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.
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
created the Markdown language in 2004 in collaboration with Aaron Swartz on the syntax, 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 ".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, unlike text formatted with a markup language, such as Rich Text Format 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.
Gruber wrote a Perl script,, 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.
Markdown has since been re-implemented by others e.g. in a Perl module available on CPAN, 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.
Sites like GitHub, Bitbucket, Reddit, Diaspora, Stack Exchange, OpenStreetMap, and SourceForge use variants of Markdown to facilitate discussion between users.
Standardization
Markdown has been characterised by an informal specification 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, 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. These issues spurred the creation of tools such as Babelmark to compare the output of various implementations, and an effort by some developers of Markdown parsers for standardisation. However, Gruber has argued that complete standardization would be mistaken: "Different sites have different needs. No one syntax would make all happy."In March 2016 two relevant informational Internet RFCs were published:
- RFC 7763 introduced MIME type with the original variant.
- RFC 7764 discussed and registered the variants MultiMarkdown, GitHub Flavored Markdown, Pandoc, CommonMark, and Markdown Extra among others.
CommonMark
GitHub Flavored Markdown (GFM)
In 2017, GitHub released a formal specification of their GitHub Flavored Markdown that is based on CommonMark. It is a strict superset of CommonMark, following its specification exactly except for tables, strikethrough, autolinks and task lists, which GFM adds as extensions. 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, Python and Ruby. It adds features not available with plain Markdown syntax. Markdown Extra is supported in some content management systems such as, for example, Drupal and TYPO3.In MediaWiki, it is implemented in the currently unmaintained 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
- definition lists
- footnotes
- abbreviations
Example
=
Sub-heading-----------
Paragraphs are separated
by a blank line.
Two spaces at the end of a line
produces a line break.
Heading
Sub-heading
Paragraphs are separated
by a blank line.
Two spaces at the end of a line
produces a line break.
font-size: 1.8em; font-family: Georgia,Times,serif; margin-top: 1em; margin-bottom: 0.25em; line-height: 1.3; padding: 0; border-bottom: 1px solid #AAAAAA;>Heading
!["Image"]("Icon-pictures.png" "\"icon\"")