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---
title: CommonMark Spec
author: John MacFarlane
version: 0.27
date: '2016-11-18'
license: '[CC-BY-SA 4.0](http://creativecommons.org/licenses/by-sa/4.0/)'
...
# Introduction
## 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
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
rendered in formats other than HTML. Websites like Reddit,
StackOverflow, and GitHub had millions of people using Markdown.
And Markdown started to be used beyond the web, to author books,
articles, slide shows, letters, and lecture notes.
What distinguishes Markdown from many other lightweight markup
syntaxes, which are often easier to write, is its readability.
As Gruber writes:
> The overriding design goal for Markdown's formatting syntax is
> to make it as readable as possible. The idea is that a
> Markdown-formatted document should be publishable as-is, as
> plain text, without looking like it's been marked up with tags
> or formatting instructions.
> (<http://daringfireball.net/projects/markdown/>)
The point can be illustrated by comparing a sample of
[AsciiDoc](http://www.methods.co.nz/asciidoc/) with
an equivalent sample of Markdown. Here is a sample of
AsciiDoc from the AsciiDoc manual:
```
1. List item one.
+
List item one continued with a second paragraph followed by an
Indented block.
+
.................
$ ls *.sh
$ mv *.sh ~/tmp
.................
+
List item continued with a third paragraph.
2. List item two continued with an open block.
+
--
This paragraph is part of the preceding list item.
a. This list is nested and does not require explicit item
continuation.
+
This paragraph is part of the preceding list item.
b. List item b.
This paragraph belongs to item two of the outer list.
--
```
And here is the equivalent in Markdown:
```
1. List item one.
List item one continued with a second paragraph followed by an
Indented block.
$ ls *.sh
$ mv *.sh ~/tmp
List item continued with a third paragraph.
2. List item two continued with an open block.
This paragraph is part of the preceding list item.
1. This list is nested and does not require explicit item continuation.
This paragraph is part of the preceding list item.
2. List item b.
This paragraph belongs to item two of the outer list.
```
The AsciiDoc version is, arguably, easier to write. You don't need
to worry about indentation. But the Markdown version is much easier
to read. The nesting of list items is apparent to the eye in the
source, not just in the processed document.
## Why is a spec needed?
John Gruber's [canonical description of Markdown's
syntax](http://daringfireball.net/projects/markdown/syntax)
does not specify the syntax unambiguously. Here are some examples of
questions it does not answer:
1. How much indentation is needed for a sublist? The spec says that
continuation paragraphs need to be indented four spaces, but is
not fully explicit about sublists. It is natural to think that
they, too, must be indented four spaces, but `Markdown.pl` does
not require that. This is hardly a "corner case," and divergences
between implementations on this issue often lead to surprises for
users in real documents. (See [this comment by John
Gruber](http://article.gmane.org/gmane.text.markdown.general/1997).)
2. Is a blank line needed before a block quote or heading?
Most implementations do not require the blank line. However,
this can lead to unexpected results in hard-wrapped text, and
also to ambiguities in parsing (note that some implementations
put the heading inside the blockquote, while others do not).
(John Gruber has also spoken [in favor of requiring the blank
lines](http://article.gmane.org/gmane.text.markdown.general/2146).)
3. Is a blank line needed before an indented code block?
(`Markdown.pl` requires it, but this is not mentioned in the
documentation, and some implementations do not require it.)
``` markdown
paragraph
code?
```
4. What is the exact rule for determining when list items get
wrapped in `<p>` tags? Can a list be partially "loose" and partially
"tight"? What should we do with a list like this?
``` markdown
1. one
2. two
3. three
```
Or this?
``` markdown
1. one
- a
- b
2. two
```
(There are some relevant comments by John Gruber
[here](http://article.gmane.org/gmane.text.markdown.general/2554).)
5. Can list markers be indented? Can ordered list markers be right-aligned?
``` markdown
8. item 1
9. item 2
10. item 2a
```
6. Is this one list with a thematic break in its second item,
or two lists separated by a thematic break?
``` markdown
* a
* * * * *
* b
```
7. When list markers change from numbers to bullets, do we have
two lists or one? (The Markdown syntax description suggests two,
but the perl scripts and many other implementations produce one.)
``` markdown
1. fee
2. fie
- foe
- fum
```
8. What are the precedence rules for the markers of inline structure?
For example, is the following a valid link, or does the code span
take precedence ?
``` markdown
[a backtick (`)](/url) and [another backtick (`)](/url).
```
9. What are the precedence rules for markers of emphasis and strong
emphasis? For example, how should the following be parsed?
``` markdown
*foo *bar* baz*
```
10. What are the precedence rules between block-level and inline-level
structure? For example, how should the following be parsed?
``` markdown
- `a long code span can contain a hyphen like this
- and it can screw things up`
```
11. Can list items include section headings? (`Markdown.pl` does not
allow this, but does allow blockquotes to include headings.)
``` markdown
- # Heading
```
12. Can list items be empty?
``` markdown
* a
*
* b
```
13. Can link references be defined inside block quotes or list items?
``` markdown
> Blockquote [foo].
>
> [foo]: /url
```
14. If there are multiple definitions for the same reference, which takes
precedence?
``` markdown
[foo]: /url1
[foo]: /url2
[foo][]
```
In the absence of a spec, early implementers consulted `Markdown.pl`
to resolve these ambiguities. But `Markdown.pl` was quite buggy, and
gave manifestly bad results in many cases, so it was not a
satisfactory replacement for a spec.
Because there is no unambiguous spec, implementations have diverged
considerably. As a result, users are often surprised to find that
a document that renders one way on one system (say, a github wiki)
renders differently on another (say, converting to docbook using
pandoc). To make matters worse, because nothing in Markdown counts
as a "syntax error," the divergence often isn't discovered right away.
## About this document
This document attempts to specify Markdown syntax unambiguously.
It contains many examples with side-by-side Markdown and
HTML. These are intended to double as conformance tests. An
accompanying script `spec_tests.py` can be used to run the tests
against any Markdown program:
python test/spec_tests.py --spec spec.txt --program PROGRAM
Since this document describes how Markdown is to be parsed into
an abstract syntax tree, it would have made sense to use an abstract
representation of the syntax tree instead of HTML. But HTML is capable
of representing the structural distinctions we need to make, and the
choice of HTML for the tests makes it possible to run the tests against
an implementation without writing an abstract syntax tree renderer.
This document is generated from a text file, `spec.txt`, written
in Markdown with a small extension for the side-by-side tests.
The script `tools/makespec.py` can be used to convert `spec.txt` into
HTML or CommonMark (which can then be converted into other formats).
In the examples, the `→` character is used to represent tabs.
# Preliminaries
## Characters and lines
Any sequence of [characters] is a valid CommonMark
document.
A [character](@) is a Unicode code point. Although some
code points (for example, combining accents) do not correspond to
characters in an intuitive sense, all code points count as characters
for purposes of this spec.
This spec does not specify an encoding; it thinks of lines as composed
of [characters] rather than bytes. A conforming parser may be limited
to a certain encoding.
A [line](@) is a sequence of zero or more [characters]
other than newline (`U+000A`) or carriage return (`U+000D`),
followed by a [line ending] or by the end of file.
A [line ending](@) is a newline (`U+000A`), a carriage return
(`U+000D`) not followed by a newline, or a carriage return and a
following newline.
A line containing no characters, or a line containing only spaces
(`U+0020`) or tabs (`U+0009`), is called a [blank line](@).
The following definitions of character classes will be used in this spec:
A [whitespace character](@) is a space
(`U+0020`), tab (`U+0009`), newline (`U+000A`), line tabulation (`U+000B`),
form feed (`U+000C`), or carriage return (`U+000D`).
[Whitespace](@) is a sequence of one or more [whitespace
characters].
A [Unicode whitespace character](@) is
any code point in the Unicode `Zs` class, or a tab (`U+0009`),
carriage return (`U+000D`), newline (`U+000A`), or form feed
(`U+000C`).
[Unicode whitespace](@) is a sequence of one
or more [Unicode whitespace characters].
A [space](@) is `U+0020`.
A [non-whitespace character](@) is any character
that is not a [whitespace character].
An [ASCII punctuation character](@)
is `!`, `"`, `#`, `$`, `%`, `&`, `'`, `(`, `)`,
`*`, `+`, `,`, `-`, `.`, `/`, `:`, `;`, `<`, `=`, `>`, `?`, `@`,
`[`, `\`, `]`, `^`, `_`, `` ` ``, `{`, `|`, `}`, or `~`.
A [punctuation character](@) is an [ASCII
punctuation character] or anything in
the Unicode classes `Pc`, `Pd`, `Pe`, `Pf`, `Pi`, `Po`, or `Ps`.
## Tabs
Tabs in lines are not expanded to [spaces]. However,
in contexts where whitespace helps to define block structure,
tabs behave as if they were replaced by spaces with a tab stop
of 4 characters.
Thus, for example, a tab can be used instead of four spaces
in an indented code block. (Note, however, that internal
tabs are passed through as literal tabs, not expanded to
spaces.)
```````````````````````````````` example
→foo→baz→→bim
.
<pre><code>foo→baz→→bim
</code></pre>
````````````````````````````````
```````````````````````````````` example
→foo→baz→→bim
.
<pre><code>foo→baz→→bim
</code></pre>
````````````````````````````````
```````````````````````````````` example
a→a
ὐ→a
.
<pre><code>a→a
ὐ→a
</code></pre>
````````````````````````````````
In the following example, a continuation paragraph of a list
item is indented with a tab; this has exactly the same effect
as indentation with four spaces would:
```````````````````````````````` example
- foo
→bar
.
<ul>
<li>
<p>foo</p>
<p>bar</p>
</li>
</ul>
````````````````````````````````
```````````````````````````````` example
- foo
→→bar
.
<ul>
<li>
<p>foo</p>
<pre><code> bar
</code></pre>
</li>
</ul>
````````````````````````````````
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
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.
```````````````````````````````` example
>→→foo
.
<blockquote>
<pre><code> foo
</code></pre>
</blockquote>
````````````````````````````````
```````````````````````````````` example
-→→foo
.
<ul>
<li>
<pre><code> foo
</code></pre>
</li>
</ul>
````````````````````````````````
```````````````````````````````` example
foo
→bar
.
<pre><code>foo
bar
</code></pre>
````````````````````````````````
```````````````````````````````` example
- foo
- bar
→ - baz
.
<ul>
<li>foo
<ul>
<li>bar
<ul>
<li>baz</li>
</ul>
</li>
</ul>
</li>
</ul>
````````````````````````````````
```````````````````````````````` example
#→Foo
.
<h1>Foo</h1>
````````````````````````````````
```````````````````````````````` example
*→*→*→
.
<hr />
````````````````````````````````
## Insecure characters
For security reasons, the Unicode character `U+0000` must be replaced
with the REPLACEMENT CHARACTER (`U+FFFD`).
# Blocks and inlines
We can think of a document as a sequence of
[blocks](@)---structural elements like paragraphs, block
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.
