From Wikipedia, the free encyclopedia en.wikipedia.org/wiki/Markdown
Markdown is a plain text formatting syntax designed so that it optionally can be converted to HTML using a tool by the same name. Markdown is popularly used to format readme files, for writing messages in online discussion forums or in text editors for the quick creation of rich text documents.
The Markdown language was created in 2004 by John Gruber with substantial contributions from Aaron Swartz, with the goal of allowing people “to write using an easy-to-read, easy-to-write plain text format, and optionally convert it to structurally valid XHTML (or HTML)”.
Taking cues from existing conventions for marking up plain text in email such as setext, the language was designed to be readable as-is, without looking like it’s been marked up with tags or formatting instructions, unlike text formatted with a Markup language, such as HTML, which has obvious tags and formatting instructions. Markdown is a formatting syntax for text that can be read by humans and can be easily converted to HTML.
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.
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.
Sites such as GitHub, reddit, Diaspora, Stack Exchange, OpenStreetMap, and SourceForge use variants of Markdown to facilitate discussion between users.
There is no clearly defined Markdown standard, apart from the original writeup and implementation by John Gruber, which is considered to be abandonware, leading to fragmentation as different vendors write their own variants of the language to correct flaws or add missing features.