Front Matter Extension

The FrontMatterExtension adds the ability to parse YAML front matter from the Markdown document and include that in the return result.

Installation

This extension is bundled with league/commonmark. This library can be installed via Composer:

composer require league/commonmark

See the installation section for more details.

You will also need to install symfony/yaml or the YAML extension for PHP to use this extension. For symfony/yaml:

composer require symfony/yaml

(You can use any version of symfony/yaml 2.3 or higher, though we recommend using 4.0 or higher.)

Front Matter Syntax

This extension follows the Jekyll Front Matter syntax. The front matter must be the first thing in the file and must take the form of valid YAML set between triple-dashed lines. Here is a basic example:

---
layout: post
title: I Love Markdown
tags:
  - test
  - example
---

# Hello World!

This will produce a front matter array similar to this:

$parsedFrontMatter = [
    'layout' => 'post',
    'title' => 'I Love Markdown',
    'tags' => [
        'test',
        'example',
    ],
];

And the HTML output will only contain the one heading:

<h1>Hello World!</h1>

Usage

Configure your Environment as usual and add the FrontMatterExtension:

use League\CommonMark\Environment\Environment;
use League\CommonMark\Extension\CommonMark\CommonMarkCoreExtension;use League\CommonMark\Extension\FrontMatter\FrontMatterExtension;
use League\CommonMark\Extension\FrontMatter\Output\RenderedContentWithFrontMatter;
use League\CommonMark\MarkdownConverter;

// Define your configuration, if needed
$config = [];

// Configure the Environment with all the CommonMark parsers/renderers
$environment = new Environment($config);
$environment->addExtension(new CommonMarkCoreExtension());

// Add the extension
$environment->addExtension(new FrontMatterExtension());

// Instantiate the converter engine and start converting some Markdown!
$converter = new MarkdownConverter($environment);

// A sample Markdown file with some front matter:
$markdown = <<<MD
---
layout: post
title: I Love Markdown
tags:
  - test
  - example
---

# Hello World!
MD;

$result = $converter->convertToHtml($markdown);

// Grab the front matter:
if ($result instanceof RenderedContentWithFrontMatter) {
    $frontMatter = $result->getFrontMatter();
}

// Output the HTML using any of these:
echo $result;               // implicit string cast
// or:
echo (string) $result;      // explicit string cast
// or:
echo $result->getContent();

Parsing Front Matter Only

You don’t have to parse the entire file (including all the Markdown) if you only want the front matter. You can either instantiate the front matter parser yourself and call it directly, like this:

use League\CommonMark\Extension\FrontMatter\Data\LibYamlFrontMatterParser;
use League\CommonMark\Extension\FrontMatter\Data\SymfonyYamlFrontMatterParser;
use League\CommonMark\Extension\FrontMatter\FrontMatterParser;

$markdown = '...'; // TODO: Load some Markdown content somehow

// For `symfony/yaml`
$frontMatterParser = new FrontMatterParser(new SymfonyYamlFrontMatterParser());
// For YAML extension
$frontMatterParser = new FrontMatterParser(new LibYamlFrontMatterParser());
$result = $frontMatterParser->parse($markdown);

var_dump($result->getFrontMatter()); // The parsed front matter
var_dump($result->getContent()); // Markdown content without the front matter

Or you can use the getFrontMatterParser() method from the extension:

use League\CommonMark\Extension\FrontMatter\FrontMatterExtension;

$markdown = '...'; // TODO: Load some Markdown content somehow

$frontMatterExtension = new FrontMatterExtension();
$result = $frontMatterExtension->getFrontMatterParser()->parse($markdown);

var_dump($result->getFrontMatter()); // The parsed front matter
var_dump($result->getContent()); // Markdown content without the front matter

This latter approach may be more convenient if you have already instantiated a FrontMatterExtension object you’re adding to the Environment somewhere and just want to call that.


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