Markdown

Markdown[9] is a lightweight markup language for creating formatted text using a plain-text editor. John Gruber created Markdown in 2004 as a markup language that is easy to read in its source code form.[9] Markdown is widely used for blogging and instant messaging, and also used elsewhere in online forums, collaborative software, documentation pages, and readme files.

For the marketing term, see Price markdown.
Markdown
Filename extensions
.md, .markdown[1][2]
Internet media typetext/markdown[2]
Uniform Type Identifier (UTI)net.daringfireball.markdown
Developed byJohn Gruber
Initial releaseMarch 9, 2004 (2004-03-09)[3][4]
Latest release
1.0.1
December 17, 2004 (2004-12-17)[5]
Type of formatOpen file format[6]
Extended topandoc, MultiMarkdown, Markdown Extra, CommonMark,[7] RMarkdown[8]
Websitedaringfireball.net/projects/markdown/

The initial description of Markdown[10] contained ambiguities and raised unanswered questions, causing implementations to both intentionally and accidentally diverge from the original version. This was addressed in 2014 when long-standing Markdown contributors released CommonMark, an unambiguous specification and test suite for Markdown.[11]

History

Markdown was inspired by pre-existing conventions for marking up plain text in email and usenet posts, such as the earlier markup languages setext (c. 1992), Textile (c. 2002), and reStructuredText (c. 2002).[9]

In 2002 Aaron Swartz created atx and referred to it as "the true structured text format". Gruber created the Markdown language in 2004, with Swartz acting as beta tester,[3][4] with the goal of enabling people "to write using an easy-to-read and easy-to-write plain text format, optionally convert it to structurally valid XHTML (or HTML)."[5]

Its key design goal was readability, that the language be readable as-is, without looking like it has been marked up with tags or formatting instructions,[9] unlike text formatted with 'heavier' markup languages, such as Rich Text Format (RTF), HTML, or even wikitext (each of which have obvious in-line tags and formatting instructions which can make the text more difficult for humans to read).

Gruber wrote a Perl script, Markdown.pl, which converts marked-up text input to valid, well-formed XHTML or HTML and replaces angle brackets (<, >) and ampersands (&) with their corresponding character entity references. It can take the role of a standalone script, a plugin for Blosxom or a Movable Type, or of a text filter for BBEdit.[5]

Rise and divergence

As Markdown's popularity grew rapidly, many Markdown implementations appeared, driven mostly by the need for additional features such as tables, footnotes, definition lists,[note 1] and Markdown inside HTML blocks.

The behavior of some of these diverged from the reference implementation, as Markdown was only characterised by an informal specification[14] and a Perl implementation for conversion to HTML.

At the same time, a number of ambiguities in the informal specification had attracted attention.[15] These issues spurred the creation of tools such as Babelmark[16][17] to compare the output of various implementations,[18] and an effort by some developers of Markdown parsers for standardisation. However, Gruber has argued that complete standardization would be a mistake: "Different sites (and people) have different needs. No one syntax would make all happy."[19]

Gruber avoided using curly braces in Markdown to unofficially reserve them for implementation-specific extensions.[20]

Standardization
CommonMark
Filename extensions.md, .markdown[2]
Internet media typetext/markdown; variant=CommonMark[7]
Uniform Type Identifier (UTI)uncertain[21]
UTI conformationpublic.plain-text
Developed byJohn MacFarlane, open source
Initial releaseOctober 25, 2014 (2014-10-25)
Latest release
0.30
June 19, 2021 (2021-06-19)[22]
Type of formatOpen file format
Extended fromMarkdown
Extended toGitHub Flavored Markdown
Websitecommonmark.org spec.commonmark.org

From 2012, a group of people, including Jeff Atwood and John MacFarlane, launched what Atwood characterised as a standardisation effort.[11] A community website now aims to "document various tools and resources available to document authors and developers, as well as implementors of the various Markdown implementations".[23] In September 2014, Gruber objected to the usage of "Markdown" in the name of this effort and it was rebranded as CommonMark.[24][25] CommonMark.org published several versions of a specification, reference implementation, test suite, and "[plans] to announce a finalized 1.0 spec and test suite in 2019."[26] No 1.0 spec has since been released as major issues still remain unsolved.[27] Nonetheless, the following websites and projects have adopted CommonMark: Discourse, GitHub, GitLab, Reddit, Qt, Stack Exchange (Stack Overflow), and Swift.

