Markdown

Markdown is a lightweight markup language with plain-text-formatting syntax, created in 2004 by John Gruber with Aaron Swartz. Markdown is often used to format readme files, for writing messages in online discussion forums, and to create rich text using a plain text editor.

For the marketing term, see Price markdown.
Markdown
Internet media typetext/markdown[1]
Uniform Type Identifier (UTI)net.daringfireball.markdown
Developed byJohn Gruber (in collaboration with Aaron Swartz on the syntax)
Initial releaseMarch 19, 2004 (2004-03-19)[2][3]
Latest release
1.0.1
(December 17, 2004 (2004-12-17)[4])
Type of formatMarkup language
Extended toMultiMarkdown, Markdown Extra, CommonMark,[5] RMarkdown[6]
Open format?Yes[7]
Websitedaringfireball.net/projects/markdown/

Since the initial description of Markdown contained ambiguities and unanswered questions, the implementations that appeared over the years have subtle differences and many come with syntax extensions.

History

John Gruber created the Markdown language in 2004 in collaboration with Aaron Swartz on the syntax,[2][3] 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)".[4]

Its key design goal is readability – that the language be readable as-is, without looking like it has been marked up with tags or formatting instructions,[8] unlike text formatted with a markup language, such as Rich Text Format (RTF) or HTML, which have obvious tags and formatting instructions. To this end, its main inspiration is the existing conventions for marking up plain text in email, though it also draws from earlier markup languages, notably setext, Textile, and reStructuredText.[8]

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 be used as a standalone script, as a plugin for Blosxom or Movable Type, or as a text filter for BBEdit.[4]

Markdown has since been re-implemented by others e.g. in a Perl module available on CPAN (Text::Markdown), and in a variety of other programming languages.[9] It is distributed under a BSD-style license and is included with, or available as a plugin for, several content-management systems.[7][10][11]

Sites like GitHub, Bitbucket, Reddit, Diaspora, Stack Exchange, OpenStreetMap, and SourceForge use variants of Markdown to facilitate discussion between users.[12][13][14][15]

Standardization

Markdown has been characterised by an informal specification[16] and a reference implementation for conversion to HTML. Over time, many Markdown implementations have appeared. People developed these mostly driven by the need for additional features on top of the base syntax—such as tables, footnotes, definition lists (technically HTML description lists), and Markdown inside HTML blocks. The behavior of some of these diverges from the reference implementation. At the same time, a number of ambiguities in the informal specification have attracted attention.[17] These issues spurred the creation of tools such as Babelmark[18][19] to compare the output of various implementations,[20] and an effort by some developers of Markdown parsers for standardisation. However, Gruber has argued that complete standardization would be mistaken: "Different sites (and people) have different needs. No one syntax would make all happy."[21]

In March 2016 two relevant informational Internet RFCs were published:

CommonMark
CommonMark
Filename extensions.md, .markdown[1]
Internet media typetext/markdown; variant=CommonMark[5]
Uniform Type Identifier (UTI)uncertain[23]
UTI conformationpublic.plain-text
Developed byJohn MacFarlane, open source
Initial releaseOctober 25, 2014 (2014-10-25)
Latest release
0.29
(April 6, 2019 (2019-04-06)[24])
Type of formatMarkup language
Extended fromMarkdown
Extended toGitHub Flavored Markdown
Open format?yes
Websitespec.commonmark.org

From 2012, a group of people, including Jeff Atwood and John MacFarlane, launched what Atwood characterized as a standardization effort.[25] 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".[26] In September 2014, Gruber objected to the usage of "Markdown" in the name of this effort and it was rebranded as a new dialect named CommonMark.[27][28] CommonMark.org published several versions of a specification, reference implementation, and test suite, and "[plans] to announce a finalized 1.0 spec and test suite in 2019."[29]

GitHub Flavored Markdown (GFM)

In 2017, GitHub released a formal specification of their GitHub Flavored Markdown (GFM) that is based on CommonMark.[30] It is a strict superset of CommonMark, following its specification exactly except for tables, strikethrough, autolinks and task lists, which GFM adds as extensions.[31] 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.[32] It adds features not available with plain Markdown syntax. Markdown Extra is supported in some content management systems such as, for example, Drupal[33] and TYPO3.[34]

In MediaWiki, it is implemented in the currently unmaintained MarkdownExtraParser parser function extension

Markdown Extra adds the following features to Markdown:

  • markdown markup inside HTML blocks
  • elements with id/class attribute
  • "fenced code blocks" that span multiple lines of code
  • tables[35]
  • definition lists
  • footnotes
  • abbreviations

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

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

Paragraphs are separated
by a blank line.

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

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

Horizontal rule:

---

Strikethrough:
~~strikethrough~~

Bullet list:

  * apples
  * oranges
  * pears

Numbered list:

  1. lather
  2. rinse
  3. repeat

An [example](http://example.com).

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

> Markdown uses email-style > characters for blockquoting.

Inline <abbr title="Hypertext Markup Language">HTML</abbr> is supported.

<h1>Heading</h1>

<h2>Sub-heading</h2>

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

<p>Two spaces at the end of a line<br />
produces a line break.</p>

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

<p>Horizontal rule:</p>

<hr />

<p>Strikethrough:</p>
<strike>strikethrough</strike>

<p>Bullet list:</p>

<ul>
<li>apples</li>
<li>oranges</li>
<li>pears</li>
</ul>

<p>Numbered list:</p>

<ol>
<li>lather</li>
<li>rinse</li>
<li>repeat</li>
</ol>

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

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

<blockquote>
<p>Markdown uses email-style &gt; characters for blockquoting.</p>
</blockquote>

<p>Inline <abbr title="Hypertext Markup Language">HTML</abbr> is supported.</p>
Heading
Sub-heading

Paragraphs are separated by a blank line.