## Precedence
Indicators of block structure always take precedence over indicators
of inline structure. So, for example, the following is a list with
two items, not a list with one item containing a code span:
```````````````````````````````` example
- `one
- two`
.
<ul>
<li>`one</li>
<li>two`</li>
</ul>
````````````````````````````````
This means that parsing can proceed in two steps: first, the block
structure of the document can be discerned; second, text lines inside
paragraphs, headings, and other block constructs can be parsed for inline
structure. The second step requires information about link reference
definitions that will be available only at the end of the first
step. Note that the first step requires processing lines in sequence,
but the second can be parallelized, since the inline parsing of
one block element does not affect the inline parsing of any other.
## Container blocks and leaf blocks
We can divide blocks into two types:
[container block](@)s,
which can contain other blocks, and [leaf block](@)s,
which cannot.
# Leaf blocks
This section describes the different kinds of leaf block that make up a
Markdown document.
## Thematic breaks
A line consisting of 0-3 spaces of indentation, followed by a sequence
of three or more matching `-`, `_`, or `*` characters, each followed
optionally by any number of spaces, forms a
[thematic break](@).
```````````````````````````````` example
***
---
___
.
<hr />
<hr />
<hr />
````````````````````````````````
Wrong characters:
```````````````````````````````` example
+++
.
<p>+++</p>
````````````````````````````````
```````````````````````````````` example
===
.
<p>===</p>
````````````````````````````````
Not enough characters:
```````````````````````````````` example
--
**
__
.
<p>--
**
__</p>
````````````````````````````````
One to three spaces indent are allowed:
```````````````````````````````` example
***
***
***
.
<hr />
<hr />
<hr />
````````````````````````````````
Four spaces is too many:
```````````````````````````````` example
***
.
<pre><code>***
</code></pre>
````````````````````````````````
```````````````````````````````` example
Foo
***
.
<p>Foo
***</p>
````````````````````````````````
More than three characters may be used:
```````````````````````````````` example
_____________________________________
.
<hr />
````````````````````````````````
Spaces are allowed between the characters:
```````````````````````````````` example
- - -
.
<hr />
````````````````````````````````
```````````````````````````````` example
** * ** * ** * **
.
<hr />
````````````````````````````````
```````````````````````````````` example
- - - -
.
<hr />
````````````````````````````````
Spaces are allowed at the end:
```````````````````````````````` example
- - - -
.
<hr />
````````````````````````````````
However, no other characters may occur in the line:
```````````````````````````````` example
_ _ _ _ a
a------
---a---
.
<p>_ _ _ _ a</p>
<p>a------</p>
<p>---a---</p>
````````````````````````````````
It is required that all of the [non-whitespace characters] be the same.
So, this is not a thematic break:
```````````````````````````````` example
*-*
.
<p><em>-</em></p>
````````````````````````````````
Thematic breaks do not need blank lines before or after:
```````````````````````````````` example
- foo
***
- bar
.
<ul>
<li>foo</li>
</ul>
<hr />
<ul>
<li>bar</li>
</ul>
````````````````````````````````
Thematic breaks can interrupt a paragraph:
```````````````````````````````` example
Foo
***
bar
.
<p>Foo</p>
<hr />
<p>bar</p>
````````````````````````````````
If a line of dashes that meets the above conditions for being a
thematic break could also be interpreted as the underline of a [setext
heading], the interpretation as a
[setext heading] takes precedence. Thus, for example,
this is a setext heading, not a paragraph followed by a thematic break:
```````````````````````````````` example
Foo
---
bar
.
<h2>Foo</h2>
<p>bar</p>
````````````````````````````````
When both a thematic break and a list item are possible
interpretations of a line, the thematic break takes precedence:
```````````````````````````````` example
* Foo
* * *
* Bar
.
<ul>
<li>Foo</li>
</ul>
<hr />
<ul>
<li>Bar</li>
</ul>
````````````````````````````````
If you want a thematic break in a list item, use a different bullet:
```````````````````````````````` example
- Foo
- * * *
.
<ul>
<li>Foo</li>
<li>
<hr />
</li>
</ul>
````````````````````````````````
## ATX headings
An [ATX heading](@)
consists of a string of characters, parsed as inline content, between an
opening sequence of 1--6 unescaped `#` characters and an optional
closing sequence of any number of unescaped `#` characters.
The opening sequence of `#` characters must be followed by a
[space] or by the end of line. The optional closing sequence of `#`s must be
preceded by a [space] and may be followed by spaces only. The opening
`#` character may be indented 0-3 spaces. The raw contents of the
heading are stripped of leading and trailing spaces before being parsed
as inline content. The heading level is equal to the number of `#`
characters in the opening sequence.
Simple headings:
```````````````````````````````` example
# foo
## foo
### foo
#### foo
##### foo
###### foo
.
<h1>foo</h1>
<h2>foo</h2>
<h3>foo</h3>
<h4>foo</h4>
<h5>foo</h5>
<h6>foo</h6>
````````````````````````````````
More than six `#` characters is not a heading:
```````````````````````````````` example
####### foo
.
<p>####### foo</p>
````````````````````````````````
At least one space is required between the `#` characters and the
heading's contents, unless the heading is empty. Note that many
implementations currently do not require the space. However, the
space was required by the
[original ATX implementation](http://www.aaronsw.com/2002/atx/atx.py),
and it helps prevent things like the following from being parsed as
headings:
```````````````````````````````` example
#5 bolt
#hashtag
.
<p>#5 bolt</p>
<p>#hashtag</p>
````````````````````````````````
This is not a heading, because the first `#` is escaped:
```````````````````````````````` example
\## foo
.
<p>## foo</p>
````````````````````````````````
Contents are parsed as inlines:
```````````````````````````````` example
# foo *bar* \*baz\*
.
<h1>foo <em>bar</em> *baz*</h1>
````````````````````````````````
Leading and trailing blanks are ignored in parsing inline content:
```````````````````````````````` example
# foo
.
<h1>foo</h1>
````````````````````````````````
One to three spaces indentation are allowed:
```````````````````````````````` example
### foo
## foo
# foo
.
<h3>foo</h3>
<h2>foo</h2>
<h1>foo</h1>
````````````````````````````````
Four spaces are too much:
```````````````````````````````` example
# foo
.
<pre><code># foo
</code></pre>
````````````````````````````````
```````````````````````````````` example
foo
# bar
.
<p>foo
# bar</p>
````````````````````````````````
A closing sequence of `#` characters is optional:
```````````````````````````````` example
## foo ##
### bar ###
.
<h2>foo</h2>
<h3>bar</h3>
````````````````````````````````
It need not be the same length as the opening sequence:
```````````````````````````````` example
# foo ##################################
##### foo ##
.
<h1>foo</h1>
<h5>foo</h5>
````````````````````````````````
Spaces are allowed after the closing sequence:
```````````````````````````````` example
### foo ###
.
<h3>foo</h3>
````````````````````````````````
A sequence of `#` characters with anything but [spaces] following it
is not a closing sequence, but counts as part of the contents of the
heading:
```````````````````````````````` example
### foo ### b
.
<h3>foo ### b</h3>
````````````````````````````````
The closing sequence must be preceded by a space:
```````````````````````````````` example
# foo#
.
<h1>foo#</h1>
````````````````````````````````
Backslash-escaped `#` characters do not count as part
of the closing sequence:
```````````````````````````````` example
### foo \###
## foo #\##
# foo \#
.
<h3>foo ###</h3>
<h2>foo ###</h2>
<h1>foo #</h1>
````````````````````````````````
ATX headings need not be separated from surrounding content by blank
lines, and they can interrupt paragraphs:
```````````````````````````````` example
****
## foo
****
.
<hr />
<h2>foo</h2>
<hr />
````````````````````````````````
```````````````````````````````` example
Foo bar
# baz
Bar foo
.
<p>Foo bar</p>
<h1>baz</h1>
<p>Bar foo</p>
````````````````````````````````
ATX headings can be empty:
```````````````````````````````` example
##
#
### ###
.
<h2></h2>
<h1></h1>
<h3></h3>
````````````````````````````````
## Setext headings
A [setext heading](@) consists of one or more
lines of text, each containing at least one [non-whitespace
character], with no more than 3 spaces indentation, followed by
a [setext heading underline]. The lines of text must be such
that, were they not followed by the setext heading underline,
they would be interpreted as a paragraph: they cannot be
interpretable as a [code fence], [ATX heading][ATX headings],
[block quote][block quotes], [thematic break][thematic breaks],
[list item][list items], or [HTML block][HTML blocks].
A [setext heading underline](@) is a sequence of
`=` characters or a sequence of `-` characters, with no more than 3
spaces indentation and any number of trailing spaces. If a line
containing a single `-` can be interpreted as an
empty [list items], it should be interpreted this way
and not as a [setext heading underline].
The heading is a level 1 heading if `=` characters are used in
the [setext heading underline], and a level 2 heading if `-`
characters are used. The contents of the heading are the result
of parsing the preceding lines of text as CommonMark inline
content.
In general, a setext heading need not be preceded or followed by a
blank line. However, it cannot interrupt a paragraph, so when a
setext heading comes after a paragraph, a blank line is needed between
them.
Simple examples:
```````````````````````````````` example
Foo *bar*
=========
Foo *bar*
---------
.
<h1>Foo <em>bar</em></h1>
<h2>Foo <em>bar</em></h2>
````````````````````````````````
The content of the header may span more than one line:
```````````````````````````````` example
Foo *bar
baz*
====
.
<h1>Foo <em>bar
baz</em></h1>
````````````````````````````````
The underlining can be any length:
```````````````````````````````` example
Foo
-------------------------
Foo
=
.
<h2>Foo</h2>
<h1>Foo</h1>
````````````````````````````````
The heading content can be indented up to three spaces, and need
not line up with the underlining:
```````````````````````````````` example
Foo
---
Foo
-----
Foo
===
.
<h2>Foo</h2>
<h2>Foo</h2>
<h1>Foo</h1>
````````````````````````````````
Four spaces indent is too much:
```````````````````````````````` example
Foo
---
Foo
---
.
<pre><code>Foo
---
Foo
</code></pre>
<hr />
````````````````````````````````
The setext heading underline can be indented up to three spaces, and
may have trailing spaces:
```````````````````````````````` example
Foo
----
.
<h2>Foo</h2>
````````````````````````````````
Four spaces is too much:
```````````````````````````````` example
Foo
---
.
<p>Foo
---</p>
````````````````````````````````
The setext heading underline cannot contain internal spaces:
```````````````````````````````` example
Foo
= =
Foo
--- -
.
<p>Foo
= =</p>
<p>Foo</p>
<hr />
````````````````````````````````
Trailing spaces in the content line do not cause a line break:
```````````````````````````````` example
Foo
-----
.
<h2>Foo</h2>
````````````````````````````````
Nor does a backslash at the end:
```````````````````````````````` example
Foo\
----
.
<h2>Foo\</h2>
````````````````````````````````
Since indicators of block structure take precedence over
indicators of inline structure, the following are setext headings:
```````````````````````````````` example
`Foo
----
`
<a title="a lot
---
of dashes"/>
.
