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

Quick facts: Filename extensions, Internet media type...
Filename, .markdown[1][2]
Internet media typetext/markdown[2]
Uniform Type Identifier (UTI)net.daringfireball.markdown
Developed byJohn Gruber and Aaron Swartz
Initial releaseMarch 9, 2004 (18 years ago) (2004-03-09)[3][4]
Latest release
December 17, 2004 (17 years ago) (2004-12-17)[5]
Type of formatOpen file format[6]
Extended topandoc, MultiMarkdown, Markdown Extra, CommonMark,[7] RMarkdown[8]

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]