PHP Markdown

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PHP Markdown Lib 2.0.0 (131 KB): Library package for developers. Requires PHP 7.4 or later. Also available on Packagist et and Github. September 26, 2022.

The old classic version that works as a plugin for WordPress and Smarty is no longer supported.

Introduction

This is a library package that includes the PHP Markdown parser and its sibling PHP Markdown Extra with additional features. Originally it was a port to PHP of the Markdown tool written by John Gruber.

“Markdown” is two things: a plain text markup syntax, and a software tool that converts the plain text markup to HTML for publishing on the web.

The Markdown syntax allows you to write text naturally and format it without using HTML tags. More importantly: in Markdown format, your text stays enjoyable to read for a human being, and this is true enough that it makes a Markdown document publishable as-is, as plain text. If you are using text-formatted email, you already know some part of the syntax.

Visit the Concepts page for a short introduction full of examples where you will learn to write with Markdown. If you have some understanding of HTML, you can also read the full documentation of Markdown’s syntax, available on John’s web site.

Requirement

This library package requires PHP 5.3 or later.

Note: The older plugin/library hybrid package for PHP Markdown and PHP Markdown Extra is still maintained and will work with PHP 4.0.5 and later.

Before PHP 5.3.7, pcre.backtrack_limit defaults to 100 000, which is too small in many situations. You might need to set it to higher values. Later PHP releases defaults to 1 000 000, which is usually fine.

Usage

This library package is meant to be used with class autoloading. For autoloading to work, your project needs have setup a PSR-0-compatible autoloader. See the included Readme.php file for a minimal autoloader setup. (If you cannot use autoloading, see below.)

With class autoloading in place, putting the ‘Michelf’ folder in your include path should be enough for this to work:

use Michelf\Markdown;
$my_html = Markdown::defaultTransform($my_text);

Markdown Extra syntax is also available the same way:

use Michelf\MarkdownExtra;
$my_html = MarkdownExtra::defaultTransform($my_text);

If you wish to use PHP Markdown with another text filter function built to parse HTML, you should filter the text after the transform function call. This is an example with [PHP SmartyPants][psp]:

use Michelf\Markdown, Michelf\SmartyPants;
$my_html = Markdown::defaultTransform($my_text);
$my_html = SmartyPants::defaultTransform($my_html);

All these examples are using the static defaultTransform static function found inside the parser class. If you want to customize the parser configuration, you can also instantiate it directly and change some configuration variables:

use Michelf\MarkdownExtra;
$parser = new MarkdownExtra;
$parser->fn_id_prefix = "post22-";
$my_html = $parser->transform($my_text);

To learn more, see the full list of configuration variables.

Usage without an autoloader

If you cannot use class autoloading, you can still use include or require to access the parser. To load the Michelf\Markdown parser, do it this way:

require_once 'Michelf/Markdown.inc.php';

Or, if you need the Michelf\MarkdownExtra parser:

require_once 'Michelf/MarkdownExtra.inc.php';

While the plain .php files depend on autoloading to work correctly, using the .inc.php files instead will eagerly load the dependencies that would be loaded on demand if you were using autoloading.

Public API and Versioning Policy

Version numbers are of the form major.minor.patch.

The public API of PHP Markdown consist of the two parser classes Markdown and MarkdownExtra, their constructors, the transform and defaultTransform functions and their configuration variables. The public API is stable for a given major version number. It might get additions when the minor version number increments.

Protected members are not considered public API. This is unconventional and deserves an explanation. Incrementing the major version number every time the underlying implementation of something changes is going to give nonessential version numbers for the vast majority of people who just use the parser. Protected members are meant to create parser subclasses that behave in different ways. Very few people create parser subclasses. I don’t want to discourage it by making everything private, but at the same time I can’t guarantee any stable hook between versions if you use protected members.

Syntax changes will increment the minor number for new features, and the patch number for small corrections. A new feature is something that needs a change in the syntax documentation. Note that since PHP Markdown Lib includes two parsers, a syntax change for either of them will increment the minor number. Also note that there is nothing perfectly backward-compatible with the Markdown syntax: all inputs are always valid, so new features always replace something that was previously legal, although generally nonsensical to do.

Bugs

To file bug reports please use the issue tracker or send an email to: michel.fortin@michelf.ca

Please include with your report: (1) the example input; (2) the output you expected; (3) the output PHP Markdown actually produced.

If you have a problem where Markdown gives you an empty result, first check that the backtrack limit is not too low by running php --info | grep pcre. See Installation and Requirement above for details.

Development and Testing

See the PHP Markdown repository on Github.

Pull requests for fixing bugs are welcome. Proposed new features are going meticulously reviewed — taking into account backward compatibility, potential side effects, and future extensibility — before deciding on acceptance or rejection.

If you make a pull request that includes changes to the parser please add tests for what is being changed to MDTest and make a pull request there too.

Copyright and License

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
Neither the name “Markdown” nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

This software is provided by the copyright holders and contributors “as is” and any express or implied warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose are disclaimed. In no event shall the copyright owner or contributors be liable for any direct, indirect, incidental, special, exemplary, or consequential damages (including, but not limited to, procurement of substitute goods or services; loss of use, data, or profits; or business interruption) however caused and on any theory of liability, whether in contract, strict liability, or tort (including negligence or otherwise) arising in any way out of the use of this software, even if advised of the possibility of such damage.