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                <script src="" data-manual></script>

<h1>Syntax highlighting code blocks with Prism and the <a href="" target="_top">Custom Highlight API</a></h1>

<div class="warning"><p>Your browser does not support the Custom Highlight API. Please try Chrome 105+, Safari 17.2+, or Firefox Nightly</p></div>

<p>What if I told you you can syntax highlight code snippets without needing to overload the DOM with a ton of <code>&lt;span&gt;</code> elements wrapping each token in order to colorize them?</p>


<h3>Step 1: Declare your syntax highlighting color scheme</h3>

<p>The format is <code>::highlight(x)</code> where <code>x</code> is the type of token.</p>

<style visible>/* From prism.css */
::highlight(parameter) {
	color: #1a1a1a;

::highlight(comment), ::highlight(prolog), ::highlight(doctype), ::highlight(cdata) {
	color: slategray;

::highlight(punctuation) {
	color: #999;

::highlight(property), ::highlight(tag), ::highlight(boolean), ::highlight(number), ::highlight(constant), ::highlight(symbol), ::highlight(deleted), ::highlight(class-name) {
	color: #905;

::highlight(selector), ::highlight(attr-name), ::highlight(string), ::highlight(char), ::highlight(builtin), ::highlight(inserted) {
	color: #690;

::highlight(operator), ::highlight(entity), ::highlight(url) {
	color: #a67f59;
	background: hsla(0, 0%, 100%, 0.5);

::highlight(atrule), ::highlight(attr-value), ::highlight(keyword) {
	color: #07a;

::highlight(function) {
	color: #dd4a68;

::highlight(regex), ::highlight(important), ::highlight(variable) {
	color: #e90;

::highlight(important), ::highlight(bold) {
	font-weight: bold;

::highlight(italic) {
	font-style: italic;

::highlight(entity) {
	cursor: help;

<h3>Step 2: Register all token types as highlight styles</h3>
<script type="module" visible>if (CSS.highlights) {
	const tokenTypes = [ 'comment', 'prolog', 'doctype', 'cdata', 'punctuation', 'namespace',
	                     'property', 'tag', 'boolean', 'number', 'constant', 'symbol', 'deleted',
	                     'selector', 'attr', 'string', 'char', 'builtin', 'inserted', 'operator',
	                     'entity', 'url', 'string', 'atrule', 'attr', 'keyword', 'function', 'class',
	                     'regex', 'important', 'variable', 'important', 'bold', 'italic', 'entity',
	                     'parameter', 'class-name'];

	tokenTypes.forEach(tokenType => {
		CSS.highlights.set(tokenType, new Highlight());

<h3>Step 3: Tokenize the source code and register them with the highlights</h3>
<script type="module" visible>if (CSS.highlights) {
	const codeBlocks = document.querySelectorAll('script[visible], style[visible]');
	for (const codeBlock of codeBlocks) {
		// Tokenize it
		let tokens = Prism.tokenize(
			codeBlock.tagName == 'STYLE' ? Prism.languages.css : Prism.languages.javascript

		// Loop all tokens and highlight them based on their type
		let pos = 0;
		for (const token of tokens) {
			if (token.type) {
				const range = new Range();
				range.setStart(codeBlock.firstChild, pos);
				range.setEnd(codeBlock.firstChild, pos + token.length);
				CSS.highlights.get(token.alias ?? token.type)?.add(range);
			pos += token.length;


<p>This page acts as its own demo: the CSS and JavaScript you see here is the actual code that gets executed and thereby syntax highlighted.</p>

<h2>Need more info?</h2>

<p>Go read <a href="" target="_top"></a> which hold a full write-up on this (and more)</p>


                @layer reset, layout;

@layer layout {
	@layer general {
		html {
			font-family: sans-serif;
		body {
			padding: 3rem 0 10rem;
			width: 90%;
			max-width: 50em;
			margin: 0 auto;
		h2 {
			margin-top: 2em;
		a {
			color: #0000aa;
			text-decoration: none;
			&:hover {
				color: blue;
		footer {
			text-align: center;
			font-style: italic;
			margin: 4em 0;

	@layer code {
		pre {
			display: block;
			white-space: pre;
			border: 1px solid #dedede;
			padding: 1em;
			background: #fafafa;
			font-family: ui-monospace, SFMono-Regular, SF Mono, Menlo, Consolas,
				Liberation Mono, monospace;
			overflow-x: auto;
			border-left: 0.4em solid cornflowerblue;
			tab-size: 2;
			color: #1a1a1a;
			line-height: 1.6;

		code:not(pre code), /* output:not(code:has(output) output) */ {
			background: #f7f7f7;
			border: 1px solid rgb(0 0 0 / 0.2);
			padding: 0.1rem 0.3rem;
			margin: 0.1rem 0;
			border-radius: 0.2rem;
			display: inline-block;

	@layer warning {
		.warning {
			display: none;
			box-sizing: border-box;
			padding: 1em;
			margin: 1em 0;
			border: 1px solid #ccc;
			background: rgba(255 255 205 / 0.8);

		.warning > :first-child {
			margin-top: 0;

		.warning > :last-child {
			margin-bottom: 0;

		.warning a {
			color: blue;
		.warning--info {
			border: 1px solid #123456;
			background: rgb(205 230 255 / 0.8);
		.warning--alarm {
			border: 1px solid red;
			background: #ff000010;

@layer reset {
	* {
		box-sizing: border-box;
	body {
		margin: 0;
		padding: 0;



                if (!CSS.highlights) {
	document.querySelector('.warning').style.display = 'block';