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

Text attributes italic, bold, monospace.

Horizontal rule:


Strikethrough:

strikethrough


Bullet list:

  • apples
  • oranges
  • pears

Numbered list:

  1. lather
  2. rinse
  3. repeat

An example.

Markdown uses email-style > characters for blockquoting.

Inline HTML is supported.

Implementations

Implementations of Markdown are available for over a dozen programming languages; in addition, many platforms and frameworks support Markdown.[36] For example, Markdown plugins exist for every major blogging platform.[37]

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.

  • Doxygen – a sourcecode documentation generator which supports Markdown with extra features.[38]
  • RStudio – an IDE for R. It provides a C++ wrapper function for a markdown variant called sundown.[39]
  • GitHub Flavored Markdown (GFM) ignores underscores in words, and adds syntax highlighting, task lists,[40] and tables.[41]
  • Discount – a C implementation.[42][43]
  • MarkAPL – a converter written in Dyalog APL. It supports fenced blocks, smart typography, link references, and special attributes, and can generate a table of contents.[44]
  • PHP Markdown – a library package that includes the PHP Markdown parser and its sibling PHP Markdown Extra with additional features.[45]
  • Markdig – a .NET library that follows the CommonMark specifications, and includes a collection of extensions and the ability for the user to create their own.

See also

References
  1. "RFC 7763 - The text/markdown Media Type".
  2. Swartz, Aaron (2004-03-19). "Markdown". Aaron Swartz: The Weblog.
  3. Gruber, John. "Markdown". Daring Fireball. Archived from the original on 2004-04-02. Retrieved 2014-04-25.
  4. Markdown 1.0.1 readme source code "Daring Fireball – Markdown". 2004-12-17. Archived from the original on 2004-04-02.
  5. "RFC7764 - Guidance on Markdown: Design Philosophies, Stability Strategies, and Select Registrations".
  6. "RMarkdown Reference site".
  7. "Markdown: License". Daring Fireball. Retrieved 2014-04-25.
  8. 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, and EtText — the single biggest source of inspiration for Markdown’s syntax is the format of plain text email.
  9. "Markdown 2.6.6". Python Software Foundation. 2016-03-21. Retrieved 2016-07-06.
  10. "MarsEdit 2.3 ties the knot with Tumblr support – Ars Technica". Retrieved 2009-08-11.
  11. "Review: Practical Django Projects – Ars Technica". Retrieved 2009-08-11.
  12. "GitHub Flavored Markdown". GitHub. Retrieved 2020-06-11.
  13. "Reddit markdown primer. Or, how do you do all that fancy formatting in your comments, anyway?". Reddit.com. Retrieved 2013-03-29.
  14. "Markdown Editing Help". StackOverflow.com. Retrieved 2014-04-11.
  15. "SourceForge: Markdown Syntax Guide". SourceForge.net. Retrieved 2013-05-10.
  16. "Markdown Syntax Documentation". Daring Fireball.
  17. "GitHub Flavored Markdown Spec". github.github.com.
  18. "Babelmark 2 - Compare markdown implementations". Johnmacfarlane.net. Retrieved 2014-04-25.
  19. "Babelmark 3 - Compare Markdown Implementations". github.io. Retrieved 2017-12-10.
  20. "Babelmark 2 - FAQ". Johnmacfarlane.net. Retrieved 2014-04-25.
  21. 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.
  22. "Markdown Variants". IANA. 2016-03-28. Retrieved 2016-07-06.
  23. "UTI of a CommonMark document".
  24. "CommonMark specification".
  25. Atwood, Jeff (2012-10-25). "The Future of Markdown". CodingHorror.com. Retrieved 2014-04-25.
  26. "Markdown Community Page". GitHub. Retrieved 2014-04-25.
  27. "Standard Markdown is now Common Markdown". Jeff Atwood. Retrieved 2014-10-07.
  28. "Standard Markdown Becomes Common Markdown then CommonMark". InfoQ. Retrieved 2014-10-07.
  29. "CommonMark". 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.
  30. "GitHub Flavored Markdown Spec".
  31. "A formal spec for GitHub Flavored Markdown". GitHub Engineering. Retrieved 16 Mar 2017.
  32. Fortin, Michel (2018). "PHP Markdown Extra". Michel Fortin website. Retrieved 2018-12-26.
  33. "Markdown editor for BUEditor". 4 December 2008.
  34. "Markdown for TYPO3 (markdown_content)". extensions.typo3.org.
  35. "PHP Markdown Extra". Michel Fortin.
  36. "W3C Community Page of Markdown Implementations". W3C Markdown Wiki. Retrieved 24 March 2016.
  37. "Markdown THrowdown – What happens when FOSS software gets corporate backing". Ars Technica. 2014-10-05.
  38. "Doxygen Manual: Markdown support".
  39. Allaire, J.J.; e.a. (2015-06-30). "Markdown.cpp". GitHub project RStudio. Retrieved 2016-07-07.
  40. "Writing on GitHub". help.github.com. GitHub, Inc. Retrieved 9 July 2014.
  41. "GitHub Flavored Markdown". github.com. Retrieved 11 June 2020.
  42. "Discount - a C implementation of the Markdown markup language". Retrieved 2020-03-01.
  43. Parsons, David (2016-05-28). "DISCOUNT". GitHub. Retrieved 2016-07-07. discount at Open Hub
  44. "Markdown converter written in Dyalog APL".
  45. "PHP Markdown". Retrieved 2016-03-01.
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