	See summary
<sub>sub</sub>	<sub>sub</sub>	See summary
<a href='https://funfedi.dev'>funfedi</a>	<a href="https://funfedi.dev" rel="nofollow noreferrer noopener" target="_blank">funfedi</a>	See summary
<script>alert('hi');</script>		See summary
<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />		See summary
wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	wbr: Fernstraßen<wbr>bau<wbr>privat<wbr>finanzierungs<wbr>gesetz	See summary
Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	Audio	See summary
Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	Video Video of a cow eating	See summary

summary	content	spoiler_text	Example
<b>bold</b>	<b>bold</b>	See summary
<strong>strong</strong>	<strong>strong</strong>	See summary
<i>italic</i>	<i>italic</i>	See summary
<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	See summary
<em>emphasis</em>	<em>emphasis</em>	See summary
<del>old</del><ins>new</ins>	<del>old</del><ins>new</ins>	See summary
<s>stricken</s>	<s>stricken</s>	See summary
<mark>mark</mark>	<mark>mark</mark>	See summary
find <var>x</var> (a variable)	find <var>x</var> (a variable)	See summary
<ol><li>ordered</li></ol>	<ol><li>ordered</li></ol>	See summary
<ul><li>unordered</li></ul>	<ul><li>unordered</li></ul>	See summary
<h1>h1</h1>	<h1>h1</h1>	See summary
<h2>h2</h2>	<h2>h2</h2>	See summary
<h3>h3</h3>	<h3>h3</h3>	See summary
<h4>h4</h4>	<h4>h4</h4>	See summary
<h5>h5</h5>	<h5>h5</h5>	See summary
<h1>h1</h1><h2>h2</h2>	<h1>h1</h1><h2>h2</h2>	See summary
<code>code</code>	<code>code</code>	See summary
<pre>pre</pre>	<pre>pre</pre>	See summary
line<br/>break	line<br/>break	See summary
<p>paragraph</p>	<p>paragraph</p>	See summary
<small>small</small>	<small>small</small>	See summary
<sup>sup</sup>	<sup>sup</sup>	See summary
<sub>sub</sub>	<sub>sub</sub>	See summary
<a href='https://funfedi.dev'>funfedi</a>	<a href='https://funfedi.dev'>funfedi</a>	See summary
<script>alert('hi');</script>	<script>alert('hi');</script>	See summary
<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />	<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />	See summary
wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	See summary
Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	See summary
Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	See summary

summary	content	spoiler_text	Example
<b>bold</b>	<b>bold</b>	See summary
<strong>strong</strong>	<strong>strong</strong>	See summary
<i>italic</i>	<i>italic</i>	See summary
<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	See summary
<em>emphasis</em>	<em>emphasis</em>	See summary
<del>old</del><ins>new</ins>	<del>old</del><ins>new</ins>	See summary
<s>stricken</s>	<s>stricken</s>	See summary
<mark>mark</mark>	<mark>mark</mark>	See summary
find <var>x</var> (a variable)	find <var>x</var> (a variable)	See summary
<ol><li>ordered</li></ol>	<ol><li>ordered</li></ol>	See summary
<ul><li>unordered</li></ul>	<ul><li>unordered</li></ul>	See summary
<h1>h1</h1>	<h1>h1</h1>	See summary
<h2>h2</h2>	<h2>h2</h2>	See summary
<h3>h3</h3>	<h3>h3</h3>	See summary
<h4>h4</h4>	<h4>h4</h4>	See summary
<h5>h5</h5>	<h5>h5</h5>	See summary
<h1>h1</h1><h2>h2</h2>	<h1>h1</h1><h2>h2</h2>	See summary
<code>code</code>	<code>code</code>	See summary
<pre>pre</pre>	<pre>pre</pre>	See summary
line<br/>break	line<br/>break	See summary
<p>paragraph</p>	<p>paragraph</p>	See summary
<small>small</small>	<small>small</small>	See summary
<sup>sup</sup>	<sup>sup</sup>	See summary
<sub>sub</sub>	<sub>sub</sub>	See summary
<a href='https://funfedi.dev'>funfedi</a>	<a href='https://funfedi.dev'>funfedi</a>	See summary
<script>alert('hi');</script>	<script>alert('hi');</script>	See summary
<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />	<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />	See summary
wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	See summary
Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	See summary
Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	See summary