<h2>`Foo</h2>
<p>`</p>
<h2>&lt;a title=&quot;a lot</h2>
<p>of dashes&quot;/&gt;</p>
````````````````````````````````
The setext heading underline cannot be a [lazy continuation
line] in a list item or block quote:
```````````````````````````````` example
> Foo
---
.
<blockquote>
<p>Foo</p>
</blockquote>
<hr />
````````````````````````````````
```````````````````````````````` example
> foo
bar
===
.
<blockquote>
<p>foo
bar
===</p>
</blockquote>
````````````````````````````````
```````````````````````````````` example
- Foo
---
.
<ul>
<li>Foo</li>
</ul>
<hr />
````````````````````````````````
A blank line is needed between a paragraph and a following
setext heading, since otherwise the paragraph becomes part
of the heading's content:
```````````````````````````````` example
Foo
Bar
---
.
<h2>Foo
Bar</h2>
````````````````````````````````
But in general a blank line is not required before or after
setext headings:
```````````````````````````````` example
---
Foo
---
Bar
---
Baz
.
<hr />
<h2>Foo</h2>
<h2>Bar</h2>
<p>Baz</p>
````````````````````````````````
Setext headings cannot be empty:
```````````````````````````````` example
====
.
<p>====</p>
````````````````````````````````
Setext heading text lines must not be interpretable as block
constructs other than paragraphs. So, the line of dashes
in these examples gets interpreted as a thematic break:
```````````````````````````````` example
---
---
.
<hr />
<hr />
````````````````````````````````
```````````````````````````````` example
- foo
-----
.
<ul>
<li>foo</li>
</ul>
<hr />
````````````````````````````````
```````````````````````````````` example
foo
---
.
<pre><code>foo
</code></pre>
<hr />
````````````````````````````````
```````````````````````````````` example
> foo
-----
.
<blockquote>
<p>foo</p>
</blockquote>
<hr />
````````````````````````````````
If you want a heading with `> foo` as its literal text, you can
use backslash escapes:
```````````````````````````````` example
\> foo
------
.
<h2>&gt; foo</h2>
````````````````````````````````
**Compatibility note:** Most existing Markdown implementations
do not allow the text of setext headings to span multiple lines.
But there is no consensus about how to interpret
``` markdown
Foo
bar
---
baz
```
One can find four different interpretations:
1. paragraph "Foo", heading "bar", paragraph "baz"
2. paragraph "Foo bar", thematic break, paragraph "baz"
3. paragraph "Foo bar --- baz"
4. heading "Foo bar", paragraph "baz"
We find interpretation 4 most natural, and interpretation 4
increases the expressive power of CommonMark, by allowing
multiline headings. Authors who want interpretation 1 can
put a blank line after the first paragraph:
```````````````````````````````` example
Foo
bar
---
baz
.
<p>Foo</p>
<h2>bar</h2>
<p>baz</p>
````````````````````````````````
Authors who want interpretation 2 can put blank lines around
the thematic break,
```````````````````````````````` example
Foo
bar
---
baz
.
<p>Foo
bar</p>
<hr />
<p>baz</p>
````````````````````````````````
or use a thematic break that cannot count as a [setext heading
underline], such as
```````````````````````````````` example
Foo
bar
* * *
baz
.
<p>Foo
bar</p>
<hr />
<p>baz</p>
````````````````````````````````
Authors who want interpretation 3 can use backslash escapes:
```````````````````````````````` example
Foo
bar
\---
baz
.
<p>Foo
bar
---
baz</p>
````````````````````````````````
## Indented code blocks
An [indented code block](@) is composed of one or more
[indented chunks] separated by blank lines.
An [indented chunk](@) is a sequence of non-blank lines,
each indented four or more spaces. The contents of the code block are
the literal contents of the lines, including trailing
[line endings], minus four spaces of indentation.
An indented code block has no [info string].
An indented code block cannot interrupt a paragraph, so there must be
a blank line between a paragraph and a following indented code block.
(A blank line is not needed, however, between a code block and a following
paragraph.)
```````````````````````````````` example
a simple
indented code block
.
<pre><code>a simple
indented code block
</code></pre>
````````````````````````````````
If there is any ambiguity between an interpretation of indentation
as a code block and as indicating that material belongs to a [list
item][list items], the list item interpretation takes precedence:
```````````````````````````````` example
- foo
bar
.
<ul>
<li>
<p>foo</p>
<p>bar</p>
</li>
</ul>
````````````````````````````````
```````````````````````````````` example
1. foo
- bar
.
<ol>
<li>
<p>foo</p>
<ul>
<li>bar</li>
</ul>
</li>
</ol>
````````````````````````````````
The contents of a code block are literal text, and do not get parsed
as Markdown:
```````````````````````````````` example
<a/>
*hi*
- one
.
<pre><code>&lt;a/&gt;
*hi*
- one
</code></pre>
````````````````````````````````
Here we have three chunks separated by blank lines:
```````````````````````````````` example
chunk1
chunk2
chunk3
.
<pre><code>chunk1
chunk2
chunk3
</code></pre>
````````````````````````````````
Any initial spaces beyond four will be included in the content, even
in interior blank lines:
```````````````````````````````` example
chunk1
chunk2
.
<pre><code>chunk1
chunk2
</code></pre>
````````````````````````````````
An indented code block cannot interrupt a paragraph. (This
allows hanging indents and the like.)
```````````````````````````````` example
Foo
bar
.
<p>Foo
bar</p>
````````````````````````````````
However, any non-blank line with fewer than four leading spaces ends
the code block immediately. So a paragraph may occur immediately
after indented code:
```````````````````````````````` example
foo
bar
.
<pre><code>foo
</code></pre>
<p>bar</p>
````````````````````````````````
And indented code can occur immediately before and after other kinds of
blocks:
```````````````````````````````` example
# Heading
foo
Heading
------
foo
----
.
<h1>Heading</h1>
<pre><code>foo
</code></pre>
<h2>Heading</h2>
<pre><code>foo
</code></pre>
<hr />
````````````````````````````````
The first line can be indented more than four spaces:
```````````````````````````````` example
foo
bar
.
<pre><code> foo
bar
</code></pre>
````````````````````````````````
Blank lines preceding or following an indented code block
are not included in it:
```````````````````````````````` example
foo
.
<pre><code>foo
</code></pre>
````````````````````````````````
Trailing spaces are included in the code block's content:
```````````````````````````````` example
foo
.
<pre><code>foo
</code></pre>
````````````````````````````````
## Fenced code blocks
A [code fence](@) is a sequence
of at least three consecutive backtick characters (`` ` ``) or
tildes (`~`). (Tildes and backticks cannot be mixed.)
A [fenced code block](@)
begins with a code fence, indented no more than three spaces.
The line with the opening code fence may optionally contain some text
following the code fence; this is trimmed of leading and trailing
spaces and called the [info string](@).
The [info string] may not contain any backtick
characters. (The reason for this restriction is that otherwise
some inline code would be incorrectly interpreted as the
beginning of a fenced code block.)
The content of the code block consists of all subsequent lines, until
a closing [code fence] of the same type as the code block
began with (backticks or tildes), and with at least as many backticks
or tildes as the opening code fence. If the leading code fence is
indented N spaces, then up to N spaces of indentation are removed from
each line of the content (if present). (If a content line is not
indented, it is preserved unchanged. If it is indented less than N
spaces, all of the indentation is removed.)
The closing code fence may be indented up to three spaces, and may be
followed only by spaces, which are ignored. If the end of the
containing block (or document) is reached and no closing code fence
has been found, the code block contains all of the lines after the
opening code fence until the end of the containing block (or
document). (An alternative spec would require backtracking in the
event that a closing code fence is not found. But this makes parsing
much less efficient, and there seems to be no real down side to the
behavior described here.)
A fenced code block may interrupt a paragraph, and does not require
a blank line either before or after.
The content of a code fence is treated as literal text, not parsed
as inlines. The first word of the [info string] is typically used to
specify the language of the code sample, and rendered in the `class`
attribute of the `code` tag. However, this spec does not mandate any
particular treatment of the [info string].
Here is a simple example with backticks:
```````````````````````````````` example
```
<
>
```
.
<pre><code>&lt;
&gt;
</code></pre>
````````````````````````````````
With tildes:
```````````````````````````````` example
~~~
<
>
~~~
.
<pre><code>&lt;
&gt;
</code></pre>
````````````````````````````````
The closing code fence must use the same character as the opening
fence:
```````````````````````````````` example
```
aaa
~~~
```
.
<pre><code>aaa
~~~
</code></pre>
````````````````````````````````
```````````````````````````````` example
~~~
aaa
```
~~~
.
<pre><code>aaa
```
</code></pre>
````````````````````````````````
The closing code fence must be at least as long as the opening fence:
```````````````````````````````` example
````
aaa
```
``````
.
<pre><code>aaa
```
</code></pre>
````````````````````````````````
```````````````````````````````` example
~~~~
aaa
~~~
~~~~
.
<pre><code>aaa
~~~
</code></pre>
````````````````````````````````
Unclosed code blocks are closed by the end of the document
(or the enclosing [block quote][block quotes] or [list item][list items]):
```````````````````````````````` example
```
.
<pre><code></code></pre>
````````````````````````````````
```````````````````````````````` example
`````
```
aaa
.
<pre><code>
```
aaa
</code></pre>
````````````````````````````````
```````````````````````````````` example
> ```
> aaa
bbb
.
<blockquote>
<pre><code>aaa
</code></pre>
</blockquote>
<p>bbb</p>
````````````````````````````````
A code block can have all empty lines as its content:
```````````````````````````````` example
```
```
.
<pre><code>
</code></pre>
````````````````````````````````
A code block can be empty:
```````````````````````````````` example
```
```
.
<pre><code></code></pre>
````````````````````````````````
Fences can be indented. If the opening fence is indented,
content lines will have equivalent opening indentation removed,
if present:
```````````````````````````````` example
```
aaa
aaa
```
.
<pre><code>aaa
aaa
</code></pre>
````````````````````````````````
```````````````````````````````` example
```
aaa
aaa
aaa
```
.
<pre><code>aaa
aaa
aaa
</code></pre>
````````````````````````````````
```````````````````````````````` example
```
aaa
aaa
aaa
```
.
<pre><code>aaa
aaa
aaa
</code></pre>
````````````````````````````````
Four spaces indentation produces an indented code block:
```````````````````````````````` example
```
aaa
```
.
<pre><code>```
aaa
```
</code></pre>
````````````````````````````````
Closing fences may be indented by 0-3 spaces, and their indentation
need not match that of the opening fence:
```````````````````````````````` example
```
aaa
```
.
<pre><code>aaa
</code></pre>
````````````````````````````````
```````````````````````````````` example
```
aaa
```
.
<pre><code>aaa
</code></pre>
````````````````````````````````
This is not a closing fence, because it is indented 4 spaces:
```````````````````````````````` example
```
aaa
```
.
<pre><code>aaa
```
</code></pre>
````````````````````````````````
Code fences (opening and closing) cannot contain internal spaces:
```````````````````````````````` example
``` ```
aaa
.
