GitLab Flavored Markdown Internal Extensions

Version alpha

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 general category, 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 !, ", #, $, %, &, ', (, ), *, +, ,, -, ., / (U+0021–2F), :, ;, <, =, >, ?, @ (U+003A–0040), [, \, ], ^, _, ` (U+005B–0060), {, |, }, or ~ (U+007B–007E).

A punctuation character is an [ASCII punctuation character] or anything in the general Unicode categories 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 1
→foo→baz→→bim
<pre><code>foo→baz→→bim
</code></pre>
Example 2
  →foo→baz→→bim
<pre><code>foo→baz→→bim
</code></pre>
Example 3
    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 4
  - foo

→bar
<ul>
<li>
<p>foo</p>
<p>bar</p>
</li>
</ul>
Example 5
- 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 three spaces. Since one of these spaces is considered part of the delimiter, foo is considered to be indented six spaces inside the block quote context, so we get an indented code block starting with two spaces.

Example 6
>→→foo
<blockquote>
<pre><code>  foo
</code></pre>
</blockquote>
Example 7
-→→foo
<ul>
<li>
<pre><code>  foo
</code></pre>
</li>
</ul>
Example 8
    foo
→bar
<pre><code>foo
bar
</code></pre>
Example 9
 - foo
   - bar
→ - baz
<ul>
<li>foo
<ul>
<li>bar
<ul>
<li>baz</li>
</ul>
</li>
</ul>
</li>
</ul>
Example 10
#→Foo
<h1>Foo</h1>
Example 11
*→*→*→
<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 spans, 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 12
- `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 blocks, which can contain other blocks, and leaf blocks, 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 or tabs, forms a thematic break.

Example 13
***
---
___
<hr />
<hr />
<hr />

Wrong characters:

Example 14
+++
<p>+++</p>
Example 15
===
<p>===</p>

Not enough characters:

Example 16
--
**
__
<p>--
**
__</p>

One to three spaces indent are allowed:

Example 17
 ***
  ***
   ***
<hr />
<hr />
<hr />

Four spaces is too many:

Example 18
    ***
<pre><code>***
</code></pre>
Example 19
Foo
    ***
<p>Foo
***</p>

More than three characters may be used:

Example 20
_____________________________________
<hr />

Spaces are allowed between the characters:

Example 21
 - - -
<hr />
Example 22
 **  * ** * ** * **
<hr />
Example 23
-     -      -      -
<hr />

Spaces are allowed at the end:

Example 24
- - - -    
<hr />

However, no other characters may occur in the line:

Example 25
_ _ _ _ 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 26
 *-*
<p><em>-</em></p>

Thematic breaks do not need blank lines before or after:

Example 27
- foo
***
- bar
<ul>
<li>foo</li>
</ul>
<hr />
<ul>
<li>bar</li>
</ul>

Thematic breaks can interrupt a paragraph:

Example 28
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 29
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 30
* 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 31
- 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 32
# 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 33
####### 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, and it helps prevent things like the following from being parsed as headings:

Example 34
#5 bolt

#hashtag
<p>#5 bolt</p>
<p>#hashtag</p>

This is not a heading, because the first # is escaped:

Example 35
\## foo
<p>## foo</p>

Contents are parsed as inlines:

Example 36
# foo *bar* \*baz\*
<h1>foo <em>bar</em> *baz*</h1>

Leading and trailing [whitespace] is ignored in parsing inline content:

Example 37
#                  foo                     
<h1>foo</h1>

One to three spaces indentation are allowed:

Example 38
 ### foo
  ## foo
   # foo
<h3>foo</h3>
<h2>foo</h2>
<h1>foo</h1>

Four spaces are too much:

Example 39
    # foo
<pre><code># foo
</code></pre>
Example 40
foo
    # bar
<p>foo
# bar</p>

A closing sequence of # characters is optional:

Example 41
## foo ##
  ###   bar    ###
<h2>foo</h2>
<h3>bar</h3>

It need not be the same length as the opening sequence:

Example 42
# foo ##################################
##### foo ##
<h1>foo</h1>
<h5>foo</h5>

