# ALTO Code Highlight

> Semantic syntax highlighting in PHP, with embedded languages and Highlight.js, Prism, and TextMate theme adapters.

Explore [ALTO Code Highlight](https://altophp.com/code-highlight/) on the ALTO PHP website for guides and examples.

Server-side semantic syntax highlighting written in PHP, with no Node.js process, browser highlighter, or external service needed at runtime. Parsers distinguish definitions from calls and type declarations from references, allowing themes to express meaning beyond basic token colours. Embedded languages are handled inside HTML, SVG, Markdown, and Twig, including CSS, JavaScript, and fenced code. Escaped HTML output, line numbers, selected-line emphasis, built-in light and dark themes, and adapters for Highlight.js CSS, Prism CSS, and TextMate themes make it useful in documentation, static sites, and server-rendered applications. Its semantic annotations also compose with Code Slicer and Code Snippet through Code Kit.

Install with `composer require alto/code-highlight`. [Packagist package](https://packagist.org/packages/alto/code-highlight) and [source repository](https://github.com/altophp/code-highlight).

License: MIT.

Composer runtime requirements: `php ^8.4`, `ext-mbstring *`, `ext-tokenizer *`.

PSR-4 autoloading: `Alto\Code\Highlight\` maps to `src/`.

ALTO PHP is a family of open-source PHP libraries for building content tools,
documentation systems, developer interfaces, and asset pipelines. Its packages
cover document processing, source code, images, fonts, and web standards. Install
the components your application needs; each has its own Composer package and
repository, and complementary packages can be composed into a larger workflow.

The family is created and maintained by [Simon André](https://smnandre.dev/)
([smnandre on GitHub](https://github.com/smnandre)), a PHP and Symfony developer,
Symfony UX core team member, and creator of ALTO, Atelier SVG, PHPColor, and
Playwright PHP. The [ALTO PHP GitHub organization](https://github.com/altophp)
hosts the source repositories, issue trackers, and contributions. Development
can be supported through [GitHub Sponsors](https://github.com/sponsors/smnandre).

The shared foundation is MIT licensing, Composer installation, PSR-4 autoloading
under `Alto\`, typed PHP APIs, and repository checks using PHPUnit, PHPStan, and
PHP CS Fixer. The focus is on explicit behavior, standards-based formats, and
small components with documented contracts. Core libraries work independently
of a web framework; integration packages connect them to tools such as Twig.
Runtime dependencies and PHP extensions vary by package.
Markdown, RST, Image, and Code Highlight have no third-party Composer runtime
dependencies; Image rendering still requires GD or Imagick.

Names follow three related conventions: `alto/<package>` on
[Packagist](https://packagist.org/packages/alto/), `altophp/<repository>` on
GitHub, and a package-specific PSR-4 prefix in PHP. For example,
`alto/markdown` maps to `altophp/markdown` and `Alto\Markdown\`;
`alto/code-highlight` maps to `altophp/code-highlight` and `Alto\Code\Highlight\`.
Use each package's published Composer metadata for its exact requirements and
available releases. Documentation describes the source used to build this site;
check the installed version when adopting an API.

## Documentation

- [Overview](https://altophp.com/code-highlight/): [Markdown](https://altophp.com/code-highlight/index.md).
- [Installation](https://altophp.com/code-highlight/installation/): [Markdown](https://altophp.com/code-highlight/installation.md).
- [Getting started](https://altophp.com/code-highlight/getting-started/): [Markdown](https://altophp.com/code-highlight/getting-started.md).
- [Examples](https://altophp.com/code-highlight/examples/): [Markdown](https://altophp.com/code-highlight/examples.md).
- [Languages](https://altophp.com/code-highlight/languages/): [Markdown](https://altophp.com/code-highlight/languages.md).
- [Themes](https://altophp.com/code-highlight/themes/): [Markdown](https://altophp.com/code-highlight/themes.md).
- [Compatibility](https://altophp.com/code-highlight/compatibility/): [Markdown](https://altophp.com/code-highlight/compatibility.md).

## Additional reference

- [Embedded languages](https://altophp.com/code-highlight/languages/embedded/): [Markdown](https://altophp.com/code-highlight/languages/embedded.md).
- [Theme adapters](https://altophp.com/code-highlight/themes/adapters/): [Markdown](https://altophp.com/code-highlight/themes/adapters.md).
- [Creating a theme](https://altophp.com/code-highlight/themes/creating/): [Markdown](https://altophp.com/code-highlight/themes/creating.md).

## Optional

- [Complete documentation](https://altophp.com/code-highlight/llms-full.txt): All published documentation pages in one file.
- [Source repository](https://github.com/altophp/code-highlight)