Lightweight markup language

A lightweight markup language is a markup language with a simple syntax, designed to be easy for a human to enter with a simple text editor, and easy to read in its raw form.

Lightweight markup languages are used in applications where people might be expected to read the document source as well as the rendered output. For instance, a person downloading a software library might prefer to read the documentation in a text editor rather than a browser.

Another application is for entry in web-based publishing, such as weblogs and wikis, where the input interface is a simple text box. The server software converts the input to a common document markup language like HTML or XHTML.

History

Lightweight markup languages were originally used on text-only displays which could not display characters in italics or bold, so informal methods to convey this information had to be developed. This formatting choice was naturally carried forth to plain-text email communications.

1986 international standard SGML provided facilities to define and parse lightweight markup languages using grammars and tag implication. The 1998 W3C XML is a profile of SGML that omits these facilities.

Types

Presentation oriented languages include AsciiDoc, BBCode, Creole, Crossmark, deplate, Epytext, EtText, Haml, JsonML, MakeDoc, Markdown, Org-mode, POD, reStructuredText, Ruby Document format, Setext, SiSU, SPIP, Xupl, Texy!, Textile, txt2tags, UDO and Wikitext.

Data serialization oriented languages include Curl (programming language) (homoiconic, but also reads JSON; every object serializes), JSON, OGDL, Simple Declarative Language and YAML.

Comparison of language features

Comparing language features
Language	Implementation language or platf.	HTML export tool	HTML import tool	Tables	Link titles	class attribute	id attribute	Exportable formats	License
Asciidoc	Python	Yes	Yes	Yes	Yes	Yes	Yes	XHTML, LaTeX, PDF, DocBook, OpenDocument, EPUB, Man page, etc.	GNU GPL
BBCode	Perl, PHP, C#, Python, Ruby	No	No	No	No	No	No	HTML, XHTML	Public Domain
Creole	PHP, Python, Ruby, JavaScript ^[1]	No	No	Yes	No	No	No	Depends on impl.	CC-by-SA 1.0
deplate	Ruby	Yes	No	Yes	No	Yes	Yes	HTML, LaTeX, DocBook, plain text	GPL
Markdown	Perl (originally), C,^[2]^[3] Python, JavaScript, Haskell,^[4] Ruby,^[5] C#, Java, PHP. Features are implementation dependent.	Yes	Yes	Yes	Yes	Yes	Yes	HTML originally; depending on the implementation, also LaTeX, ConTeXt, RTF, PDF, OpenDocument, DocBook, EPUB, MediaWiki, ReStructuredText, Man page, S5 (file format), etc.	BSD-style & GPL (both)
Markdown Extra	PHP (originally), Python, Ruby	Yes	Yes	Yes^[6]	Yes	No	No	XHTML	BSD-style & GPL (both)
MediaWiki	Perl, PHP	Yes	Yes	Yes	Yes	Yes	Yes	XHTML	GNU GPL
Org-mode	Emacs Lisp, Ruby (parser only), Perl	Yes	?	Yes	Yes	?	?	Plain text, HTML, LaTeX, PDF, DocBook, TaskJuggler, Freemind, XOXO, iCalendar	GPL
PmWiki	PHP	No	Yes	Yes	Yes	Yes	Yes	XHTML 1.0 Transitional	GNU GPL
POD	Perl	Yes	?	No	Yes	?	?	HTML, XHTML, XML, Man page, LaTeX, plain text, RTF, DocBook	Artistic License, Perl's license
reStructuredText	Python, Haskell, Java,	Yes	No	Yes	Yes	Yes	auto	LaTeX, XML, Man page, HTML (w3c valid), PDF, S5 (file format), ODF	Public Domain
Textile	PHP, Java, Perl, Python, Ruby, ASP, C#	Yes	No	Yes	Yes	Yes	Yes	XHTML	Textile License
Texy!	PHP, C#; Java in progress	Yes	Yes	Yes	Yes	Yes	Yes	XHTML or HTML	GNU GPL v2 License
Txt2tags	Python	Yes	?	Yes^[7]	Yes	?	?	HTML, XHTML, SGML, Creole, Asciidoc, MediaWiki/Wikipedia, MoinMoin, PmWiki, DokuWiki, Google Code Wiki, LaTeX, roff, Man page, MagicPoint, Lout, PageMaker, ASCII Art and Plain-text	GPL