Spaces are allowed after the closing sequence:

Example 43
### 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 44
### foo ### b
<h3>foo ### b</h3>

The closing sequence must be preceded by a space:

Example 45
# foo#
<h1>foo#</h1>

Backslash-escaped # characters do not count as part of the closing sequence:

Example 46
### 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 47
****
## foo
****
<hr />
<h2>foo</h2>
<hr />
Example 48
Foo bar
# baz
Bar foo
<p>Foo bar</p>
<h1>baz</h1>
<p>Bar foo</p>

ATX headings can be empty:

Example 49
## 
#
### ###
<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 50
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 51
Foo *bar
baz*
====
<h1>Foo <em>bar
baz</em></h1>

The contents are the result of parsing the headings's raw content as inlines. The heading's raw content is formed by concatenating the lines and removing initial and final [whitespace].

Example 52
  Foo *bar
baz*→
====
<h1>Foo <em>bar
baz</em></h1>

The underlining can be any length:

Example 53
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 54
   Foo
---

  Foo
-----

  Foo
  ===
<h2>Foo</h2>
<h2>Foo</h2>
<h1>Foo</h1>

Four spaces indent is too much:

Example 55
    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 56
Foo
   ----      
<h2>Foo</h2>

Four spaces is too much:

Example 57
Foo
    ---
<p>Foo
---</p>

The setext heading underline cannot contain internal spaces:

Example 58
Foo
= =

Foo
--- -
<p>Foo
= =</p>
<p>Foo</p>
<hr />

Trailing spaces in the content line do not cause a line break:

Example 59
Foo  
-----
<h2>Foo</h2>

Nor does a backslash at the end:

Example 60
Foo\
----
<h2>Foo\</h2>

Since indicators of block structure take precedence over indicators of inline structure, the following are setext headings:

Example 61
`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 62
> Foo
---
<blockquote>
<p>Foo</p>
</blockquote>
<hr />
Example 63
> foo
bar
===
<blockquote>
<p>foo
bar
===</p>
</blockquote>
Example 64
- 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 65
Foo
Bar
---
<h2>Foo
Bar</h2>

But in general a blank line is not required before or after setext headings:

Example 66
---
Foo
---
Bar
---
Baz
<hr />
<h2>Foo</h2>
<h2>Bar</h2>
<p>Baz</p>

Setext headings cannot be empty:

Example 67

====
<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 68
---
---
<hr />
<hr />
Example 69
- foo
-----
<ul>
<li>foo</li>
</ul>
<hr />
Example 70
    foo
---
<pre><code>foo
</code></pre>
<hr />
Example 71
> foo
-----
<blockquote>
<p>foo</p>
</blockquote>
<hr />

If you want a heading with > foo as its literal text, you can use backslash escapes:

Example 72
\> 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

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 73
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 74
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 75
Foo
bar
* * *
baz
<p>Foo
bar</p>
<hr />
<p>baz</p>

Authors who want interpretation 3 can use backslash escapes:

Example 76
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 77
    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 78
  - foo

    bar
<ul>
<li>
<p>foo</p>
<p>bar</p>
</li>
</ul>
Example 79
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 80
    <a/>
    *hi*

    - one
<pre><code>&lt;a/&gt;
*hi*

- one
</code></pre>

Here we have three chunks separated by blank lines:

Example 81
    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 82
    chunk1
      
      chunk2
<pre><code>chunk1
  
  chunk2
</code></pre>

An indented code block cannot interrupt a paragraph. (This allows hanging indents and the like.)

