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Extending Lion Documentation

If you extend Lion components, you don't only want to reuse the components, but you probably want to reuse the documentation (Storybook demos) as well. Wouldn't it be nice to just take it all from lion, but replace it with your own design system extension, so you don't have the extra maintenance of essentially copying the docs from Lion for your own design system implementation?

In this blog we will explain how Lion supports this use case, and allows you to extend not just the components, but also the documentation.

Important to note is that you must have a naming convention in your extension that is similar to Lion* for class names and lion-* for tag names, e.g. LeaTabs and lea-tabs. So essentially, have a consistent prefix for all your extension classes and tagnames.

Steps involved

In order to extend documentation, there are a few things that we need to enable you to do:

  1. Control which documentation MD files you extend, and which you leave out entirely. Because perhaps LionTabs is the only component that you extend.
  2. Support codified demos but replace the Lion component with the design system component equivalent. This means that the import paths for the component need to be altered to the path where your design system component lives.
  3. Allow to create overrides for the documentation. If we reference lion-tabs, but your tabs is called lea-tabs, you should be able to replace this piece of text easily. Or maybe we reference that amongst a list of browsers, we support IE11, but your design system doesn't. Then it should be easy to remove that piece of text from your extension docs.
  4. Allow to remove sections of documentation from Lion, add sections, and replace sections easily.

Lastly, it needs to be possible for this to work locally (when running Storybook prebuilt using es-dev-server) as well as in production (when building the full storybook with rollup and deploying it).

Storybook Main file

For step 1, we can use @open-wc/demoing-storybook version 2 or higher, which uses Prebuilt Storybook with MDJS. Using this is a prerequisite for the rest of this blog.

Install it manually (and see the docs for configuring):

npm i @open-wc/demoing-storybook --save-dev

Or scaffold it with basic configuration by doing

npm init @open-wc

And adding/upgrading Demoing.

Now we need to specify in our .storybook/main.js which stories to load, as well as specifying some es-dev-server configuration options. Only nodeResolve is required, but watch and open are a nice bonus!

module.exports = {
  stories: ['../node_modules/@lion/tabs/', '../packages/**/!(*.override)*.md'],
  esDevServer: {
    nodeResolve: true,
    watch: true,
    open: true,

Later in this blog in the Adjust Documentation section we will explain about why we exclude * files here, since they are used for specific overrides and not to be included as independent story files. This file name syntax is configurable.

So here we only extend the documentation of LionTabs, for our own LeaTabs. But our repository is a monorepository with multiple other packages that don't use Lion, which we want to include as well, so we also add the second line to include those.

This step alone should already give you the LionTabs docs inside your own Storybook, but not yet transformed to your LeaTabs extension of it, which we will explain next.

Replacing imports and tagnames

Analysing paths

Potentially the hardest part is to analyse your extension LeaTabs, and to figure out how we should transform the import paths for LionTabs to new paths to your LeaTabs.

To do this we make use of Providence. This tool has a command that creates a full map of all the import paths of a reference project (Lion) and can replace them with the correct paths of a target project (Lea).

So lets install it:

npm i providence-analytics --save-dev

And to use it, let's add a script to your projects package.json:

"scripts": {
  "providence:extend": "providence extend-docs -r 'node_modules/@lion/*' --prefix-from lion --prefix-to lea"

The --prefix-from and --prefix-to are the prefixes of the project you extend from (most of the times lion) and your own projects prefix (in this case lea). For classnames it will look for Lion* and Lea* respectively, for tagnames it will look for lion-* and lea-* respectively.

If you know you only use a single component from lion, you can reduce the time the tool needs for analysis, by specifying this package -r 'node_modules/@lion/tabs'.

Running the script will create a providence-extend-docs-data.json file, with all from/to information. You can change the name / location of the output file, refer to Providence Documentation for this.

Running it automatically when upgrading lion dependency

Inside ING, our design system also makes use of this providence tool to create this data JSON file. But since the analysis takes a few minutes, we only run it, automatically, when we upgrade our lion dependencies. We do this with the following two package.json scripts:

"scripts": {
  "upgrade:lion": "npm upgrade --scope @lion --latest --exact && npm run providence:extend",
  "providence:extend": "providence extend-docs -r 'node_modules/@lion/*' --prefix-from lion --prefix-to ing"

Replacing paths & template tagnames

Now that we have a JSON file with all the information we need to know about to replace import paths and tagnames inside templates, we can start transforming the LionTabs documentation to LeaTabs documentation.

For this, we created a babel-plugin called babel-plugin-extend-docs.

This will analyse the JavaScript script and story content inside the markdown files, which uses MDJS syntax, and transform it on the fly in es-dev-server, as well as on rollup build for production.