Comparison of lightweight markup language syntax

Text/font-face formatting

Comparing text formatting syntax
Language	Bold	Italic	Monospace (teletype)	Notes
AsciiDoc	`bold text`	`_italic text_`	`+monospace text+`	Can double operators to ignore special characters (for example `bold _text` yields bold _text).
BBCode	`[b]bold text[/b]`	`[i]italic text[/i]`	`[code]monospace text[/code]`	Formatting works across line breaks.
Creole	`bold text`	`//italic text//`	`{{{monospace text}}}`	Triple curly braces are for nowiki which is optionally monospace in Creole (the choice of the implementor). Future Creole additions may introduce double hash marks (##) for monospace.
deplate	`{text style=bold: bold text}`	`__emphasized text__`	`''monospace text''`	deplate discourages visual formatting. Users who want to format text in a particular style have to define style classes in the given output format (CSS, LaTeX). By default, emphasized text is formatted in italics.
Markdown^[8]	`bold text` or `__bold text__`	`italic text` or `_italic text_`	`Non-monospace text` `monospace text` `more monospace text` Inline `monospaced` text.	Markdown doesn't use bold and italic tags, but rather `em` (typically italic) and `strong` (typically bold) tags. Monospace text is created by indenting that line 4 spaces or one tab character, or enclosing text in backticks: `monospaces`.
MediaWiki	`'''bold text'''`	`''italic text''`	`<code>monospace text</code>`
Org-mode	`bold text`	`/italic text/`	`=code= or ~verbatim~`	`_underlined_ +strike-through+`
PmWiki	`'''bold text'''`	`''italic text''`	`@@monospace text@@`
POD	`B<bold text>`	`I<italic text>`	`C<monospace text>`	Indented text is also shown as monospaced code.
reStructuredText	`bold text`	`italic text`	``monospace text``
Setext	`bold text`	`~italic text~`
Textile^[9]	`bold text` or `bold text`	`_italic text_` or `__italic text__`	`@monospace text@`	Textile uses `em` (typically italic) and `strong` (typically bold) tags on single symbols (and `code` tag), and `i` and `b` tags on double symbols.
Texy!	`bold text`	`italic text` or `//italic text//`	`monospace text`	Texy uses by default `em` (typically italic) and `strong` (typically bold) tags. It is possible to configure library to use another tags.
txt2tags	`bold text`	`//italic text//`	``monospace text``	`__underlined__ --strike-through--`

Section headers

Comparing section header formatting
Language	Format	Notes
AsciiDoc	`= Level 1 Header` `== Level 2 Header ==` `=== Level 3 Header` or Level 1 Header ============== Level 2 Header -------------- Level 3 Header ~~~~~~~~~~~~~~	Close equals signs are optional (ignored if present). Level 1 is document/page title.
BBCode		Does not support section headers
Creole	`= Level 1 Header` `== Level 2 Header ==` `=== Level 3 Header`	Close equals signs are optional (ignored if present).
deplate	`* Level 1 Header` ` Level 2 Header` `* Level 3 Header`	deplate's default markup is historically based on EmacsWiki, which in turn is the base for Org-mode.
Markdown^[8]	`# Level 1 Header` `## Level 2 Header` or Level 1 Header ============== Level 2 Header --------------	You can optionally "close" the #-style headers with an equal number of #'s. The #-style headers support up to 6 levels. The = and - style headers support only the two shown.
MediaWiki	`== Level 2 Header ==` `=== Level 3 Header ===`	= is available for level 1 header, but its use is discouraged in Wikipedia (reserved for page title). More = are possible, up to 6.
Org-mode	Default: * Level 1 Header Level 2 Header * Level 3 Header	Cleaner view using `org-indent-view` * Level 1 Header * Level 2 Header * Level 3 Header
PmWiki	`!! Level 2 Header` `!!! Level 3 Header`	! is available for level 1 header, but its use is discouraged in PmWiki (used for the page title). More ! are possible, up to 6.
POD	`=head1 Level 1 heading` `=head2 Level 2 heading`
reStructuredText	Chapter 1 Title =============== Section 1.1 Title ----------------- Subsection 1.1.1 Title ~~~~~~~~~~~~~~~~~~~~~~ Section 1.2 Title ----------------- Chapter 2 Title ===============	Any of the following characters can be used as the "underline": = - ` : ' " ~ ^ _ * + # < >. The same character must be used for the same indentation level and may not be used for a new indentation level.
Textile^[9]	`h1. Level 1 Header` `h2. Level 2 Header`	Up to 6 levels
Texy!	`### Level 1 Header` `## Level 2 Header` or Level 1 Header ============== Level 2 Header --------------	You can optionally "close" the #-style headers with an equal number of #'s. The #-style headers support up to 6 levels. The underlined style headers support four levels (### *** === ----). Resulting absolute levels numbers are calculated dynamically. Optionally, less chars can denote higher header level.
txt2tags	`= Level 1 Header =` `== Level 2 Header ==` `=== Level 3 Header ===`	Up to 6 levels. Using `+` characters instead of `=` characters creates numbered headers (the default being unnumbered).