Example 83
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 84
    foo
bar
<pre><code>foo
</code></pre>
<p>bar</p>

And indented code can occur immediately before and after other kinds of blocks:

Example 85
# 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 86
        foo
    bar
<pre><code>    foo
bar
</code></pre>

Blank lines preceding or following an indented code block are not included in it:

Example 87

    
    foo
    
<pre><code>foo
</code></pre>

Trailing spaces are included in the code block's content:

Example 88
    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 whitespace and called the info string. If the [info string] comes after a backtick fence, it 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 89
```
<
 >
```
<pre><code>&lt;
 &gt;
</code></pre>

With tildes:

Example 90
~~~
<
 >
~~~
<pre><code>&lt;
 &gt;
</code></pre>

Fewer than three backticks is not enough:

Example 91
``
foo
``
<p><code>foo</code></p>

The closing code fence must use the same character as the opening fence:

Example 92
```
aaa
~~~
```
<pre><code>aaa
~~~
</code></pre>
Example 93
~~~
aaa
```
~~~
<pre><code>aaa
```
</code></pre>

The closing code fence must be at least as long as the opening fence:

Example 94
````
aaa
```
``````
<pre><code>aaa
```
</code></pre>
Example 95
~~~~
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 96
```
<pre><code></code></pre>
Example 97
`````

```
aaa
<pre><code>
```
aaa
</code></pre>
Example 98
> ```
> aaa

bbb
<blockquote>
<pre><code>aaa
</code></pre>
</blockquote>
<p>bbb</p>

A code block can have all empty lines as its content:

Example 99
```

  
```
<pre><code>
  
</code></pre>

A code block can be empty:

Example 100
```
```
<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 101
 ```
 aaa
aaa
```
<pre><code>aaa
aaa
</code></pre>
Example 102
  ```
aaa
  aaa
aaa
  ```
<pre><code>aaa
aaa
aaa
</code></pre>
Example 103
   ```
   aaa
    aaa
  aaa
   ```
<pre><code>aaa
 aaa
aaa
</code></pre>

Four spaces indentation produces an indented code block:

Example 104
    ```
    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 105
```
aaa
  ```
<pre><code>aaa
</code></pre>
Example 106
   ```
aaa
  ```
<pre><code>aaa
</code></pre>

This is not a closing fence, because it is indented 4 spaces:

Example 107
```
aaa
    ```
<pre><code>aaa
    ```
</code></pre>

Code fences (opening and closing) cannot contain internal spaces:

Example 108
``` ```
aaa
<p><code> </code>
aaa</p>
Example 109
~~~~~~
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 110
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 111
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. Although this spec doesn't mandate any particular treatment of the info string, the first word is typically used to specify the language of the code block. In HTML output, the language is normally indicated by adding a class to the code element consisting of language- followed by the language name.

Example 112
```ruby
def foo(x)
  return 3
end
```
<pre><code class="language-ruby">def foo(x)
  return 3
end
</code></pre>
Example 113
~~~~    ruby startline=3 $%@#$
def foo(x)
  return 3
end
~~~~~~~
<pre><code class="language-ruby">def foo(x)
  return 3
end
</code></pre>
Example 114
````;
````
<pre><code class="language-;"></code></pre>

[Info strings] for backtick code blocks cannot contain backticks:

