Markdown

Markdown is a lightweight markup language with plain text formatting syntax designed so that it can be converted to HTML and many other formats using a tool by the same name.^[6][7] 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.

History

John Gruber created the Markdown language in 2004, with significant collaboration from Aaron Swartz on the syntax,^[2][3] with the goal of enabling people "to write using an easy-to-read, easy-to-write plain text format, and optionally convert it to structurally valid XHTML (or HTML)”.^[4]

The 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, atx (by Aaron Swartz), Textile, reStructuredText, Grutatext, and EtText.^[8]

Gruber wrote a Perl script, Markdown.pl, which converts marked-up text input to valid, well-formed XHTML or HTML and replaces left-pointing 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 as a Perl module available on CPAN (Text::Markdown), and in a variety of other programming languages. It is distributed under a BSD-style license and is included with, or available as a plugin for, several content-management systems.^[5][9][10]

Sites such as GitHub, reddit, Diaspora, Stack Exchange, OpenStreetMap, and SourceForge use variants of Markdown to facilitate discussion between users.^{[11][12][13][14]} A Markdown dialect is also used by the instant messaging system Slack.^[15]

Standardization

There is no clearly defined Markdown standard, apart from the original writeup and implementation by John Gruber, which some consider abandonware.^[16][17] This has led to fragmentation as different vendors write their own variants of the language to correct flaws or add missing features.

From 2012 through 2014, a group of people including Jeff Atwood launched what Atwood characterized as a standardization effort.^[18] 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".^[19] 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.^[20][21]

A tool (named Babelmark2^[22]) is also available to "[compare] the output of various implementations" to "promote discussion of how and whether certain vague aspects of the markdown spec should be clarified".^[23] Gruber has argued that complete standardisation would be mistaken: "Different sites (and people) have different needs. No one syntax would make all happy."^[24]

A standards effort for the Internet media type text/markdown (independent of the syntax) is underway in the IETF. Plans are to submit the Internet-Draft, draft-ietf-appsawg-text-markdown to the IESG in April 2015. The Markdown community is invited to submit use cases for Markdown to inform the media type standardization process.

Extensions

A number of other lightweight markup languages extend Markdown by adding features (such as tables, footnotes, definition lists, and Markdown inside HTML blocks) not available in plain Markdown syntax. Among these are Markdown Extra, MultiMarkdown, and the Pandoc Markdown extension.^[25] In some cases, this is to enable conversion into more formats than just HTML, e.g., LaTeX, RTF, and DocBook.

Many implementations also intentionally omit support for middle word emphasis. The original Markdown implementation interprets constructs like my_long_variable as a request to emphasize "long" in the middle of a word. Many users found this confusing, so many later implementations such as PHP Markdown and Python Markdown do not implement middle word emphasis by default.^[26]

The essay "Thoughts on Markdown" stated that Markdown's original developer, John Gruber, has not responded to discussions about extensions to Markdown, and that "Markdown is changing, with or without him".^[27]

Example

Heading
=======

Sub-heading
-----------
 
### Another deeper heading
 
Paragraphs are separated
by a blank line.

Leave 2 spaces at the end of a line to do a  
line break

Text attributes *italic*, **bold**, 
`monospace`, ~~strikethrough~~ .

Shopping list:

  * apples
  * oranges
  * pears

Numbered list:

  1. apples
  2. oranges
  3. pears

The rain---not the reign---in
Spain.

A [link](http://example.com).

<h1>Heading</h1>

<h2>Sub-heading</h2>

<h3>Another deeper heading</h3>

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

<p>Leave 2 spaces at the end of a line to do a<br />
line break</p>

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

<p>Shopping list:</p>

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

<p>Numbered list:</p>

<ol>
<li>apples</li>
<li>oranges</li>
<li>pears</li>
</ol>

<p>The rain&mdash;not the
reign&mdash;in Spain.</p>

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

Editors

While Markdown is a minimal markup language and is easily read and edited with a normal text editor, there are specially designed editors that preview the files with styles. There are a variety of such editors available for all major platforms. There are syntax highlighting plugins for Markdown built into emacs, gedit, and vim. Atom has built-in side-by-side preview window.

Implementations

Implementations of Markdown are available for many different frameworks, platforms and languages.

• The sourcecode documentation generator Doxygen supports Markdown with extra features.^[29]
• RStudio, an IDE for R provides a C++ wrapper function for a markdown variant called sundown.^[30]
• IntelliJ IDEA, an IDE for Java, provides a Markdown plugin^[31][32]
• MultiMarkdown, a format and program with more syntax features and export options than traditional Markdown
• PageDown, a parser for StackExchange's Markdown syntax^[18]
• GitHub Flavored Markdown (GFM) treats newlines in paragraph-like content as real line breaks, ignores underscores in words, and adds syntax highlighting, task lists,^[33] and tables.^[11] It has several implementations:
  • "Grip - GitHub Readme Instant Preview" (Joe Esposito) - Python
  • "Vim-Flavored-Markdown" (Jeff Tratner) - Vim scripting
  • "GitHub-Flavored Markdown Comments" (Evan Solomon) - PHP WordPress plugin
  • "Markdown on Save" (Mark Jaquith) - PHP WordPress plugin
  • "Node-GFM" (Gabriel Llamas) - JavaScript
  • "Parsedown" (Emanuil Rusev) - PHP
• Pandoc adds tables, line blocks, definition lists, superscripts and subscripts, can generate table of contents.^[34]
• Discount - a C implementation.^[35]
• Md2doc - a XSLT 2.0 implementation.^[36]
• Visual Studio Web Essentials - an extension library for Microsoft Visual Studio with live markdown preview
• Markdown editing and live preview in Linux with a python module^[37]

Test suites

• Markdown Text Editor
• Markdown Test Suite

There are many more open-source implementations of Markdown available online.

See also

• Similar lightweight markup languages:
  • AsciiDoc, supports many document types
  • Org-mode
  • Textile
  • txt2tags
  • Wiki markup
• Comparison of document markup languages
• Comparison of documentation generators

References

External links

• Official website