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html-tags.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>HTML tags and trailing slashes</title>
<style>
:root {
--border-code: aliceblue;
}
body {
margin: 4em;
line-height: 1.5;
max-width: 40em;
}
@media (width < 34em) {
body {
margin: 1em;
}
}
@media (prefers-color-scheme: dark) {
:root {
--border-code: #484c4e;
}
body {
background-color: hsl(240, 12%, 16%);
color: hsl(200, 10%, 94%);
}
a { color: #a2cffe; }
a:visited { color: #ca9bf7; }
}
p, li {
margin-block: 2.25em;
}
h3 + p {
margin-block-start: 2.75em;
}
ol {
padding-inline-start: 2ch;
}
li {
padding-inline-start: 0.5ch;
}
pre {
padding: 2ch;
padding-inline: 2.5ch;
border: 1px solid var(--border-code);
overflow-x: auto;
}
li > pre {
margin-inline-start: -2.5ch;
}
:not(pre) > code {
padding: 0.5ch;
border: 1px solid var(--border-code);
}
blockquote {
margin: 0;
}
blockquote p {
margin-block: 1ch;
}
div.listing > p {
margin-block-end: 1.5rem;
}
div.listing > pre {
white-space: wrap;
}
</style>
</head>
<body>
<h3>HTML tags and trailing slashes</h3>
<p>
XML's foray into HTML, XHTML, has long ended but left a confusing detritus of
trailing slashes and their legality behind. The smog of JSX compounds
visibility. But once we leave behind the rubble and the haze, the situation is
clear.
</p>
<p>HTML has only two† kinds of elements††:</p>
<ol>
<li>
Normal elements. These must have a closing tag, even if they have no child
content.
<pre><code><div></div>
<button></button>
</code></pre>
</li>
<li>
Void elements. This should not have a closing tag, since they can not have any
content.
<pre><code><img>
<br>
</code></pre>
</li>
</ol>
<blockquote>
<small>
<p>
† to first approximation. The <a
href="https://html.spec.whatwg.org/multipage/syntax.html#void-elements">spec</a>
lists 6.
</p>
<p>
†† <em>elements</em> are the things themselves, while <em>tags</em> delimit
their start and end.
</p>
</small>
</blockquote>
<p>
The self closing shortcut for elements without child content, e.g.
<code><div /></code> is not valid even if it may work.
</p>
<p>
<em><b>tldr</b></em> If you're writing HTML, close your tags (explicitly, not
self-closingly), even if there is no content, unless it is a void element.
</p>
<div class="listing">
<p>These are the void elements:</p>
<pre><code>area, base, br, col, embed, hr, img, input, link, meta, source, track, wbr
</code></pre>
</div>
</body>
</html>