Example 115
``` aa ```
foo
<p><code>aa</code>
foo</p>

[Info strings] for tilde code blocks can contain backticks and tildes:

Example 116
~~~ aa ``` ~~~
foo
~~~
<pre><code class="language-aa">foo
</code></pre>

Closing code fences cannot have [info strings]:

Example 117
```
``` 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 the last line of the container block containing the current HTML 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, nav, noframes, ol, optgroup, option, p, param, section, 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] (with any [tag name] other than script, style, or pre) or a complete [closing tag], followed only by [whitespace] or the end of the line.
    End condition: line is followed by a [blank line].

HTML blocks continue until they are closed by their appropriate [end condition], or the last line of the document or other container block. This means any HTML within an HTML block that might otherwise be recognised as a start condition will be ignored by the parser and passed through as-is, without changing the parser's state.

For instance, <pre> within a HTML block started by <table> will not affect the parser state; as the HTML block was started in by start condition 6, it will end at any blank line. This can be surprising:

Example 118
<table><tr><td>
<pre>
**Hello**,

_world_.
</pre>
</td></tr></table>
<table><tr><td>
<pre>
**Hello**,
<p><em>world</em>.
</pre></p>
</td></tr></table>

In this case, the HTML block is terminated by the newline — the **Hello** text remains verbatim — and regular parsing resumes, with a paragraph, emphasised world and inline and block HTML following.

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 119
<table>
  <tr>
    <td>
           hi
    </td>
  </tr>
</table>

okay.
<table>
  <tr>
    <td>
           hi
    </td>
  </tr>
</table>
<p>okay.</p>
Example 120
 <div>
  *hello*
         <foo><a>
 <div>
  *hello*
         <foo><a>

A block can also start with a closing tag:

Example 121
</div>
*foo*
</div>
*foo*

Here we have two HTML blocks with a Markdown paragraph between them:

Example 122
<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 123
<div id="foo"
  class="bar">
</div>
<div id="foo"
  class="bar">
</div>
Example 124
<div id="foo" class="bar
  baz">
</div>
<div id="foo" class="bar
  baz">
</div>

An open tag need not be closed:

Example 125
<div>
*foo*

*bar*
<div>
*foo*
<p><em>bar</em></p>

A partial tag need not even be completed (garbage in, garbage out):

Example 126
<div id="foo"
*hi*
<div id="foo"
*hi*
Example 127
<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 128
<div *???-&&&-<---
*foo*
<div *???-&&&-<---
*foo*

In type 6 blocks, the initial tag need not be on a line by itself:

Example 129
<div><a href="bar">*foo*</a></div>
<div><a href="bar">*foo*</a></div>
Example 130
<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 131
<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 132
<a href="foo">
*bar*
</a>
<a href="foo">
*bar*
</a>

In type 7 blocks, the [tag name] can be anything:

Example 133
<Warning>
*bar*
</Warning>
<Warning>
*bar*
</Warning>
Example 134
<i class="foo">
*bar*
</i>
<i class="foo">
*bar*
</i>
Example 135
</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 136
<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 137
<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 138
<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 139
<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 140
<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 141
<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 142
<style
  type="text/css">

foo
<style
  type="text/css">

foo
Example 143
> <div>
> foo

bar
<blockquote>
<div>
foo
</blockquote>
<p>bar</p>
Example 144
- <div>
- foo
<ul>
<li>
<div>
</li>
<li>foo</li>
</ul>

The end tag can occur on the same line as the start tag:

Example 145
<style>p{color:red;}</style>
*foo*
<style>p{color:red;}</style>
<p><em>foo</em></p>
Example 146
<!-- 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 147
<script>
foo
</script>1. *bar*
<script>
foo
</script>1. *bar*

A comment (type 2):

Example 148
<!-- Foo

bar
   baz -->
okay
<!-- Foo

bar
   baz -->
<p>okay</p>

A processing instruction (type 3):

Example 149
<?php

  echo '>';

?>
okay
<?php

  echo '>';

?>
<p>okay</p>

A declaration (type 4):

Example 150
<!DOCTYPE html>
<!DOCTYPE html>

CDATA (type 5):

Example 151
<![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 152
  <!-- foo -->

    <!-- foo -->
  <!-- foo -->
<pre><code>&lt;!-- foo --&gt;
</code></pre>
Example 153
  <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 154