<p><code></code>
aaa</p>
````````````````````````````````
```````````````````````````````` example
~~~~~~
aaa
~~~ ~~
.
<pre><code>aaa
~~~ ~~
</code></pre>
````````````````````````````````
Fenced code blocks can interrupt paragraphs, and can be followed
directly by paragraphs, without a blank line between:
```````````````````````````````` example
foo
```
bar
```
baz
.
<p>foo</p>
<pre><code>bar
</code></pre>
<p>baz</p>
````````````````````````````````
Other blocks can also occur before and after fenced code blocks
without an intervening blank line:
```````````````````````````````` example
foo
---
~~~
bar
~~~
# baz
.
<h2>foo</h2>
<pre><code>bar
</code></pre>
<h1>baz</h1>
````````````````````````````````
An [info string] can be provided after the opening code fence.
Opening and closing spaces will be stripped, and the first word, prefixed
with `language-`, is used as the value for the `class` attribute of the
`code` element within the enclosing `pre` element.
```````````````````````````````` example
```ruby
def foo(x)
return 3
end
```
.
<pre><code class="language-ruby">def foo(x)
return 3
end
</code></pre>
````````````````````````````````
```````````````````````````````` example
~~~~ ruby startline=3 $%@#$
def foo(x)
return 3
end
~~~~~~~
.
<pre><code class="language-ruby">def foo(x)
return 3
end
</code></pre>
````````````````````````````````
```````````````````````````````` example
````;
````
.
<pre><code class="language-;"></code></pre>
````````````````````````````````
[Info strings] for backtick code blocks cannot contain backticks:
```````````````````````````````` example
``` aa ```
foo
.
<p><code>aa</code>
foo</p>
````````````````````````````````
Closing code fences cannot have [info strings]:
```````````````````````````````` example
```
``` aaa
```
.
<pre><code>``` aaa
</code></pre>
````````````````````````````````
## HTML blocks
An [HTML block](@) is a group of lines that is treated
as raw HTML (and will not be escaped in HTML output).
There are seven kinds of [HTML block], which can be defined
by their start and end conditions. The block begins with a line that
meets a [start condition](@) (after up to three spaces
optional indentation). It ends with the first subsequent line that
meets a matching [end condition](@), or the last line of
the document or other [container block]), if no line is encountered that meets the
[end condition]. If the first line meets both the [start condition]
and the [end condition], the block will contain just that line.
1. **Start condition:** line begins with the string `<script`,
`<pre`, or `<style` (case-insensitive), followed by whitespace,
the string `>`, or the end of the line.\
**End condition:** line contains an end tag
`</script>`, `</pre>`, or `</style>` (case-insensitive; it
need not match the start tag).
2. **Start condition:** line begins with the string `<!--`.\
**End condition:** line contains the string `-->`.
3. **Start condition:** line begins with the string `<?`.\
**End condition:** line contains the string `?>`.
4. **Start condition:** line begins with the string `<!`
followed by an uppercase ASCII letter.\
**End condition:** line contains the character `>`.
5. **Start condition:** line begins with the string
`<![CDATA[`.\
**End condition:** line contains the string `]]>`.
6. **Start condition:** line begins the string `<` or `</`
followed by one of the strings (case-insensitive) `address`,
`article`, `aside`, `base`, `basefont`, `blockquote`, `body`,
`caption`, `center`, `col`, `colgroup`, `dd`, `details`, `dialog`,
`dir`, `div`, `dl`, `dt`, `fieldset`, `figcaption`, `figure`,
`footer`, `form`, `frame`, `frameset`,
`h1`, `h2`, `h3`, `h4`, `h5`, `h6`, `head`, `header`, `hr`,
`html`, `iframe`, `legend`, `li`, `link`, `main`, `menu`, `menuitem`,
`meta`, `nav`, `noframes`, `ol`, `optgroup`, `option`, `p`, `param`,
`section`, `source`, `summary`, `table`, `tbody`, `td`,
`tfoot`, `th`, `thead`, `title`, `tr`, `track`, `ul`, followed
by [whitespace], the end of the line, the string `>`, or
the string `/>`.\
**End condition:** line is followed by a [blank line].
7. **Start condition:** line begins with a complete [open tag]
or [closing tag] (with any [tag name] other than `script`,
`style`, or `pre`) followed only by [whitespace]
or the end of the line.\
**End condition:** line is followed by a [blank line].
All types of [HTML blocks] except type 7 may interrupt
a paragraph. Blocks of type 7 may not interrupt a paragraph.
(This restriction is intended to prevent unwanted interpretation
of long tags inside a wrapped paragraph as starting HTML blocks.)
Some simple examples follow. Here are some basic HTML blocks
of type 6:
```````````````````````````````` example
<table>
<tr>
<td>
hi
</td>
</tr>
</table>
okay.
.
<table>
<tr>
<td>
hi
</td>
</tr>
</table>
<p>okay.</p>
````````````````````````````````
```````````````````````````````` example
<div>
*hello*
<foo><a>
.
<div>
*hello*
<foo><a>
````````````````````````````````
A block can also start with a closing tag:
```````````````````````````````` example
</div>
*foo*
.
</div>
*foo*
````````````````````````````````
Here we have two HTML blocks with a Markdown paragraph between them:
```````````````````````````````` example
<DIV CLASS="foo">
*Markdown*
</DIV>
.
<DIV CLASS="foo">
<p><em>Markdown</em></p>
</DIV>
````````````````````````````````
The tag on the first line can be partial, as long
as it is split where there would be whitespace:
```````````````````````````````` example
<div id="foo"
class="bar">
</div>
.
<div id="foo"
class="bar">
</div>
````````````````````````````````
```````````````````````````````` example
<div id="foo" class="bar
baz">
</div>
.
<div id="foo" class="bar
baz">
</div>
````````````````````````````````
An open tag need not be closed:
```````````````````````````````` example
<div>
*foo*
*bar*
.
<div>
*foo*
<p><em>bar</em></p>
````````````````````````````````
A partial tag need not even be completed (garbage
in, garbage out):
```````````````````````````````` example
<div id="foo"
*hi*
.
<div id="foo"
*hi*
````````````````````````````````
```````````````````````````````` example
<div class
foo
.
<div class
foo
````````````````````````````````
The initial tag doesn't even need to be a valid
tag, as long as it starts like one:
```````````````````````````````` example
<div *???-&&&-<---
*foo*
.
<div *???-&&&-<---
*foo*
````````````````````````````````
In type 6 blocks, the initial tag need not be on a line by
itself:
```````````````````````````````` example
<div><a href="bar">*foo*</a></div>
.
<div><a href="bar">*foo*</a></div>
````````````````````````````````
```````````````````````````````` example
<table><tr><td>
foo
</td></tr></table>
.
<table><tr><td>
foo
</td></tr></table>
````````````````````````````````
Everything until the next blank line or end of document
gets included in the HTML block. So, in the following
example, what looks like a Markdown code block
is actually part of the HTML block, which continues until a blank
line or the end of the document is reached:
```````````````````````````````` example
<div></div>
``` c
int x = 33;
```
.
<div></div>
``` c
int x = 33;
```
````````````````````````````````
To start an [HTML block] with a tag that is *not* in the
list of block-level tags in (6), you must put the tag by
itself on the first line (and it must be complete):
```````````````````````````````` example
<a href="foo">
*bar*
</a>
.
<a href="foo">
*bar*
</a>
````````````````````````````````
In type 7 blocks, the [tag name] can be anything:
```````````````````````````````` example
<Warning>
*bar*
</Warning>
.
<Warning>
*bar*
</Warning>
````````````````````````````````
```````````````````````````````` example
<i class="foo">
*bar*
</i>
.
<i class="foo">
*bar*
</i>
````````````````````````````````
```````````````````````````````` example
</ins>
*bar*
.
</ins>
*bar*
````````````````````````````````
These rules are designed to allow us to work with tags that
can function as either block-level or inline-level tags.
The `<del>` tag is a nice example. We can surround content with
`<del>` tags in three different ways. In this case, we get a raw
HTML block, because the `<del>` tag is on a line by itself:
```````````````````````````````` example
<del>
*foo*
</del>
.
<del>
*foo*
</del>
````````````````````````````````
In this case, we get a raw HTML block that just includes
the `<del>` tag (because it ends with the following blank
line). So the contents get interpreted as CommonMark:
```````````````````````````````` example
<del>
*foo*
</del>
.
<del>
<p><em>foo</em></p>
</del>
````````````````````````````````
Finally, in this case, the `<del>` tags are interpreted
as [raw HTML] *inside* the CommonMark paragraph. (Because
the tag is not on a line by itself, we get inline HTML
rather than an [HTML block].)
```````````````````````````````` example
<del>*foo*</del>
.
<p><del><em>foo</em></del></p>
````````````````````````````````
HTML tags designed to contain literal content
(`script`, `style`, `pre`), comments, processing instructions,
and declarations are treated somewhat differently.
Instead of ending at the first blank line, these blocks
end at the first line containing a corresponding end tag.
As a result, these blocks can contain blank lines:
A pre tag (type 1):
```````````````````````````````` example
<pre language="haskell"><code>
import Text.HTML.TagSoup
main :: IO ()
main = print $ parseTags tags
</code></pre>
okay
.
<pre language="haskell"><code>
import Text.HTML.TagSoup
main :: IO ()
main = print $ parseTags tags
</code></pre>
<p>okay</p>
````````````````````````````````
A script tag (type 1):
```````````````````````````````` example
<script type="text/javascript">
// JavaScript example
document.getElementById("demo").innerHTML = "Hello JavaScript!";
</script>
okay
.
<script type="text/javascript">
// JavaScript example
document.getElementById("demo").innerHTML = "Hello JavaScript!";
</script>
<p>okay</p>
````````````````````````````````
A style tag (type 1):
```````````````````````````````` example
<style
type="text/css">
h1 {color:red;}
p {color:blue;}
</style>
okay
.
<style
type="text/css">
h1 {color:red;}
p {color:blue;}
</style>
<p>okay</p>
````````````````````````````````
If there is no matching end tag, the block will end at the
end of the document (or the enclosing [block quote][block quotes]
or [list item][list items]):
```````````````````````````````` example
<style
type="text/css">
foo
.
<style
type="text/css">
foo
````````````````````````````````
```````````````````````````````` example
> <div>
> foo
bar
.
<blockquote>
<div>
foo
</blockquote>
<p>bar</p>
````````````````````````````````
```````````````````````````````` example
- <div>
- foo
.
<ul>
<li>
<div>
</li>
<li>foo</li>
</ul>
````````````````````````````````
The end tag can occur on the same line as the start tag:
```````````````````````````````` example
<style>p{color:red;}</style>
*foo*
.
<style>p{color:red;}</style>
<p><em>foo</em></p>
````````````````````````````````
```````````````````````````````` example
<!-- foo -->*bar*
*baz*
.
<!-- foo -->*bar*
<p><em>baz</em></p>
````````````````````````````````
Note that anything on the last line after the
end tag will be included in the [HTML block]:
```````````````````````````````` example
<script>
foo
</script>1. *bar*
.
