L4 - Rules as Code - Legal language syntax highlighting for Highlight.js

January 30, 2026 · View on GitHub

L4 is a functional programming language created by Legalese to help write digital-first policies, contracts and legislation.

Usage

Simply include the Highlight.js library in your webpage or Node app, then load this module.

Static website or simple usage

Simply load the module after loading Highlight.js. You'll use the minified version found in the dist directory. This module is just a CDN build of the language, so it will register itself as the Javascript is loaded.

<script type="text/javascript" src="/path/to/highlight.min.js"></script>
<script type="text/javascript" charset="UTF-8"
  src="/path/to/highlightjs-l4/dist/l4.min.js"></script>
<script type="text/javascript">
  hljs.highlightAll();
</script>

With Node or another build system

If you're using Node / Webpack / Rollup / Browserify, etc, simply require the language module, then register it with Highlight.js.

var hljs = require('highlightjs');
var hljsL4 = require('highlightjs-l4');

hljs.registerLanguage("l4", hljsL4);
hljs.highlightAll();

React

You need to import both Highlight.js and third-party language highlighter like this one for L4:

import React, {Component} from 'react'
import 'l4-rules.css' // or your favourite theme
import hljsL4 from 'l4.js'
import hljs from 'highlight.js'
hljs.registerLanguage('l4', hljsL4);

class Highlighter extends Component
{
  constructor(props)
  {
    super(props);
    hljs.highlightAll();
  }

  render()
  {
    let {children} = this.props;
    return
    {
      <pre ref={(node) => this.node = node}>
        <code className="l4">
          {children}
        </code>
      </pre>
    }
  }
}

export default Highlighter;

License

Highlight.js is released under the BSD 3-Clause License. See LICENSE file for details. highlightjs-l4 is released under the Apache-2.0 License. See LICENSE file for details.

Author

Thomas Gorissen thomas@legalese.com