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][HTML block]:

Example 155
<div>
bar
</div>
*foo*
<div>
bar
</div>
*foo*

HTML blocks of type 7 cannot interrupt a paragraph:

Example 156
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:

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 157
<div>

*Emphasized* text.

</div>
<div>
<p><em>Emphasized</em> text.</p>
</div>
Example 158
<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 159
<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 160
<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][HTML blocks], 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 161
[foo]: /url "title"

[foo]
<p><a href="/url" title="title">foo</a></p>
Example 162
   [foo]: 
      /url  
           'the title'  

[foo]
<p><a href="/url" title="the title">foo</a></p>
Example 163
[Foo*bar\]]:my_(url) 'title (with parens)'

[Foo*bar\]]
<p><a href="my_(url)" title="title (with parens)">Foo*bar]</a></p>
Example 164
[Foo bar]:
<my url>
'title'

[Foo bar]
<p><a href="my%20url" title="title">Foo bar</a></p>

The title may extend over multiple lines:

Example 165
[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 166
[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 167
[foo]:
/url

[foo]
<p><a href="/url">foo</a></p>

The link destination may not be omitted:

Example 168
[foo]:

[foo]
<p>[foo]:</p>
<p>[foo]</p>

However, an empty link destination may be specified using angle brackets:

Example 169
[foo]: <>

[foo]
<p><a href="">foo</a></p>

The title must be separated from the link destination by whitespace:

Example 170
[foo]: <bar>(baz)

[foo]
<p>[foo]: <bar>(baz)</p>
<p>[foo]</p>

Both title and destination can contain backslash escapes and literal backslashes:

Example 171
[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 172
[foo]

[foo]: url
<p><a href="url">foo</a></p>

If there are several matching definitions, the first one takes precedence:

Example 173
[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 174
[FOO]: /url

[Foo]
<p><a href="/url">Foo</a></p>
Example 175
[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 176
[foo]: /url

Here is another one:

Example 177
[
foo
]: /url
bar
<p>bar</p>

This is not a link reference definition, because there are [non-whitespace characters] after the title:

Example 178
[foo]: /url "title" ok
<p>[foo]: /url &quot;title&quot; ok</p>

This is a link reference definition, but it has no title:

Example 179
[foo]: /url
"title" ok
<p>&quot;title&quot; ok</p>

This is not a link reference definition, because it is indented four spaces:

Example 180
    [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 181
```
[foo]: /url
```

[foo]
<pre><code>[foo]: /url
</code></pre>
<p>[foo]</p>

A [link reference definition] cannot interrupt a paragraph.

Example 182
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 183
# [Foo]
[foo]: /url
> bar
<h1><a href="/url">Foo</a></h1>
<blockquote>
<p>bar</p>
</blockquote>
Example 184
[foo]: /url
bar
===
[foo]
<h1>bar</h1>
<p><a href="/url">foo</a></p>
Example 185
[foo]: /url
===
[foo]
<p>===
<a href="/url">foo</a></p>

Several [link reference definitions] can occur one after another, without intervening blank lines.

Example 186
[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 187
[foo]

> [foo]: /url
<p><a href="/url">foo</a></p>
<blockquote>
</blockquote>

Whether something is a [link reference definition] is independent of whether the link reference it defines is used in the document. Thus, for example, the following document contains just a link reference definition, and no visible content:

Example 188
[foo]: /url

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 189
aaa

bbb
<p>aaa</p>
<p>bbb</p>

Paragraphs can contain multiple lines, but no blank lines:

Example 190
aaa
bbb

ccc
ddd
<p>aaa
bbb</p>
<p>ccc
ddd</p>

Multiple blank lines between paragraph have no effect:

Example 191
aaa


bbb
<p>aaa</p>
<p>bbb</p>

Leading spaces are skipped:

Example 192
  aaa
 bbb
<p>aaa
bbb</p>

Lines after the first may be indented any amount, since indented code blocks cannot interrupt paragraphs.

Example 193
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 194
   aaa
bbb
<p>aaa
bbb</p>
Example 195
    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 196
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 197
  

aaa
  

# aaa

  
<p>aaa</p>
<h1>aaa</h1>

Tables (extension)

GFM enables the table extension, where an additional leaf block type is available.

A table is an arrangement of data with rows and columns, consisting of a single header row, a [delimiter row] separating the header from the data, and zero or more data rows.