<script>
foo
</script>1. *bar*
````````````````````````````````
A comment (type 2):
```````````````````````````````` example
<!-- Foo
bar
baz -->
okay
.
<!-- Foo
bar
baz -->
<p>okay</p>
````````````````````````````````
A processing instruction (type 3):
```````````````````````````````` example
<?php
echo '>';
?>
okay
.
<?php
echo '>';
?>
<p>okay</p>
````````````````````````````````
A declaration (type 4):
```````````````````````````````` example
<!DOCTYPE html>
.
<!DOCTYPE html>
````````````````````````````````
CDATA (type 5):
```````````````````````````````` example
<![CDATA[
function matchwo(a,b)
{
if (a < b && a < 0) then {
return 1;
} else {
return 0;
}
}
]]>
okay
.
<![CDATA[
function matchwo(a,b)
{
if (a < b && a < 0) then {
return 1;
} else {
return 0;
}
}
]]>
<p>okay</p>
````````````````````````````````
The opening tag can be indented 1-3 spaces, but not 4:
```````````````````````````````` example
<!-- foo -->
<!-- foo -->
.
<!-- foo -->
<pre><code>&lt;!-- foo --&gt;
</code></pre>
````````````````````````````````
```````````````````````````````` example
<div>
<div>
.
<div>
<pre><code>&lt;div&gt;
</code></pre>
````````````````````````````````
An HTML block of types 1--6 can interrupt a paragraph, and need not be
preceded by a blank line.
```````````````````````````````` example
Foo
<div>
bar
</div>
.
<p>Foo</p>
<div>
bar
</div>
````````````````````````````````
However, a following blank line is needed, except at the end of
a document, and except for blocks of types 1--5, above:
```````````````````````````````` example
<div>
bar
</div>
*foo*
.
<div>
bar
</div>
*foo*
````````````````````````````````
HTML blocks of type 7 cannot interrupt a paragraph:
```````````````````````````````` example
Foo
<a href="bar">
baz
.
<p>Foo
<a href="bar">
baz</p>
````````````````````````````````
This rule differs from John Gruber's original Markdown syntax
specification, which says:
> The only restrictions are that block-level HTML elements —
> e.g. `<div>`, `<table>`, `<pre>`, `<p>`, etc. — must be separated from
> surrounding content by blank lines, and the start and end tags of the
> block should not be indented with tabs or spaces.
In some ways Gruber's rule is more restrictive than the one given
here:
- It requires that an HTML block be preceded by a blank line.
- It does not allow the start tag to be indented.
- It requires a matching end tag, which it also does not allow to
be indented.
Most Markdown implementations (including some of Gruber's own) do not
respect all of these restrictions.
There is one respect, however, in which Gruber's rule is more liberal
than the one given here, since it allows blank lines to occur inside
an HTML block. There are two reasons for disallowing them here.
First, it removes the need to parse balanced tags, which is
expensive and can require backtracking from the end of the document
if no matching end tag is found. Second, it provides a very simple
and flexible way of including Markdown content inside HTML tags:
simply separate the Markdown from the HTML using blank lines:
Compare:
```````````````````````````````` example
<div>
*Emphasized* text.
</div>
.
<div>
<p><em>Emphasized</em> text.</p>
</div>
````````````````````````````````
```````````````````````````````` example
<div>
*Emphasized* text.
</div>
.
<div>
*Emphasized* text.
</div>
````````````````````````````````
Some Markdown implementations have adopted a convention of
interpreting content inside tags as text if the open tag has
the attribute `markdown=1`. The rule given above seems a simpler and
more elegant way of achieving the same expressive power, which is also
much simpler to parse.
The main potential drawback is that one can no longer paste HTML
blocks into Markdown documents with 100% reliability. However,
*in most cases* this will work fine, because the blank lines in
HTML are usually followed by HTML block tags. For example:
```````````````````````````````` example
<table>
<tr>
<td>
Hi
</td>
</tr>
</table>
.
<table>
<tr>
<td>
Hi
</td>
</tr>
</table>
````````````````````````````````
There are problems, however, if the inner tags are indented
*and* separated by spaces, as then they will be interpreted as
an indented code block:
```````````````````````````````` example
<table>
<tr>
<td>
Hi
</td>
</tr>
</table>
.
<table>
<tr>
<pre><code>&lt;td&gt;
Hi
&lt;/td&gt;
</code></pre>
</tr>
</table>
````````````````````````````````
Fortunately, blank lines are usually not necessary and can be
deleted. The exception is inside `<pre>` tags, but as described
above, raw HTML blocks starting with `<pre>` *can* contain blank
lines.
## Link reference definitions
A [link reference definition](@)
consists of a [link label], indented up to three spaces, followed
by a colon (`:`), optional [whitespace] (including up to one
[line ending]), a [link destination],
optional [whitespace] (including up to one
[line ending]), and an optional [link
title], which if it is present must be separated
from the [link destination] by [whitespace].
No further [non-whitespace characters] may occur on the line.
A [link reference definition]
does not correspond to a structural element of a document. Instead, it
defines a label which can be used in [reference links]
and reference-style [images] elsewhere in the document. [Link
reference definitions] can come either before or after the links that use
them.
```````````````````````````````` example
[foo]: /url "title"
[foo]
.
<p><a href="/url" title="title">foo</a></p>
````````````````````````````````
```````````````````````````````` example
[foo]:
/url
'the title'
[foo]
.
<p><a href="/url" title="the title">foo</a></p>
````````````````````````````````
```````````````````````````````` example
[Foo*bar\]]:my_(url) 'title (with parens)'
[Foo*bar\]]
.
<p><a href="my_(url)" title="title (with parens)">Foo*bar]</a></p>
````````````````````````````````
```````````````````````````````` example
[Foo bar]:
<my%20url>
'title'
[Foo bar]
.
<p><a href="my%20url" title="title">Foo bar</a></p>
````````````````````````````````
The title may extend over multiple lines:
```````````````````````````````` example
[foo]: /url '
title
line1
line2
'
[foo]
.
<p><a href="/url" title="
title
line1
line2
">foo</a></p>
````````````````````````````````
However, it may not contain a [blank line]:
```````````````````````````````` example
[foo]: /url 'title
with blank line'
[foo]
.
<p>[foo]: /url 'title</p>
<p>with blank line'</p>
<p>[foo]</p>
````````````````````````````````
The title may be omitted:
```````````````````````````````` example
[foo]:
/url
[foo]
.
<p><a href="/url">foo</a></p>
````````````````````````````````
The link destination may not be omitted:
```````````````````````````````` example
[foo]:
[foo]
.
<p>[foo]:</p>
<p>[foo]</p>
````````````````````````````````
Both title and destination can contain backslash escapes
and literal backslashes:
```````````````````````````````` example
[foo]: /url\bar\*baz "foo\"bar\baz"
[foo]
.
<p><a href="/url%5Cbar*baz" title="foo&quot;bar\baz">foo</a></p>
````````````````````````````````
A link can come before its corresponding definition:
```````````````````````````````` example
[foo]
[foo]: url
.
<p><a href="url">foo</a></p>
````````````````````````````````
If there are several matching definitions, the first one takes
precedence:
```````````````````````````````` example
[foo]
[foo]: first
[foo]: second
.
<p><a href="first">foo</a></p>
````````````````````````````````
As noted in the section on [Links], matching of labels is
case-insensitive (see [matches]).
```````````````````````````````` example
[FOO]: /url
[Foo]
.
<p><a href="/url">Foo</a></p>
````````````````````````````````
```````````````````````````````` example
[ΑΓΩ]: /φου
[αγω]
.
<p><a href="/%CF%86%CE%BF%CF%85">αγω</a></p>
````````````````````````````````
Here is a link reference definition with no corresponding link.
It contributes nothing to the document.
```````````````````````````````` example
[foo]: /url
.
````````````````````````````````
Here is another one:
```````````````````````````````` example
[
foo
]: /url
bar
.
<p>bar</p>
````````````````````````````````
This is not a link reference definition, because there are
[non-whitespace characters] after the title:
```````````````````````````````` example
[foo]: /url "title" ok
.
<p>[foo]: /url &quot;title&quot; ok</p>
````````````````````````````````
This is a link reference definition, but it has no title:
```````````````````````````````` example
[foo]: /url
"title" ok
.
<p>&quot;title&quot; ok</p>
````````````````````````````````
This is not a link reference definition, because it is indented
four spaces:
```````````````````````````````` example
[foo]: /url "title"
[foo]
.
<pre><code>[foo]: /url &quot;title&quot;
</code></pre>
<p>[foo]</p>
````````````````````````````````
This is not a link reference definition, because it occurs inside
a code block:
```````````````````````````````` example
```
[foo]: /url
```
[foo]
.
<pre><code>[foo]: /url
</code></pre>
<p>[foo]</p>
````````````````````````````````
A [link reference definition] cannot interrupt a paragraph.
```````````````````````````````` example
Foo
[bar]: /baz
[bar]
.
<p>Foo
[bar]: /baz</p>
<p>[bar]</p>
````````````````````````````````
However, it can directly follow other block elements, such as headings
and thematic breaks, and it need not be followed by a blank line.
```````````````````````````````` example
# [Foo]
[foo]: /url
> bar
.
<h1><a href="/url">Foo</a></h1>
<blockquote>
<p>bar</p>
</blockquote>
````````````````````````````````
Several [link reference definitions]
can occur one after another, without intervening blank lines.
```````````````````````````````` example
[foo]: /foo-url "foo"
[bar]: /bar-url
"bar"
[baz]: /baz-url
[foo],
[bar],
[baz]
.
<p><a href="/foo-url" title="foo">foo</a>,
<a href="/bar-url" title="bar">bar</a>,
<a href="/baz-url">baz</a></p>
````````````````````````````````
[Link reference definitions] can occur
inside block containers, like lists and block quotations. They
affect the entire document, not just the container in which they
are defined:
```````````````````````````````` example
[foo]
> [foo]: /url
.
<p><a href="/url">foo</a></p>
<blockquote>
</blockquote>
````````````````````````````````
## Paragraphs
A sequence of non-blank lines that cannot be interpreted as other
kinds of blocks forms a [paragraph](@).
The contents of the paragraph are the result of parsing the
paragraph's raw content as inlines. The paragraph's raw content
is formed by concatenating the lines and removing initial and final
[whitespace].
A simple example with two paragraphs:
```````````````````````````````` example
aaa
bbb
.
<p>aaa</p>
<p>bbb</p>
````````````````````````````````
Paragraphs can contain multiple lines, but no blank lines:
```````````````````````````````` example
aaa
bbb
ccc
ddd
.
<p>aaa
bbb</p>
<p>ccc
ddd</p>
````````````````````````````````
Multiple blank lines between paragraph have no effect:
```````````````````````````````` example
aaa
bbb
.
<p>aaa</p>
<p>bbb</p>
````````````````````````````````
Leading spaces are skipped:
```````````````````````````````` example
aaa
bbb
.