summary	cw	Example
<b>bold</b>	<b>bold</b>
<strong>strong</strong>	<strong>strong</strong>
<i>italic</i>	<i>italic</i>
<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>
<em>emphasis</em>	<em>emphasis</em>
<del>old</del><ins>new</ins>	<del>old</del><ins>new</ins>
<s>stricken</s>	<s>stricken</s>
<mark>mark</mark>	<mark>mark</mark>
find <var>x</var> (a variable)	find <var>x</var> (a variable)
<ol><li>ordered</li></ol>	<ol><li>ordered</li></ol>
<ul><li>unordered</li></ul>	<ul><li>unordered</li></ul>
<h1>h1</h1>	<h1>h1</h1>
<h2>h2</h2>	<h2>h2</h2>
<h3>h3</h3>	<h3>h3</h3>
<h4>h4</h4>	<h4>h4</h4>
<h5>h5</h5>	<h5>h5</h5>
<h1>h1</h1><h2>h2</h2>	<h1>h1</h1><h2>h2</h2>
<code>code</code>	<code>code</code>
<pre>pre</pre>	<pre>pre</pre>
line<br/>break	line<br/>break
<p>paragraph</p>	<p>paragraph</p>
<small>small</small>	<small>small</small>
<sup>sup</sup>	<sup>sup</sup>
<sub>sub</sub>	<sub>sub</sub>
<a href='https://funfedi.dev'>funfedi</a>	<a href='https://funfedi.dev'>funfedi</a>
<script>alert('hi');</script>	<script>alert('hi');</script>
<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />	<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />
wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz
Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>
Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>

summary	content	spoiler_text	Example
<b>bold</b>		<h1>bold</h1>See summary
<strong>strong</strong>		<h1>strong</h1>See summary
<i>italic</i>		<h1>italic</h1>See summary
<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>		<h1>italic with. See Issue 142</h1>See summary
<em>emphasis</em>		<h1>emphasis</h1>See summary
<del>old</del><ins>new</ins>		<h1>oldnew</h1>See summary
<s>stricken</s>		<h1>stricken</h1>See summary
<mark>mark</mark>		<h1>mark</h1>See summary
find <var>x</var> (a variable)		<h1>find x (a variable)</h1>See summary
<ol><li>ordered</li></ol>		<h1>ordered</h1>See summary
<ul><li>unordered</li></ul>		<h1>unordered</h1>See summary
<h1>h1</h1>		<h1>h1</h1>See summary
<h2>h2</h2>		<h1>h2</h1>See summary
<h3>h3</h3>		<h1>h3</h1>See summary
<h4>h4</h4>		<h1>h4</h1>See summary
<h5>h5</h5>		<h1>h5</h1>See summary
<h1>h1</h1><h2>h2</h2>		<h1>h1h2</h1>See summary
<code>code</code>		<h1>code</h1>See summary
<pre>pre</pre>		<h1>pre</h1>See summary
line<br/>break		<h1>linebreak</h1>See summary
<p>paragraph</p>		<h1>paragraph</h1>See summary
<small>small</small>		<h1>small</h1>See summary
<sup>sup</sup>		<h1>sup</h1>See summary
<sub>sub</sub>		<h1>sub</h1>See summary
<a href='https://funfedi.dev'>funfedi</a>		<h1>funfedi</h1>See summary
<script>alert('hi');</script>		See summary
<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />		See summary
wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz		<h1>wbr: Fernstraßenbauprivatfinanzierungsgesetz</h1>See summary
Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>		<h1>Audio</h1>See summary
Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>		<h1>Video Video of a cow eating</h1>See summary