In March 2016 two relevant informational Internet RFCs were published:

  • RFC 7763 introduced MIME type text/markdown.
  • RFC 7764 discussed and registered the variants MultiMarkdown, GitHub Flavored Markdown (GFM), Pandoc, and Markdown Extra among others.[28]

Variants

Websites like Bitbucket, Diaspora, GitHub,[29] OpenStreetMap, Reddit,[30] SourceForge,[31] and Stack Exchange[32] use variants of Markdown to make discussions between users easier.

Depending on implementation, basic inline HTML tags may be supported.[33] Italic text may be implemented by _underscores_ and/or *single-asterisks*.[34]

GitHub Flavored Markdown

GitHub had been using its own variant of Markdown since as early as 2009,[35] which added support for additional formatting such as tables and nesting block content inside list elements, as well as GitHub-specific features such as auto-linking references to commits, issues, usernames, etc. In 2017, GitHub released a formal specification of its GitHub Flavored Markdown (GFM) that is based on CommonMark.[29] It is a strict superset of CommonMark, following its specification exactly except for tables, strikethrough, autolinks and task lists, which GFM adds as extensions.[36] GitHub also changed the parser used on their sites accordingly, which required that some documents be changed. For instance, GFM now requires that the hash symbol that creates a heading be separated from the heading text by a space character.

Markdown Extra

Markdown Extra is a lightweight markup language based on Markdown implemented in PHP (originally), Python and Ruby.[37] It adds the following features that are not available with regular Markdown:

  • Markdown markup inside HTML blocks
  • Elements with id/class attribute
  • "Fenced code blocks" that span multiple lines of code
  • Tables[38]
  • Definition lists
  • Footnotes
  • Abbreviations

Markdown Extra is supported in some content management systems such as Drupal,[39] Grav (CMS) and TYPO3.[40]

LiaScript

LiaScript[41] is a Markdown dialect that was designed to create interactive educational content. It is implemented in Elm and TypeScript and adds additional syntax elements to define features like:

  • Animations
  • Automatic speech output
  • Mathematical formulas (using KaTeX)
  • ASCII art diagrams
  • Various types of quizzes and surveys
  • JavaScript is natively supported and can be attached to various elements, this way code fragments can be made executable and editable

Examples
Text using Markdown syntax Corresponding HTML produced by a Markdown processor Text viewed in a browser
Heading
=======

Sub-heading
-----------

# Alternative heading

## Alternative sub-heading

Paragraphs are separated 
by a blank line.

Two spaces at the end of a line  
produce a line break.

<h1>Heading</h1>

<h2>Sub-heading</h2>

<h1>Alternative heading</h1>

<h2>Alternative sub-heading</h2>

<p>Paragraphs are separated
by a blank line.</p>

<p>Two spaces at the end of a line<br />
produce a line break.</p>
Heading
Sub-heading
Alternative heading
Alternative sub-heading

Paragraphs are separated by a blank line.

Two spaces at the end of a line
produce a line break.

Text attributes _italic_, **bold**, `monospace`.

Horizontal rule:

---

<p>Text attributes <em>italic</em>, <strong>bold</strong>, <code>monospace</code>.</p>

<p>Horizontal rule:</p>

<hr />
Text attributes italic, bold, monospace.

Horizontal rule:

Bullet lists nested within numbered list:

  1. fruits
     * apple
     * banana
  2. vegetables
     - carrot
     - broccoli

<p>Bullet lists nested within numbered list:</p>

<ol>
  <li>fruits <ul>
      <li>apple</li>
      <li>banana</li>
  </ul></li>
  <li>vegetables <ul>
      <li>carrot</li>
      <li>broccoli</li>
  </ul></li>
</ol>
Bullet lists nested within numbered list:
  1. fruits
    • apple
    • banana
  2. vegetables
    • carrot
    • broccoli
A [link](http://example.com).

![Image](Icon-pictures.png "icon")

> Markdown uses email-style
characters for blockquoting.
>
> Multiple paragraphs need to be prepended individually.

Most inline <abbr title="Hypertext Markup Language">HTML</abbr> tags are supported.

<p>A <a href="http://example.com">link</a>.</p>

<p><img alt="Image" title="icon" src="Icon-pictures.png" /></p>

<blockquote>
<p>Markdown uses email-style characters for blockquoting.</p>
<p>Multiple paragraphs need to be prepended individually.</p>
</blockquote>

<p>Most inline <abbr title="Hypertext Markup Language">HTML</abbr> tags are supported.</p>
A link.