<p>aaa
bbb</p>
````````````````````````````````
Lines after the first may be indented any amount, since indented
code blocks cannot interrupt paragraphs.
```````````````````````````````` example
aaa
bbb
ccc
.
<p>aaa
bbb
ccc</p>
````````````````````````````````
However, the first line may be indented at most three spaces,
or an indented code block will be triggered:
```````````````````````````````` example
aaa
bbb
.
<p>aaa
bbb</p>
````````````````````````````````
```````````````````````````````` example
aaa
bbb
.
<pre><code>aaa
</code></pre>
<p>bbb</p>
````````````````````````````````
Final spaces are stripped before inline parsing, so a paragraph
that ends with two or more spaces will not end with a [hard line
break]:
```````````````````````````````` example
aaa
bbb
.
<p>aaa<br />
bbb</p>
````````````````````````````````
## Blank lines
[Blank lines] between block-level elements are ignored,
except for the role they play in determining whether a [list]
is [tight] or [loose].
Blank lines at the beginning and end of the document are also ignored.
```````````````````````````````` example
aaa
# aaa
.
<p>aaa</p>
<h1>aaa</h1>
````````````````````````````````
# Container blocks
A [container block] is a block that has other
blocks as its contents. There are two basic kinds of container blocks:
[block quotes] and [list items].
[Lists] are meta-containers for [list items].
We define the syntax for container blocks recursively. The general
form of the definition is:
> If X is a sequence of blocks, then the result of
> transforming X in such-and-such a way is a container of type Y
> with these blocks as its content.
So, we explain what counts as a block quote or list item by explaining
how these can be *generated* from their contents. This should suffice
to define the syntax, although it does not give a recipe for *parsing*
these constructions. (A recipe is provided below in the section entitled
[A parsing strategy](#appendix-a-parsing-strategy).)
## Block quotes
A [block quote marker](@)
consists of 0-3 spaces of initial indent, plus (a) the character `>` together
with a following space, or (b) a single character `>` not followed by a space.
The following rules define [block quotes]:
1. **Basic case.** If a string of lines *Ls* constitute a sequence
of blocks *Bs*, then the result of prepending a [block quote
marker] to the beginning of each line in *Ls*
is a [block quote](#block-quotes) containing *Bs*.
2. **Laziness.** If a string of lines *Ls* constitute a [block
quote](#block-quotes) with contents *Bs*, then the result of deleting
the initial [block quote marker] from one or
more lines in which the next [non-whitespace character] after the [block
quote marker] is [paragraph continuation
text] is a block quote with *Bs* as its content.
[Paragraph continuation text](@) is text
that will be parsed as part of the content of a paragraph, but does
not occur at the beginning of the paragraph.
3. **Consecutiveness.** A document cannot contain two [block
quotes] in a row unless there is a [blank line] between them.
Nothing else counts as a [block quote](#block-quotes).
Here is a simple example:
```````````````````````````````` example
> # Foo
> bar
> baz
.
<blockquote>
<h1>Foo</h1>
<p>bar
baz</p>
</blockquote>
````````````````````````````````
The spaces after the `>` characters can be omitted:
```````````````````````````````` example
># Foo
>bar
> baz
.
<blockquote>
<h1>Foo</h1>
<p>bar
baz</p>
</blockquote>
````````````````````````````````
The `>` characters can be indented 1-3 spaces:
```````````````````````````````` example
> # Foo
> bar
> baz
.
<blockquote>
<h1>Foo</h1>
<p>bar
baz</p>
</blockquote>
````````````````````````````````
Four spaces gives us a code block:
```````````````````````````````` example
> # Foo
> bar
> baz
.
<pre><code>&gt; # Foo
&gt; bar
&gt; baz
</code></pre>
````````````````````````````````
The Laziness clause allows us to omit the `>` before
[paragraph continuation text]:
```````````````````````````````` example
> # Foo
> bar
baz
.
<blockquote>
<h1>Foo</h1>
<p>bar
baz</p>
</blockquote>
````````````````````````````````
A block quote can contain some lazy and some non-lazy
continuation lines:
```````````````````````````````` example
> bar
baz
> foo
.
<blockquote>
<p>bar
baz
foo</p>
</blockquote>
````````````````````````````````
Laziness only applies to lines that would have been continuations of
paragraphs had they been prepended with [block quote markers].
For example, the `> ` cannot be omitted in the second line of
``` markdown
> foo
> ---
```
without changing the meaning:
```````````````````````````````` example
> foo
---
.
<blockquote>
<p>foo</p>
</blockquote>
<hr />
````````````````````````````````
Similarly, if we omit the `> ` in the second line of
``` markdown
> - foo
> - bar
```
then the block quote ends after the first line:
```````````````````````````````` example
> - foo
- bar
.
<blockquote>
<ul>
<li>foo</li>
</ul>
</blockquote>
<ul>
<li>bar</li>
</ul>
````````````````````````````````
For the same reason, we can't omit the `> ` in front of
subsequent lines of an indented or fenced code block:
```````````````````````````````` example
> foo
bar
.
<blockquote>
<pre><code>foo
</code></pre>
</blockquote>
<pre><code>bar
</code></pre>
````````````````````````````````
```````````````````````````````` example
> ```
foo
```
.
<blockquote>
<pre><code></code></pre>
</blockquote>
<p>foo</p>
<pre><code></code></pre>
````````````````````````````````
Note that in the following case, we have a [lazy
continuation line]:
```````````````````````````````` example
> foo
- bar
.
<blockquote>
<p>foo
- bar</p>
</blockquote>
````````````````````````````````
To see why, note that in
```markdown
> foo
> - bar
```
the `- bar` is indented too far to start a list, and can't
be an indented code block because indented code blocks cannot
interrupt paragraphs, so it is [paragraph continuation text].
A block quote can be empty:
```````````````````````````````` example
>
.
<blockquote>
</blockquote>
````````````````````````````````
```````````````````````````````` example
>
>
>
.
<blockquote>
</blockquote>
````````````````````````````````
A block quote can have initial or final blank lines:
```````````````````````````````` example
>
> foo
>
.
<blockquote>
<p>foo</p>
</blockquote>
````````````````````````````````
A blank line always separates block quotes:
```````````````````````````````` example
> foo
> bar
.
<blockquote>
<p>foo</p>
</blockquote>
<blockquote>
<p>bar</p>
</blockquote>
````````````````````````````````
(Most current Markdown implementations, including John Gruber's
original `Markdown.pl`, will parse this example as a single block quote
with two paragraphs. But it seems better to allow the author to decide
whether two block quotes or one are wanted.)
Consecutiveness means that if we put these block quotes together,
we get a single block quote:
```````````````````````````````` example
> foo
> bar
.
<blockquote>
<p>foo
bar</p>
</blockquote>
````````````````````````````````
To get a block quote with two paragraphs, use:
```````````````````````````````` example
> foo
>
> bar
.
<blockquote>
<p>foo</p>
<p>bar</p>
</blockquote>
````````````````````````````````
Block quotes can interrupt paragraphs:
```````````````````````````````` example
foo
> bar
.
<p>foo</p>
<blockquote>
<p>bar</p>
</blockquote>
````````````````````````````````
In general, blank lines are not needed before or after block
quotes:
```````````````````````````````` example
> aaa
***
> bbb
.
<blockquote>
<p>aaa</p>
</blockquote>
<hr />
<blockquote>
<p>bbb</p>
</blockquote>
````````````````````````````````
However, because of laziness, a blank line is needed between
a block quote and a following paragraph:
```````````````````````````````` example
> bar
baz
.
<blockquote>
<p>bar
baz</p>
</blockquote>
````````````````````````````````
```````````````````````````````` example
> bar
baz
.
<blockquote>
<p>bar</p>
</blockquote>
<p>baz</p>
````````````````````````````````
```````````````````````````````` example
> bar
>
baz
.
<blockquote>
<p>bar</p>
</blockquote>
<p>baz</p>
````````````````````````````````
It is a consequence of the Laziness rule that any number
of initial `>`s may be omitted on a continuation line of a
nested block quote:
```````````````````````````````` example
> > > foo
bar
.
<blockquote>
<blockquote>
<blockquote>
<p>foo
bar</p>
</blockquote>
</blockquote>
</blockquote>
````````````````````````````````
```````````````````````````````` example
>>> foo
> bar
>>baz
.
<blockquote>
<blockquote>
<blockquote>
<p>foo
bar
baz</p>
</blockquote>
</blockquote>
</blockquote>
````````````````````````````````
When including an indented code block in a block quote,
remember that the [block quote marker] includes
both the `>` and a following space. So *five spaces* are needed after
the `>`:
```````````````````````````````` example
> code
> not code
.
<blockquote>
<pre><code>code
</code></pre>
</blockquote>
<blockquote>
<p>not code</p>
</blockquote>
````````````````````````````````
## List items
A [list marker](@) is a
[bullet list marker] or an [ordered list marker].
A [bullet list marker](@)
is a `-`, `+`, or `*` character.
An [ordered list marker](@)
is a sequence of 1--9 arabic digits (`0-9`), followed by either a
`.` character or a `)` character. (The reason for the length
limit is that with 10 digits we start seeing integer overflows
in some browsers.)
The following rules define [list items]:
1. **Basic case.** If a sequence of lines *Ls* constitute a sequence of
blocks *Bs* starting with a [non-whitespace character] and not separated
from each other by more than one blank line, and *M* is a list
marker of width *W* followed by 1 ≤ *N* ≤ 4 spaces, then the result
of prepending *M* and the following spaces to the first line of
*Ls*, and indenting subsequent lines of *Ls* by *W + N* spaces, is a
list item with *Bs* as its contents. The type of the list item
(bullet or ordered) is determined by the type of its list marker.
If the list item is ordered, then it is also assigned a start
number, based on the ordered list marker.
Exceptions: When the first list item in a [list] interrupts
a paragraph---that is, when it starts on a line that would
otherwise count as [paragraph continuation text]---then (a)
the lines *Ls* must not begin with a blank line, and (b) if
the list item is ordered, the start number must be 1.
For example, let *Ls* be the lines
```````````````````````````````` example
A paragraph
with two lines.
indented code
> A block quote.
.
<p>A paragraph
with two lines.</p>
<pre><code>indented code
</code></pre>
<blockquote>
<p>A block quote.</p>
</blockquote>
````````````````````````````````
And let *M* be the marker `1.`, and *N* = 2. Then rule #1 says
that the following is an ordered list item with start number 1,
and the same contents as *Ls*:
```````````````````````````````` example
1. A paragraph
with two lines.
indented code
> A block quote.
.
<ol>
<li>
<p>A paragraph
with two lines.</p>
<pre><code>indented code
</code></pre>
<blockquote>
<p>A block quote.</p>
</blockquote>
</li>
</ol>
````````````````````````````````
The most important thing to notice is that the position of
the text after the list marker determines how much indentation
is needed in subsequent blocks in the list item. If the list
marker takes up two spaces, and there are three spaces between
the list marker and the next [non-whitespace character], then blocks
must be indented five spaces in order to fall under the list
item.