Link syntax

Comparing link syntax
Language	Syntax	Notes
AsciiDoc	`http://www.example.com` `http://www.example.com[Link text]`
BBCode	`[url]http://www.example.com[/url]` `[url=http://www.example.com]Link text[/url]`	Some BBCode implementations can auto-parse URLs as well and convert them to `a` elements.
Creole	`[[Internal Page]]` `[[Internal Page\|Display Text]]` `[[http://www.example.com\|Link text]]` `[[WikiCreole:Creole1.0\|InterWiki Link]]`	Free standing URL's are also detected.
deplate	`[[Internal Page]]` `[[Internal Page][Display Text]]` `[[http://www.example.com][Link text]]` `[[WikiCreole::Creole1.0][InterWiki Link]]`	Free standing URL's are also detected. The format is close to Org-mode -- see below.
Markdown^[8]	`<http://www.example.com>` or `[Link text](http://www.example.com "optional title attribute")` or `[Link text][id]` and elsewhere `[id]: http://www.example.com "optional title attribute"`	Allows for an optional `title` attribute.
MediaWiki	`[[Internal page]]` `[[Internal page\|Displayed text]]` `[http://www.example.com]` `[http://www.example.com External link]`	Wikitext can auto-parse URLs as well and convert them to `a` elements.
Org-mode	link format: `[[link][description]] or [[link]]` `[[My Target][Find my target]]` - text search in current file `[[#my-custom-id]]` - link to custom id `[[http://orgmode.org]]` - external link `[[http://orgmode.org][Org Mode]] - external link with description` `[[file:/path/to/some/file]] or [[/path/to/some/file]] or [[./some/file]]` - file system links
PmWiki	`[[Internal page]]` `[[Internal page\|Displayed text]]` `[[http://www.pmwiki.org]]` `[[http://www.Pmwiki.org\|External link]]`	Wikitext can auto-parse URLs without spaces in them as well and convert them to `a` elements.
POD	`L</Internal Link>` `L<Perl::Module::Link>` `L<http://example.com/external_link>`	The core POD standard does not support external links with titles.
reStructuredText	`Link text <http://www.example.com/>`_ or `Linkname_` and elsewhere `.. _Linkname: http://example.com`
Textile^[9]	`"Link text (optional title attribute)":http://www.example.com` or `"Link text":alias` and elsewhere `[alias (optional title attribute)]http://www.example.com`	Allows for an optional `title` attribute.
Texy!	`"Link text .(optional title)[opt. class or ID]{opt. style}":http://www.example.com` or `"Link text":alias` and elsewhere `[alias]: http://www.example.com .(optional title)[opt. class or ID]{opt. style}`	Texy! modifiers allows for an optional `title` attribute, CSS classes, ID, inline style and HTML element attributes. Example: "Link .(title)[class#id]{color: blue;rel:nofollow}"
txt2tags	`[Link text www.example.com]`	Txt2tags can auto-parse URLs as well and convert them to `a` elements. Also has support for targeting references within the same text, not just URLs.

References

^ WikiCreole: Converters
^ peg-markdown is an implementation of markdown in C.
^ Discount is also an implementation of markdown in C.
^ Pandoc, which is written in Haskell, parses Markdown (in two forms) and ReStructuredText, as well as HTML and LaTeX; it writes from any of these formats to HTML, RTF, LaTeX, ConTeXt, OpenDocument, EPUB and several other formats, including (via LaTeX) PDF.
^ https://rubyforge.org/projects/kramdown/
^ PHP Markdown Extra
^ Txt2tags User Guide
^ ^a ^b ^c Markdown Syntax
^ ^a ^b ^c Textile Syntax

External links

[1] WikiCreole: Converters

[2] -markdown is an implementation of markdown in C.

[3] Discount is also an implementation of markdown in C.

[4] Pandoc, which is written in Haskell, parses Markdown (in two forms) and ReStructuredText, as well as HTML and LaTeX; it writes from any of these formats to HTML, RTF, LaTeX, ConTeXt, OpenDocument, EPUB and several other formats, including (via LaTeX) PDF.

[5] ttps://rubyforge.org/projects/kramdown/

[6] PHP Markdown Extra

[7] Txt2tags User Guide

[markdown_syntax-8] Markdown Syntax

[textile_syntax-9] Textile Syntax

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