Each row consists of cells containing arbitrary text, in which [inlines] are parsed, separated by pipes (|). A leading and trailing pipe is also recommended for clarity of reading, and if there's otherwise parsing ambiguity. Spaces between pipes and cell content are trimmed. Block-level elements cannot be inserted in a table.

The delimiter row consists of cells whose only content are hyphens (-), and optionally, a leading or trailing colon (:), or both, to indicate left, right, or center alignment respectively.

Example 198
| foo | bar |
| --- | --- |
| baz | bim |
<table>
<thead>
<tr>
<th>foo</th>
<th>bar</th>
</tr>
</thead>
<tbody>
<tr>
<td>baz</td>
<td>bim</td>
</tr>
</tbody>
</table>

Cells in one column don't need to match length, though it's easier to read if they are. Likewise, use of leading and trailing pipes may be inconsistent:

Example 199
| abc | defghi |
:-: | -----------:
bar | baz
<table>
<thead>
<tr>
<th align="center">abc</th>
<th align="right">defghi</th>
</tr>
</thead>
<tbody>
<tr>
<td align="center">bar</td>
<td align="right">baz</td>
</tr>
</tbody>
</table>

Include a pipe in a cell's content by escaping it, including inside other inline spans:

Example 200
| f\|oo  |
| ------ |
| b `\|` az |
| b **\|** im |
<table>
<thead>
<tr>
<th>f|oo</th>
</tr>
</thead>
<tbody>
<tr>
<td>b <code>|</code> az</td>
</tr>
<tr>
<td>b <strong>|</strong> im</td>
</tr>
</tbody>
</table>

The table is broken at the first empty line, or beginning of another block-level structure:

Example 201
| abc | def |
| --- | --- |
| bar | baz |
> bar
<table>
<thead>
<tr>
<th>abc</th>
<th>def</th>
</tr>
</thead>
<tbody>
<tr>
<td>bar</td>
<td>baz</td>
</tr>
</tbody>
</table>
<blockquote>
<p>bar</p>
</blockquote>
Example 202
| abc | def |
| --- | --- |
| bar | baz |
bar

bar
<table>
<thead>
<tr>
<th>abc</th>
<th>def</th>
</tr>
</thead>
<tbody>
<tr>
<td>bar</td>
<td>baz</td>
</tr>
<tr>
<td>bar</td>
<td></td>
</tr>
</tbody>
</table>
<p>bar</p>

The header row must match the [delimiter row] in the number of cells. If not, a table will not be recognized:

Example 203
| abc | def |
| --- |
| bar |
<p>| abc | def |
| --- |
| bar |</p>

The remainder of the table's rows may vary in the number of cells. If there are a number of cells fewer than the number of cells in the header row, empty cells are inserted. If there are greater, the excess is ignored:

Example 204
| abc | def |
| --- | --- |
| bar |
| bar | baz | boo |
<table>
<thead>
<tr>
<th>abc</th>
<th>def</th>
</tr>
</thead>
<tbody>
<tr>
<td>bar</td>
<td></td>
</tr>
<tr>
<td>bar</td>
<td>baz</td>
</tr>
</tbody>
</table>

If there are no rows in the body, no <tbody> is generated in HTML output:

Example 205
| abc | def |
| --- | --- |
<table>
<thead>
<tr>
<th>abc</th>
<th>def</th>
</tr>
</thead>
</table>

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.)

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 containing Bs.

  2. Laziness. If a string of lines Ls constitute a block quote 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.

Here is a simple example:

Example 206
> # Foo
> bar
> baz
<blockquote>
<h1>Foo</h1>
<p>bar
baz</p>
</blockquote>

The spaces after the > characters can be omitted:

Example 207
># Foo
>bar
> baz
<blockquote>
<h1>Foo</h1>
<p>bar
baz</p>
</blockquote>

The > characters can be indented 1-3 spaces:

Example 208
   > # Foo
   > bar
 > baz
<blockquote>
<h1>Foo</h1>
<p>bar
baz</p>
</blockquote>

Four spaces gives us a code block:

Example 209
    > # 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 210
> # 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 211
> 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

> foo
> ---

without changing the meaning:

Example 212
> foo
---
<blockquote>
<p>foo</p>
</blockquote>
<hr />

Similarly, if we omit the > in the second line of

> - foo
> - bar

then the block quote ends after the first line:

Example 213
> - 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 214
>     foo
    bar
<blockquote>
<pre><code>foo
</code></pre>
</blockquote>
<pre><code>bar
</code></pre>
Example 215
> ```
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 216
> foo
    - bar
<blockquote>
<p>foo
- bar</p>
</blockquote>

To see why, note that in

> 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 217
>
<blockquote>
</blockquote>
Example 218
>
>  
> 
<blockquote>
</blockquote>

A block quote can have initial or final blank lines:

Example 219
>
> foo
>  
<blockquote>
<p>foo</p>
</blockquote>

A blank line always separates block quotes:

Example 220
