Theme adapters

Theme adapters reuse styles from Highlight.js, Prism, or TextMate while Alto continues to parse and render source code on the server. They do not load a client-side highlighter and do not add languages.

Prefer local theme files in production. The fromFile() factories validate that a path exists, refers to a regular file, and is readable.

Highlight.js CSS

<?php

declare(strict_types=1);

require __DIR__.'/vendor/autoload.php';

use Alto\Code\Highlight\Adapter\HighlightJsThemeAdapter;
use Alto\Code\Highlight\Highlighter;

$theme = HighlightJsThemeAdapter::fromFile(
    __DIR__.'/themes/github-dark.css',
    isDark: true,
);
$highlighter = new Highlighter($theme);

echo '<style>'.$theme->getStylesheet().'</style>';
echo $highlighter->highlight('<?php echo "Hello";', 'php');

The adapter maps Alto semantic scopes to hljs-* classes, adapts the CSS selectors to Alto's markup, and adds the hljs class to the generated <code> element.

Prism CSS

<?php

declare(strict_types=1);

require __DIR__.'/vendor/autoload.php';

use Alto\Code\Highlight\Adapter\PrismThemeAdapter;
use Alto\Code\Highlight\Highlighter;

$theme = PrismThemeAdapter::fromFile(
    __DIR__.'/themes/prism-tomorrow.css',
    isDark: true,
);
$highlighter = new Highlighter($theme);

echo '<style>'.$theme->getStylesheet().'</style>';
echo $highlighter->highlight('const answer = 42;', 'javascript');

The adapter maps semantic scopes to Prism's token classes. Alto emits language-* classes on its <pre> and <code> elements, so normal Prism theme selectors can apply without running Prism JavaScript.

TextMate .tmTheme

<?php

declare(strict_types=1);

require __DIR__.'/vendor/autoload.php';

use Alto\Code\Highlight\Adapter\TextMateThemeAdapter;
use Alto\Code\Highlight\Highlighter;

$theme = TextMateThemeAdapter::fromFile(
    __DIR__.'/themes/monokai.tmTheme',
    isDark: true,
);
$highlighter = new Highlighter($theme);

echo '<style>';
echo '.alto-highlight { padding: 1rem; overflow-x: auto; background: #272822; }';
echo $theme->getStylesheet();
echo '</style>';
echo $highlighter->highlight('SELECT * FROM users;', 'sql');

The adapter parses the PList XML, maps recognized TextMate scopes to Alto scopes, and generates alto-tm-* classes. TextMate use requires PHP's SimpleXML extension. Add your own .alto-highlight container rule when the generated stylesheet does not provide background, spacing, or overflow.

Dark-mode metadata

The isDark argument records theme metadata returned by ThemeInterface::isDark(). It does not inspect the source file or alter its colors. Pass the value that matches the chosen theme.

Remote constructors

HighlightJsThemeAdapter and PrismThemeAdapter constructors can fetch named themes from their configured CDN when no local CSS path is supplied. If a fetch fails, their stylesheet falls back to a CSS @import. This makes output dependent on network access, so fromFile() is the deterministic choice for production and documentation builds.

Styling boundaries

Adapters translate style classes only:

• parsing remains entirely in Alto;
• supported language identifiers remain those in the active highlighter;
• source escaping and output structure remain Alto's responsibility;
• line numbers still use alto-line-number and alto-highlighted.

See Languages, Getting started, and Creating a theme for those separate contracts.