---
title: CommonMark Spec
author: John MacFarlane
-version: 0.26
-date: '2016-07-15'
+version: 0.27
+date: '2016-11-18'
license: '[CC-BY-SA 4.0](http://creativecommons.org/licenses/by-sa/4.0/)'
...
## What is Markdown?
Markdown is a plain text format for writing structured documents,
-based on conventions used for indicating formatting in email and
-usenet posts. It was developed in 2004 by John Gruber, who wrote
-the first Markdown-to-HTML converter in Perl, and it soon became
-ubiquitous. In the next decade, dozens of implementations were
+based on conventions for indicating formatting in email
+and usenet posts. It was developed by John Gruber (with
+help from Aaron Swartz) and released in 2004 in the form of a
+[syntax description](http://daringfireball.net/projects/markdown/syntax)
+and a Perl script (`Markdown.pl`) for converting Markdown to
+HTML. In the next decade, dozens of implementations were
developed in many languages. Some extended the original
Markdown syntax with conventions for footnotes, tables, and
other document elements. Some allowed Markdown documents to be
characters].
A [Unicode whitespace character](@) is
-any code point in the Unicode `Zs` class, or a tab (`U+0009`),
+any code point in the Unicode `Zs` general category, or a tab (`U+0009`),
carriage return (`U+000D`), newline (`U+000A`), or form feed
(`U+000C`).
A [punctuation character](@) is an [ASCII
punctuation character] or anything in
-the Unicode classes `Pc`, `Pd`, `Pe`, `Pf`, `Pi`, `Po`, or `Ps`.
+the general Unicode categories `Pc`, `Pd`, `Pe`, `Pf`, `Pi`, `Po`, or `Ps`.
## Tabs
Normally the `>` that begins a block quote may be followed
optionally by a space, which is not considered part of the
content. In the following case `>` is followed by a tab,
-which is treated as if it were expanded into spaces.
-Since one of theses spaces is considered part of the
+which is treated as if it were expanded into three spaces.
+Since one of these spaces is considered part of the
delimiter, `foo` is considered to be indented six spaces
inside the block quote context, so we get an indented
code block starting with two spaces.
quotations, lists, headings, rules, and code blocks. Some blocks (like
block quotes and list items) contain other blocks; others (like
headings and paragraphs) contain [inline](@) content---text,
-links, emphasized text, images, code, and so on.
+links, emphasized text, images, code spans, and so on.
## Precedence
<p>`foo</p>
````````````````````````````````
+The following case also illustrates the need for opening and
+closing backtick strings to be equal in length:
+
+```````````````````````````````` example
+`foo``bar``
+.
+<p>`foo<code>bar</code></p>
+````````````````````````````````
+
## Emphasis and strong emphasis
A [left-flanking delimiter run](@) is
a [delimiter run] that is (a) not followed by [Unicode whitespace],
-and (b) either not followed by a [punctuation character], or
+and (b) not followed by a [punctuation character], or
preceded by [Unicode whitespace] or a [punctuation character].
For purposes of this definition, the beginning and the end of
the line count as Unicode whitespace.
A [right-flanking delimiter run](@) is
a [delimiter run] that is (a) not preceded by [Unicode whitespace],
-and (b) either not preceded by a [punctuation character], or
+and (b) not preceded by a [punctuation character], or
followed by [Unicode whitespace] or a [punctuation character].
For purposes of this definition, the beginning and the end of
the line count as Unicode whitespace.
7. A double `**` [can close strong emphasis](@)
iff it is part of a [right-flanking delimiter run].
-8. A double `__` [can close strong emphasis]
+8. A double `__` [can close strong emphasis] iff
it is part of a [right-flanking delimiter run]
and either (a) not part of a [left-flanking delimiter run]
or (b) part of a [left-flanking delimiter run]
an interpretation `<strong>...</strong>` is always preferred to
`<em><em>...</em></em>`.
-14. An interpretation `<strong><em>...</em></strong>` is always
- preferred to `<em><strong>..</strong></em>`.
+14. An interpretation `<em><strong>...</strong></em>` is always
+ preferred to `<strong><em>...</em></strong>`.
15. When two potential emphasis or strong emphasis spans overlap,
so that the second begins before the first ends and ends after
```````````````````````````````` example
***foo***
.
-<p><strong><em>foo</em></strong></p>
+<p><em><strong>foo</strong></em></p>
````````````````````````````````
```````````````````````````````` example
_____foo_____
.
-<p><strong><strong><em>foo</em></strong></strong></p>
+<p><em><strong><strong>foo</strong></strong></em></p>
````````````````````````````````
- a nonempty sequence of characters that does not include
ASCII space or control characters, and includes parentheses
only if (a) they are backslash-escaped or (b) they are part of
- a balanced pair of unescaped parentheses that is not itself
- inside a balanced pair of unescaped parentheses.
+ a balanced pair of unescaped parentheses.
A [link title](@) consists of either
<p><a href="(foo)">link</a></p>
````````````````````````````````
-One level of balanced parentheses is allowed without escaping:
-
-```````````````````````````````` example
-[link]((foo)and(bar))
-.
-<p><a href="(foo)and(bar)">link</a></p>
-````````````````````````````````
-
-However, if you have parentheses within parentheses, you need to escape
-or use the `<...>` form:
+Any number parentheses are allowed without escaping, as long as they are
+balanced:
```````````````````````````````` example
[link](foo(and(bar)))
.
-<p>[link](foo(and(bar)))</p>
+<p><a href="foo(and(bar))">link</a></p>
````````````````````````````````
+However, if you have unbalanced parentheses, you need to escape or use the
+`<...>` form:
```````````````````````````````` example
-[link](foo(and\(bar\)))
+[link](foo\(and\(bar\))
.
-<p><a href="foo(and(bar))">link</a></p>
+<p><a href="foo(and(bar)">link</a></p>
````````````````````````````````
```````````````````````````````` example
-[link](<foo(and(bar))>)
+[link](<foo(and(bar)>)
.
-<p><a href="foo(and(bar))">link</a></p>
+<p><a href="foo(and(bar)">link</a></p>
````````````````````````````````
````````````````````````````````
-If you just want bracketed text, you can backslash-escape the
-opening `!` and `[`:
+If you just want a literal `!` followed by bracketed text, you can
+backslash-escape the opening `[`:
```````````````````````````````` example
-\!\[foo]
+!\[foo]
[foo]: /url "title"
.
Code Review / simantics / platform.git / commitdiff