> 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 221
> foo
> bar
<blockquote>
<p>foo
bar</p>
</blockquote>

To get a block quote with two paragraphs, use:

Example 222
> foo
>
> bar
<blockquote>
<p>foo</p>
<p>bar</p>
</blockquote>

Block quotes can interrupt paragraphs:

Example 223
foo
> bar
<p>foo</p>
<blockquote>
<p>bar</p>
</blockquote>

In general, blank lines are not needed before or after block quotes:

Example 224
> 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 225
> bar
baz
<blockquote>
<p>bar
baz</p>
</blockquote>
Example 226
> bar

baz
<blockquote>
<p>bar</p>
</blockquote>
<p>baz</p>
Example 227
> 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 228
> > > foo
bar
<blockquote>
<blockquote>
<blockquote>
<p>foo
bar</p>
</blockquote>
</blockquote>
</blockquote>
Example 229
>>> 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 230
>     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 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:

    1. 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.
    2. If any line is a [thematic break][thematic breaks] then that line is not a list item.

For example, let Ls be the lines

Example 231
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 232
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 233
- one

 two
<ul>
<li>one</li>
</ul>
<p>two</p>
Example 234
- one

  two
<ul>
<li>
<p>one</p>
<p>two</p>
</li>
</ul>
Example 235
 -    one

     two
<ul>
<li>one</li>
</ul>
<pre><code> two
</code></pre>
Example 236
 -    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 237
   > > 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 238
>>- 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 239
-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 240
- foo


  bar
<ul>
<li>
<p>foo</p>
<p>bar</p>
</li>
</ul>

A list item may contain any kind of block:

Example 241
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 242
- 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 243
123456789. ok
<ol start="123456789">
<li>ok</li>
</ol>
Example 244
1234567890. not ok
<p>1234567890. not ok</p>

A start number may begin with 0s:

Example 245
0. ok
<ol start="0">
<li>ok</li>
</ol>
Example 246
003. ok
<ol start="3">
<li>ok</li>
</ol>

A start number may not be negative:

Example 247
-1. not ok
<p>-1. not ok</p>
  1. Item starting with indented code. If a sequence of lines Ls constitute a sequence of blocks Bs starting with an indented code block, 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 248
- foo

      bar
<ul>
<li>
<p>foo</p>
<pre><code>bar
</code></pre>
</li>
</ul>

And in this case it is 11 spaces:

Example 249
  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 250
    indented code

paragraph

    more code
<pre><code>indented code
</code></pre>
<p>paragraph</p>
<pre><code>more code
</code></pre>
Example 251
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 252
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 253
   foo

bar
<p>foo</p>
<p>bar</p>
Example 254
-    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 255
-  foo

   bar
<ul>
<li>
<p>foo</p>
<p>bar</p>
</li>
</ul>
  1. 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 256
-
  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 257
-   
  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 258
-

  foo
<ul>
<li></li>
</ul>
<p>foo</p>

Here is an empty bullet list item:

Example 259
- 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 260
- foo
-   
- bar
<ul>
<li>foo</li>
<li></li>
<li>bar</li>
</ul>

Here is an empty ordered list item:

Example 261
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 262
*
<ul>
<li></li>
</ul>

However, an empty list item cannot interrupt a paragraph:

Example 263
foo
*

foo
1.
<p>foo
*</p>
<p>foo
1.</p>
  1. 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 264
 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 265
  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 266
   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 267
    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>
  1. Laziness. If a string of lines Ls constitute a list item 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 lines.

Here is an example with [lazy continuation lines]:

Example 268
  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 269
  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 270
> 1. > Blockquote
continued here.
<blockquote>
<ol>
<li>
<blockquote>
<p>Blockquote
continued here.</p>
</blockquote>
</li>
</ol>
</blockquote>
Example 271
> 1. > Blockquote
> continued here.
<blockquote>
<ol>
<li>
<blockquote>