Here are some examples showing how far content must be indented to be
put under the list item:
```````````````````````````````` example
- one
two
.
<ul>
<li>one</li>
</ul>
<p>two</p>
````````````````````````````````
```````````````````````````````` example
- one
two
.
<ul>
<li>
<p>one</p>
<p>two</p>
</li>
</ul>
````````````````````````````````
```````````````````````````````` example
- one
two
.
<ul>
<li>one</li>
</ul>
<pre><code> two
</code></pre>
````````````````````````````````
```````````````````````````````` example
- one
two
.
<ul>
<li>
<p>one</p>
<p>two</p>
</li>
</ul>
````````````````````````````````
It is tempting to think of this in terms of columns: the continuation
blocks must be indented at least to the column of the first
[non-whitespace character] after the list marker. However, that is not quite right.
The spaces after the list marker determine how much relative indentation
is needed. Which column this indentation reaches will depend on
how the list item is embedded in other constructions, as shown by
this example:
```````````````````````````````` example
> > 1. one
>>
>> two
.
<blockquote>
<blockquote>
<ol>
<li>
<p>one</p>
<p>two</p>
</li>
</ol>
</blockquote>
</blockquote>
````````````````````````````````
Here `two` occurs in the same column as the list marker `1.`,
but is actually contained in the list item, because there is
sufficient indentation after the last containing blockquote marker.
The converse is also possible. In the following example, the word `two`
occurs far to the right of the initial text of the list item, `one`, but
it is not considered part of the list item, because it is not indented
far enough past the blockquote marker:
```````````````````````````````` example
>>- one
>>
> > two
.
<blockquote>
<blockquote>
<ul>
<li>one</li>
</ul>
<p>two</p>
</blockquote>
</blockquote>
````````````````````````````````
Note that at least one space is needed between the list marker and
any following content, so these are not list items:
```````````````````````````````` example
-one
2.two
.
<p>-one</p>
<p>2.two</p>
````````````````````````````````
A list item may contain blocks that are separated by more than
one blank line.
```````````````````````````````` example
- foo
bar
.
<ul>
<li>
<p>foo</p>
<p>bar</p>
</li>
</ul>
````````````````````````````````
A list item may contain any kind of block:
```````````````````````````````` example
1. foo
```
bar
```
baz
> bam
.
<ol>
<li>
<p>foo</p>
<pre><code>bar
</code></pre>
<p>baz</p>
<blockquote>
<p>bam</p>
</blockquote>
</li>
</ol>
````````````````````````````````
A list item that contains an indented code block will preserve
empty lines within the code block verbatim.
```````````````````````````````` example
- Foo
bar
baz
.
<ul>
<li>
<p>Foo</p>
<pre><code>bar
baz
</code></pre>
</li>
</ul>
````````````````````````````````
Note that ordered list start numbers must be nine digits or less:
```````````````````````````````` example
123456789. ok
.
<ol start="123456789">
<li>ok</li>
</ol>
````````````````````````````````
```````````````````````````````` example
1234567890. not ok
.
<p>1234567890. not ok</p>
````````````````````````````````
A start number may begin with 0s:
```````````````````````````````` example
0. ok
.
<ol start="0">
<li>ok</li>
</ol>
````````````````````````````````
```````````````````````````````` example
003. ok
.
<ol start="3">
<li>ok</li>
</ol>
````````````````````````````````
A start number may not be negative:
```````````````````````````````` example
-1. not ok
.
<p>-1. not ok</p>
````````````````````````````````
2. **Item starting with indented code.** If a sequence of lines *Ls*
constitute a sequence of blocks *Bs* starting with an indented code
block and not separated from each other by more than one blank line,
and *M* is a list marker of width *W* followed by
one space, then the result of prepending *M* and the following
space to the first line of *Ls*, and indenting subsequent lines of
*Ls* by *W + 1* spaces, is a list item with *Bs* as its contents.
If a line is empty, then it need not be indented. The type of the
list item (bullet or ordered) is determined by the type of its list
marker. If the list item is ordered, then it is also assigned a
start number, based on the ordered list marker.
An indented code block will have to be indented four spaces beyond
the edge of the region where text will be included in the list item.
In the following case that is 6 spaces:
```````````````````````````````` example
- foo
bar
.
<ul>
<li>
<p>foo</p>
<pre><code>bar
</code></pre>
</li>
</ul>
````````````````````````````````
And in this case it is 11 spaces:
```````````````````````````````` example
10. foo
bar
.
<ol start="10">
<li>
<p>foo</p>
<pre><code>bar
</code></pre>
</li>
</ol>
````````````````````````````````
If the *first* block in the list item is an indented code block,
then by rule #2, the contents must be indented *one* space after the
list marker:
```````````````````````````````` example
indented code
paragraph
more code
.
<pre><code>indented code
</code></pre>
<p>paragraph</p>
<pre><code>more code
</code></pre>
````````````````````````````````
```````````````````````````````` example
1. indented code
paragraph
more code
.
<ol>
<li>
<pre><code>indented code
</code></pre>
<p>paragraph</p>
<pre><code>more code
</code></pre>
</li>
</ol>
````````````````````````````````
Note that an additional space indent is interpreted as space
inside the code block:
```````````````````````````````` example
1. indented code
paragraph
more code
.
<ol>
<li>
<pre><code> indented code
</code></pre>
<p>paragraph</p>
<pre><code>more code
</code></pre>
</li>
</ol>
````````````````````````````````
Note that rules #1 and #2 only apply to two cases: (a) cases
in which the lines to be included in a list item begin with a
[non-whitespace character], and (b) cases in which
they begin with an indented code
block. In a case like the following, where the first block begins with
a three-space indent, the rules do not allow us to form a list item by
indenting the whole thing and prepending a list marker:
```````````````````````````````` example
foo
bar
.
<p>foo</p>
<p>bar</p>
````````````````````````````````
```````````````````````````````` example
- foo
bar
.
<ul>
<li>foo</li>
</ul>
<p>bar</p>
````````````````````````````````
This is not a significant restriction, because when a block begins
with 1-3 spaces indent, the indentation can always be removed without
a change in interpretation, allowing rule #1 to be applied. So, in
the above case:
```````````````````````````````` example
- foo
bar
.
<ul>
<li>
<p>foo</p>
<p>bar</p>
</li>
</ul>
````````````````````````````````
3. **Item starting with a blank line.** If a sequence of lines *Ls*
starting with a single [blank line] constitute a (possibly empty)
sequence of blocks *Bs*, not separated from each other by more than
one blank line, and *M* is a list marker of width *W*,
then the result of prepending *M* to the first line of *Ls*, and
indenting subsequent lines of *Ls* by *W + 1* spaces, is a list
item with *Bs* as its contents.
If a line is empty, then it need not be indented. The type of the
list item (bullet or ordered) is determined by the type of its list
marker. If the list item is ordered, then it is also assigned a
start number, based on the ordered list marker.
Here are some list items that start with a blank line but are not empty:
```````````````````````````````` example
-
foo
-
```
bar
```
-
baz
.
<ul>
<li>foo</li>
<li>
<pre><code>bar
</code></pre>
</li>
<li>
<pre><code>baz
</code></pre>
</li>
</ul>
````````````````````````````````
When the list item starts with a blank line, the number of spaces
following the list marker doesn't change the required indentation:
```````````````````````````````` example
-
foo
.
<ul>
<li>foo</li>
</ul>
````````````````````````````````
A list item can begin with at most one blank line.
In the following example, `foo` is not part of the list
item:
```````````````````````````````` example
-
foo
.
<ul>
<li></li>
</ul>
<p>foo</p>
````````````````````````````````
Here is an empty bullet list item:
```````````````````````````````` example
- foo
-
- bar
.
<ul>
<li>foo</li>
<li></li>
<li>bar</li>
</ul>
````````````````````````````````
It does not matter whether there are spaces following the [list marker]:
```````````````````````````````` example
- foo
-
- bar
.
<ul>
<li>foo</li>
<li></li>
<li>bar</li>
</ul>
````````````````````````````````
Here is an empty ordered list item:
```````````````````````````````` example
1. foo
2.
3. bar
.
<ol>
<li>foo</li>
<li></li>
<li>bar</li>
</ol>
````````````````````````````````
A list may start or end with an empty list item:
```````````````````````````````` example
*
.
<ul>
<li></li>
</ul>
````````````````````````````````
However, an empty list item cannot interrupt a paragraph:
```````````````````````````````` example
foo
*
foo
1.
.
<p>foo
*</p>
<p>foo
1.</p>
````````````````````````````````
4. **Indentation.** If a sequence of lines *Ls* constitutes a list item
according to rule #1, #2, or #3, then the result of indenting each line
of *Ls* by 1-3 spaces (the same for each line) also constitutes a
list item with the same contents and attributes. If a line is
empty, then it need not be indented.
Indented one space:
```````````````````````````````` example
1. A paragraph
with two lines.
indented code
> A block quote.
.
<ol>
<li>
<p>A paragraph
with two lines.</p>
<pre><code>indented code
</code></pre>
<blockquote>
<p>A block quote.</p>
</blockquote>
</li>
</ol>
````````````````````````````````
Indented two spaces:
```````````````````````````````` example
1. A paragraph
with two lines.
indented code
> A block quote.
.
<ol>
<li>
<p>A paragraph
with two lines.</p>
<pre><code>indented code
</code></pre>
<blockquote>
<p>A block quote.</p>
</blockquote>
</li>
</ol>
````````````````````````````````
Indented three spaces:
```````````````````````````````` example
1. A paragraph
with two lines.
indented code
> A block quote.
.
<ol>
<li>
<p>A paragraph
with two lines.</p>
<pre><code>indented code
</code></pre>
<blockquote>
<p>A block quote.</p>
</blockquote>
</li>
</ol>
````````````````````````````````
Four spaces indent gives a code block:
```````````````````````````````` example
1. A paragraph
with two lines.
indented code
> A block quote.
.
<pre><code>1. A paragraph
with two lines.
indented code
&gt; A block quote.
</code></pre>
````````````````````````````````
5. **Laziness.** If a string of lines *Ls* constitute a [list
item](#list-items) with contents *Bs*, then the result of deleting
some or all of the indentation from one or more lines in which the
next [non-whitespace character] after the indentation is
[paragraph continuation text] is a
list item with the same contents and attributes. The unindented
lines are called
[lazy continuation line](@)s.
Here is an example with [lazy continuation lines]:
```````````````````````````````` example
1. A paragraph
with two lines.
indented code
> A block quote.
.
<ol>
<li>
<p>A paragraph
with two lines.</p>
<pre><code>indented code
</code></pre>
<blockquote>
<p>A block quote.</p>
</blockquote>
</li>
</ol>
````````````````````````````````
Indentation can be partially deleted:
```````````````````````````````` example
1. A paragraph
with two lines.
.
<ol>
<li>A paragraph
with two lines.</li>
</ol>
````````````````````````````````
These examples show how laziness can work in nested structures:
```````````````````````````````` example
> 1. > Blockquote
continued here.
.