summary	content	spoiler_text	Example
<b>bold</b>	<b>bold</b>	See summary
<strong>strong</strong>	<strong>strong</strong>	See summary
<i>italic</i>	<i>italic</i>	See summary
<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	See summary
<em>emphasis</em>	<em>emphasis</em>	See summary
<del>old</del><ins>new</ins>	<del>old</del><ins>new</ins>	See summary
<s>stricken</s>	<s>stricken</s>	See summary
<mark>mark</mark>	<mark>mark</mark>	See summary
find <var>x</var> (a variable)	find <var>x</var> (a variable)	See summary
<ol><li>ordered</li></ol>	<ol><li>ordered</li></ol>	See summary
<ul><li>unordered</li></ul>	<ul><li>unordered</li></ul>	See summary
<h1>h1</h1>	<h1>h1</h1>	See summary
<h2>h2</h2>	<h2>h2</h2>	See summary
<h3>h3</h3>	<h3>h3</h3>	See summary
<h4>h4</h4>	<h4>h4</h4>	See summary
<h5>h5</h5>	<h5>h5</h5>	See summary
<h1>h1</h1><h2>h2</h2>	<h1>h1</h1><h2>h2</h2>	See summary
<code>code</code>	<code>code</code>	See summary
<pre>pre</pre>	<pre>pre</pre>	See summary
line<br/>break	line<br/>break	See summary
<p>paragraph</p>	<p>paragraph</p>	See summary
<small>small</small>	<small>small</small>	See summary
<sup>sup</sup>	<sup>sup</sup>	See summary
<sub>sub</sub>	<sub>sub</sub>	See summary
<a href='https://funfedi.dev'>funfedi</a>	<a href='https://funfedi.dev'>funfedi</a>	See summary
<script>alert('hi');</script>	<script>alert('hi');</script>	See summary
<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />	<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />	See summary
wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	See summary
Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	See summary
Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	See summary

summary	content	spoiler_text	Example
<b>bold</b>	<b>bold</b>	<p><span>See summary</span></p>
<strong>strong</strong>	<strong>strong</strong>	<p><span>See summary</span></p>
<i>italic</i>	<i>italic</i>	<p><span>See summary</span></p>
<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	<i>italic with.</i> See <a href="https://codeberg.org/helge/funfedidev/issues/142">Issue 142</a>	<p><span>See summary</span></p>
<em>emphasis</em>	<em>emphasis</em>	<p><span>See summary</span></p>
<del>old</del><ins>new</ins>	<del>old</del><ins>new</ins>	<p><span>See summary</span></p>
<s>stricken</s>	<s>stricken</s>	<p><span>See summary</span></p>
<mark>mark</mark>	<mark>mark</mark>	<p><span>See summary</span></p>
find <var>x</var> (a variable)	find <var>x</var> (a variable)	<p><span>See summary</span></p>
<ol><li>ordered</li></ol>	<ol><li>ordered</li></ol>	<p><span>See summary</span></p>
<ul><li>unordered</li></ul>	<ul><li>unordered</li></ul>	<p><span>See summary</span></p>
<h1>h1</h1>	<h1>h1</h1>	<p><span>See summary</span></p>
<h2>h2</h2>	<h2>h2</h2>	<p><span>See summary</span></p>
<h3>h3</h3>	<h3>h3</h3>	<p><span>See summary</span></p>
<h4>h4</h4>	<h4>h4</h4>	<p><span>See summary</span></p>
<h5>h5</h5>	<h5>h5</h5>	<p><span>See summary</span></p>
<h1>h1</h1><h2>h2</h2>	<h1>h1</h1><h2>h2</h2>	<p><span>See summary</span></p>
<code>code</code>	<code>code</code>	<p><span>See summary</span></p>
<pre>pre</pre>	<pre>pre</pre>	<p><span>See summary</span></p>
line<br/>break	line<br/>break	<p><span>See summary</span></p>
<p>paragraph</p>	<p>paragraph</p>	<p><span>See summary</span></p>
<small>small</small>	<small>small</small>	<p><span>See summary</span></p>
<sup>sup</sup>	<sup>sup</sup>	<p><span>See summary</span></p>
<sub>sub</sub>	<sub>sub</sub>	<p><span>See summary</span></p>
<a href='https://funfedi.dev'>funfedi</a>	<a href='https://funfedi.dev'>funfedi</a>	<p><span>See summary</span></p>
<script>alert('hi');</script>	<script>alert('hi');</script>	<p><span>See summary</span></p>
<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />	<img src="http://pasture-one-actor/assets/nlnet.png" alt="NLNET Logo" />	<p><span>See summary</span></p>
wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	wbr: Fernstraßen<wbr />bau<wbr />privat<wbr />finanzierungs<wbr />gesetz	<p><span>See summary</span></p>
Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	Audio <audio controls src="http://pasture-one-actor/assets/cow_moo.mp3"></audio>	<p><span>See summary</span></p>
Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	Video <video controls width="250"> <source src="http://pasture-one-actor/assets/cow_eating.mp4" type="video/mp4" /> Video of a cow eating</video>	<p><span>See summary</span></p>