So all you need to do is to install this plugin:

npm i babel-plugin-extend-docs --save-dev

and create a babel.config.js file in the root of your project:

const path = require('path');
const providenceExtendConfig = require('./providence-extend-docs-data.json');

const extendDocsConfig = {
  rootPath: path.resolve('.'),
  changes: providenceExtendConfig,

module.exports = {
  overrides: [
      test: ['./node_modules/@lion/*/', './node_modules/@lion/*/docs/*.md'],
      plugins: [['babel-plugin-extend-docs', extendDocsConfig]],

As you can see, we import the providence output file and pass it to the plugin options as the changes property.

Now, the babel plugin will run for the files that we specify in test property, and replace the imports properly, as well as the tag names inside JavaScript code snippets!

For the JavaScript code snippets, it only transforms the ones that use MDJS syntax, e.g. ```js script, ```js story and ```js preview-story

To ensure babel actually runs for your Storybook, you will have to add it to your es-dev-server configuration:


module.exports = {
  stories: ['../node_modules/@lion/tabs/', '../packages/**/!(*.override)*.md'],
  esDevServer: {
    nodeResolve: true,
    watch: true,
    open: true,
    babel: true,

You should now see the LionTabs instances transformed into your own LeaTabs!

Adjust documentation content

In some cases you don't want to show all examples of how to use a component. Sometimes information is Lion specific, or perhaps in your design system you are not allowed to use a certain feature that we documented in Lion.

In our example, we will show you have to remove the Rationale section that you would normally inherit from the Lion documentation.

For this step we make use of a remark plugin for the MD content, similar to how you would use a babel plugin for JS content. It is called Remark extend. It will let you add, remove or replace sections or specific words.

First of all we need to add the plugin to the .storybook/main.js:

const fs = require('fs');
const { remarkExtend } = require('remark-extend');

function isLion(filePath) {
  return filePath.indexOf('@lion/') !== -1;

function getLocalOverridePath(filePath, root = process.cwd()) {
  const rel = filePath.substring(filePath.indexOf('/@lion/') + 7, filePath.length - 3);
  return `${root}/packages/${rel}`;

module.exports = {
  setupMdjsPlugins: (plugins, filePath) => {
    if (!isLion(filePath)) {
      return plugins;
    const newPlugins = [...plugins];
    const markdownIndex = newPlugins.findIndex(plugin => === 'markdown');
    const overridePaths = [getLocalOverridePath(filePath), `${process.cwd()}/.storybook/`];

    let i = 0;
    for (const overridePath of overridePaths) {
      if (fs.existsSync(overridePath)) {
        const extendMd = fs.readFileSync(overridePath, 'utf8');
        newPlugins.splice(markdownIndex, 0, {
          name: `remarkExtend${i}`,
          plugin: remarkExtend.bind({}),
          options: { extendMd, filePath, overrideFilePath: overridePath },
      i += 1;
    return newPlugins;

In the code above we have 2 places in where you can do overrides: ./.storybook/ for generic overrides and via getLocalOverridePath for each component, when needed, the rel needs to be the same in lion and your own project to be able to override the right file.

We insert a remarkExtend plugin instance for both the local overrides and the global overrides, and pass the necessary arguments. Then we return the new array of plugins for Mdjs.

In each file you need to add a specifier which section you want to override. As a first step we want to load lea-tab and lea-tab-panel also in the project. We need to add some imports to the top of the file.

Use triple backtick ` to create a fenced codeblock ```, and put inside it:


Then below that, create another fenced codeblock with js script annotation with your imports inside it:

import '../lea-tab.js';
import '../lea-tab-panel.js';

And then replace each reference to lion-tab with lea-tab inside the documentation content, this also covers lion-tab and lion-tab-panel. We exclude JS snippets 'nodes', those are handled by the babel plugin already.

Create another fenced codeblock with js ::replaceFrom(':root') annotation:

module.exports.replaceSection = node => {
  if (node.type !== 'code' && node.value) {
    let newCode = node.value;
    newCode = newCode.replace(/lion-tab/g, 'lea-tab');
    node.value = newCode;
  return node;

You can remove content as well. Create a fenced codeblock:

::removeFrom('heading:has([value=Distribute New Elements])')

Or you can add an extra paragraph below the content. Create a fenced codeblock:


See Remark extend for more information

Lea Tabs Special Feature

export const specialFeature = () =>
      <lea-tab slot="tab">Info</lea-tab>
      <lea-tab-panel slot="panel"> Info page with lots of information about us. </lea-tab-panel>
      <lea-tab slot="tab">Work</lea-tab>
      <lea-tab-panel slot="panel"> Work page that showcases our work. </lea-tab-panel>


Writing good extensive documentation is hard and time consuming, so being able to extend not only the code, but also the documentation will increase your work speed.

We showed you how to set it up and how you can adjust the documentation to fit your extended component.

And since this can be achieved with 3 separate tools, you can also use it to extend other documentation.