<blockquote>
<ol>
<li>
<blockquote>
<p>Blockquote
continued here.</p>
</blockquote>
</li>
</ol>
</blockquote>
````````````````````````````````
```````````````````````````````` example
> 1. > Blockquote
> continued here.
.
<blockquote>
<ol>
<li>
<blockquote>
<p>Blockquote
continued here.</p>
</blockquote>
</li>
</ol>
</blockquote>
````````````````````````````````
6. **That's all.** Nothing that is not counted as a list item by rules
#1--5 counts as a [list item](#list-items).
The rules for sublists follow from the general rules above. A sublist
must be indented the same number of spaces a paragraph would need to be
in order to be included in the list item.
So, in this case we need two spaces indent:
```````````````````````````````` example
- foo
- bar
- baz
- boo
.
<ul>
<li>foo
<ul>
<li>bar
<ul>
<li>baz
<ul>
<li>boo</li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>
````````````````````````````````
One is not enough:
```````````````````````````````` example
- foo
- bar
- baz
- boo
.
<ul>
<li>foo</li>
<li>bar</li>
<li>baz</li>
<li>boo</li>
</ul>
````````````````````````````````
Here we need four, because the list marker is wider:
```````````````````````````````` example
10) foo
- bar
.
<ol start="10">
<li>foo
<ul>
<li>bar</li>
</ul>
</li>
</ol>
````````````````````````````````
Three is not enough:
```````````````````````````````` example
10) foo
- bar
.
<ol start="10">
<li>foo</li>
</ol>
<ul>
<li>bar</li>
</ul>
````````````````````````````````
A list may be the first block in a list item:
```````````````````````````````` example
- - foo
.
<ul>
<li>
<ul>
<li>foo</li>
</ul>
</li>
</ul>
````````````````````````````````
```````````````````````````````` example
1. - 2. foo
.
<ol>
<li>
<ul>
<li>
<ol start="2">
<li>foo</li>
</ol>
</li>
</ul>
</li>
</ol>
````````````````````````````````
A list item can contain a heading:
```````````````````````````````` example
- # Foo
- Bar
---
baz
.
<ul>
<li>
<h1>Foo</h1>
</li>
<li>
<h2>Bar</h2>
baz</li>
</ul>
````````````````````````````````
### Motivation
John Gruber's Markdown spec says the following about list items:
1. "List markers typically start at the left margin, but may be indented
by up to three spaces. List markers must be followed by one or more
spaces or a tab."
2. "To make lists look nice, you can wrap items with hanging indents....
But if you don't want to, you don't have to."
3. "List items may consist of multiple paragraphs. Each subsequent
paragraph in a list item must be indented by either 4 spaces or one
tab."
4. "It looks nice if you indent every line of the subsequent paragraphs,
but here again, Markdown will allow you to be lazy."
5. "To put a blockquote within a list item, the blockquote's `>`
delimiters need to be indented."
6. "To put a code block within a list item, the code block needs to be
indented twice — 8 spaces or two tabs."
These rules specify that a paragraph under a list item must be indented
four spaces (presumably, from the left margin, rather than the start of
the list marker, but this is not said), and that code under a list item
must be indented eight spaces instead of the usual four. They also say
that a block quote must be indented, but not by how much; however, the
example given has four spaces indentation. Although nothing is said
about other kinds of block-level content, it is certainly reasonable to
infer that *all* block elements under a list item, including other
lists, must be indented four spaces. This principle has been called the
*four-space rule*.
The four-space rule is clear and principled, and if the reference
implementation `Markdown.pl` had followed it, it probably would have
become the standard. However, `Markdown.pl` allowed paragraphs and
sublists to start with only two spaces indentation, at least on the
outer level. Worse, its behavior was inconsistent: a sublist of an
outer-level list needed two spaces indentation, but a sublist of this
sublist needed three spaces. It is not surprising, then, that different
implementations of Markdown have developed very different rules for
determining what comes under a list item. (Pandoc and python-Markdown,
for example, stuck with Gruber's syntax description and the four-space
rule, while discount, redcarpet, marked, PHP Markdown, and others
followed `Markdown.pl`'s behavior more closely.)
Unfortunately, given the divergences between implementations, there
is no way to give a spec for list items that will be guaranteed not
to break any existing documents. However, the spec given here should
correctly handle lists formatted with either the four-space rule or
the more forgiving `Markdown.pl` behavior, provided they are laid out
in a way that is natural for a human to read.
The strategy here is to let the width and indentation of the list marker
determine the indentation necessary for blocks to fall under the list
item, rather than having a fixed and arbitrary number. The writer can
think of the body of the list item as a unit which gets indented to the
right enough to fit the list marker (and any indentation on the list
marker). (The laziness rule, #5, then allows continuation lines to be
unindented if needed.)
This rule is superior, we claim, to any rule requiring a fixed level of
indentation from the margin. The four-space rule is clear but
unnatural. It is quite unintuitive that
``` markdown
- foo
bar
- baz
```
should be parsed as two lists with an intervening paragraph,
``` html
<ul>
<li>foo</li>
</ul>
<p>bar</p>
<ul>
<li>baz</li>
</ul>
```
as the four-space rule demands, rather than a single list,
``` html
<ul>
<li>
<p>foo</p>
<p>bar</p>
<ul>
<li>baz</li>
</ul>
</li>
</ul>
```
The choice of four spaces is arbitrary. It can be learned, but it is
not likely to be guessed, and it trips up beginners regularly.
Would it help to adopt a two-space rule? The problem is that such
a rule, together with the rule allowing 1--3 spaces indentation of the
initial list marker, allows text that is indented *less than* the
original list marker to be included in the list item. For example,
`Markdown.pl` parses
``` markdown
- one
two
```
as a single list item, with `two` a continuation paragraph:
``` html
<ul>
<li>
<p>one</p>
<p>two</p>
</li>
</ul>
```
and similarly
``` markdown
> - one
>
> two
```
as
``` html
<blockquote>
<ul>
<li>
<p>one</p>
<p>two</p>
</li>
</ul>
</blockquote>
```
This is extremely unintuitive.
Rather than requiring a fixed indent from the margin, we could require
a fixed indent (say, two spaces, or even one space) from the list marker (which
may itself be indented). This proposal would remove the last anomaly
discussed. Unlike the spec presented above, it would count the following
as a list item with a subparagraph, even though the paragraph `bar`
is not indented as far as the first paragraph `foo`:
``` markdown
10. foo
bar
```
Arguably this text does read like a list item with `bar` as a subparagraph,
which may count in favor of the proposal. However, on this proposal indented
code would have to be indented six spaces after the list marker. And this
would break a lot of existing Markdown, which has the pattern:
``` markdown
1. foo
indented code
```
where the code is indented eight spaces. The spec above, by contrast, will
parse this text as expected, since the code block's indentation is measured
from the beginning of `foo`.
The one case that needs special treatment is a list item that *starts*
with indented code. How much indentation is required in that case, since
we don't have a "first paragraph" to measure from? Rule #2 simply stipulates
that in such cases, we require one space indentation from the list marker
(and then the normal four spaces for the indented code). This will match the
four-space rule in cases where the list marker plus its initial indentation
takes four spaces (a common case), but diverge in other cases.
## Lists
A [list](@) is a sequence of one or more
list items [of the same type]. The list items
may be separated by any number of blank lines.
Two list items are [of the same type](@)
if they begin with a [list marker] of the same type.
Two list markers are of the
same type if (a) they are bullet list markers using the same character
(`-`, `+`, or `*`) or (b) they are ordered list numbers with the same
delimiter (either `.` or `)`).
A list is an [ordered list](@)
if its constituent list items begin with
[ordered list markers], and a
[bullet list](@) if its constituent list
items begin with [bullet list markers].
The [start number](@)
of an [ordered list] is determined by the list number of
its initial list item. The numbers of subsequent list items are
disregarded.
A list is [loose](@) if any of its constituent
list items are separated by blank lines, or if any of its constituent
list items directly contain two block-level elements with a blank line
between them. Otherwise a list is [tight](@).
(The difference in HTML output is that paragraphs in a loose list are
wrapped in `<p>` tags, while paragraphs in a tight list are not.)
Changing the bullet or ordered list delimiter starts a new list:
```````````````````````````````` example
- foo
- bar
+ baz
.
<ul>
<li>foo</li>
<li>bar</li>
</ul>
<ul>
<li>baz</li>
</ul>
````````````````````````````````
```````````````````````````````` example
1. foo
2. bar
3) baz
.
<ol>
<li>foo</li>
<li>bar</li>
</ol>
<ol start="3">
<li>baz</li>
</ol>
````````````````````````````````
In CommonMark, a list can interrupt a paragraph. That is,
no blank line is needed to separate a paragraph from a following
list:
```````````````````````````````` example
Foo
- bar
- baz
.
<p>Foo</p>
<ul>
<li>bar</li>
<li>baz</li>
</ul>
````````````````````````````````
`Markdown.pl` does not allow this, through fear of triggering a list
via a numeral in a hard-wrapped line:
``` markdown
The number of windows in my house is
14. The number of doors is 6.
```
Oddly, though, `Markdown.pl` *does* allow a blockquote to
interrupt a paragraph, even though the same considerations might
apply.
In CommonMark, we do allow lists to interrupt paragraphs, for
two reasons. First, it is natural and not uncommon for people
to start lists without blank lines:
``` markdown
I need to buy
- new shoes
- a coat
- a plane ticket
```
Second, we are attracted to a
> [principle of uniformity](@):
> if a chunk of text has a certain
> meaning, it will continue to have the same meaning when put into a
> container block (such as a list item or blockquote).
(Indeed, the spec for [list items] and [block quotes] presupposes
this principle.) This principle implies that if
``` markdown
* I need to buy
- new shoes
- a coat
- a plane ticket
```
is a list item containing a paragraph followed by a nested sublist,
as all Markdown implementations agree it is (though the paragraph
may be rendered without `<p>` tags, since the list is "tight"),
then
``` markdown
I need to buy
- new shoes
- a coat
- a plane ticket
```
by itself should be a paragraph followed by a nested sublist.
Since it is well established Markdown practice to allow lists to
interrupt paragraphs inside list items, the [principle of
uniformity] requires us to allow this outside list items as
well. ([reStructuredText](http://docutils.sourceforge.net/rst.html)
takes a different approach, requiring blank lines before lists
even inside other list items.)
In order to solve of unwanted lists in paragraphs with
hard-wrapped numerals, we allow only lists starting with `1` to
interrupt paragraphs. Thus,
```````````````````````````````` example
The number of windows in my house is
14. The number of doors is 6.
.
<p>The number of windows in my house is
14. The number of doors is 6.</p>
````````````````````````````````
We may still get an unintended result in cases like
```````````````````````````````` example
The number of windows in my house is
1. The number of doors is 6.
.
<p>The number of windows in my house is</p>
<ol>
<li>The number of doors is 6.</li>
</ol>
````````````````````````````````
but this rule should prevent most spurious list captures.
There can be any number of blank lines between items:
```````````````````````````````` example
- foo
- bar
- baz
.