Image

Markdown uses email-style characters for blockquoting.

Multiple paragraphs need to be prepended individually.

Most inline HTML tags are supported.

Implementations

Implementations of Markdown are available for over a dozen programming languages; in addition, many applications, platforms and frameworks support Markdown.[42] For example, Markdown plugins exist for every major blogging platform.[43]

While Markdown is a minimal markup language and is read and edited with a normal text editor, there are specially designed editors that preview the files with styles, which are available for all major platforms. Many general-purpose text and code editors have syntax highlighting plugins for Markdown built into them or available as optional download. Editors may feature a side-by-side preview window or render the code directly in a WYSIWYG fashion.

Some apps, services and editors that support Markdown as an editing format, including:

See also

Explanatory notes
  1. Technically HTML description lists

References
  1. Gruber, John (8 January 2014). "The Markdown File Extension". The Daring Fireball Company, LLC. Archived from the original on 12 July 2020. Retrieved 27 March 2022. Too late now, I suppose, but the only file extension I would endorse is ".markdown", for the same reason offered by Hilton Lipschitz: We no longer live in a 8.3 world, so we should be using the most descriptive file extensions. It's sad that all our operating systems rely on this stupid convention instead of the better creator code or a metadata model, but great that they now support longer file extensions.
  2. Leonard, Sean (March 2016). "The text/markdown Media Type". Request for Comments: 7763. Internet Engineering Task Force. Archived from the original on 22 March 2022. Retrieved 27 March 2022. This document registers the text/markdown media type for use with Markdown, a family of plain-text formatting syntaxes that optionally can be converted to formal markup languages such as HTML.
  3. Swartz, Aaron (2004-03-19). "Markdown". Aaron Swartz: The Weblog. Archived from the original on 2017-12-24. Retrieved 2013-09-01.
  4. Gruber, John. "Markdown". Daring Fireball. Archived from the original on 2004-03-11. Retrieved 2022-08-20.
  5. Markdown 1.0.1 readme source code "Daring Fireball – Markdown". 2004-12-17. Archived from the original on 2004-04-02.
  6. "Markdown: License". Daring Fireball. Archived from the original on 2020-02-18. Retrieved 2014-04-25.
  7. Leonard, Sean (March 2016). "Guidance on Markdown: Design Philosophies, Stability Strategies, and Select Registrations". Request for Comments: 7764. Internet Engineering Task Force. Archived from the original on 17 April 2022. Retrieved 27 March 2022. This document elaborates upon the text/markdown media type for use with Markdown, a family of plain-text formatting syntaxes that optionally can be converted to formal markup languages such as HTML. Background information, local storage strategies, and additional syntax registrations are supplied.
  8. "RMarkdown Reference site". Archived from the original on 2020-03-03. Retrieved 2019-11-21.
  9. Markdown Syntax "Daring Fireball – Markdown – Syntax". 2013-06-13. "Readability, however, is emphasized above all else. A Markdown-formatted document should be publishable as-is, as plain text, without looking like it's been marked up with tags or formatting instructions. While Markdown's syntax has been influenced by several existing text-to-HTML filters — including Setext, atx, Textile, reStructuredText, Grutatext[12], and EtText[13] — the single biggest source of inspiration for Markdown's syntax is the format of plain text email."
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  19. Gruber, John [@gruber] (4 September 2014). "@tobie @espadrine @comex @wycats Because different sites (and people) have different needs. No one syntax would make all happy" (Tweet) – via Twitter.
  20. Gruber, John (19 May 2022). "Markdoc". Daring Fireball. Archived from the original on 19 May 2022. Retrieved May 19, 2022. I love their syntax extensions — very true to the spirit of Markdown. They use curly braces for their extensions; I'm not sure I ever made this clear, publicly, but I avoided using curly braces in Markdown itself — even though they are very tempting characters — to unofficially reserve them for implementation-specific extensions. Markdoc's extensive use of curly braces for its syntax is exactly the sort of thing I was thinking about.
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  26. "CommonMark". Archived from the original on 12 April 2016. Retrieved 20 Jun 2018. The current version of the CommonMark spec is complete, and quite robust after a year of public feedback … but not quite final. With your help, we plan to announce a finalized 1.0 spec and test suite in 2019.
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