<p>Blockquote
continued here.</p>
</blockquote>
</li>
</ol>
</blockquote>
  1. That's all. Nothing that is not counted as a list item by rules #1--5 counts as a list item.

The rules for sublists follow from the general rules [above][List items]. 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 272
- 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 273
- 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 274
10) foo
    - bar
<ol start="10">
<li>foo
<ul>
<li>bar</li>
</ul>
</li>
</ol>

Three is not enough:

Example 275
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 276
- - foo
<ul>
<li>
<ul>
<li>foo</li>
</ul>
</li>
</ul>
Example 277
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 278
- # 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

- foo

  bar

  - baz

should be parsed as two lists with an intervening paragraph,

<ul>
<li>foo</li>
</ul>
<p>bar</p>
<ul>
<li>baz</li>
</ul>

as the four-space rule demands, rather than a single list,

<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

   - one

  two

as a single list item, with two a continuation paragraph:

<ul>
<li>
<p>one</p>
<p>two</p>
</li>
</ul>

and similarly

>   - one
>
>  two

as

<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:

 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:

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.

Task list items (extension)

GFM enables the tasklist extension, where an additional processing step is performed on [list items].

A task list item is a [list item][list items] where the first block in it is a paragraph which begins with a [task list item marker] and at least one whitespace character before any other content.

A task list item marker consists of an optional number of spaces, a left bracket ([), either a whitespace character or the letter x in either lowercase or uppercase, and then a right bracket (]).

When rendered, the [task list item marker] is replaced with a semantic checkbox element; in an HTML output, this would be an <input type="checkbox"> element.

If the character between the brackets is a whitespace character, the checkbox is unchecked. Otherwise, the checkbox is checked.

This spec does not define how the checkbox elements are interacted with: in practice, implementors are free to render the checkboxes as disabled or inmutable elements, or they may dynamically handle dynamic interactions (i.e. checking, unchecking) in the final rendered document.

Example 279
- [ ] foo
- [x] bar
<ul>
<li><input disabled="" type="checkbox"> foo</li>
<li><input checked="" disabled="" type="checkbox"> bar</li>
</ul>

Task lists can be arbitrarily nested:

Example 280
- [x] foo
  - [ ] bar
  - [x] baz
- [ ] bim
<ul>
<li><input checked="" disabled="" type="checkbox"> foo
<ul>
<li><input disabled="" type="checkbox"> bar</li>
<li><input checked="" disabled="" type="checkbox"> baz</li>
</ul>
</li>
<li><input disabled="" type="checkbox"> bim</li>
</ul>

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 281
- foo
- bar
+ baz
<ul>
<li>foo</li>
<li>bar</li>
</ul>
<ul>
<li>baz</li>
</ul>
Example 282
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 283
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:

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:

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

  * 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

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 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 284
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 285
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 286
- foo

- bar


- baz
<ul>
<li>
<p>foo</p>
</li>
<li>
<p>bar</p>
</li>
<li>
<p>baz</p>
</li>
</ul>
Example 287
- foo
  - bar
    - baz


      bim
<ul>
<li>foo
<ul>
<li>bar
<ul>
<li>
<p>baz</p>
<p>bim</p>
</li>
</ul>
</li>
</ul>
</li>
</ul>

To separate consecutive lists of the same type, or to separate a list from an indented code block that would otherwise be parsed as a subparagraph of the final list item, you can insert a blank HTML comment:

Example 288
- foo
- bar

<!-- -->

- baz
- bim
<ul>
<li>foo</li>
<li>bar</li>
</ul>
<!-- -->
<ul>
<li>baz</li>
<li>bim</li>
</ul>
Example 289
-   foo

    notcode

-   foo

<!-- -->

    code
<ul>
<li>
<p>foo</p>
<p>notcode</p>
</li>
<li>
<p>foo</p>
</li>
</ul>
<!-- -->
<pre><code>code
</code></pre>

List items need not be indented to the same level. The following list items will be treated as items at the same list level, since none is indented enough to belong to the previous list item:

Example 290
- a
 - b
  - c
   - d
  - e
 - f
- g
<ul>
<li>a</li>
<li>b</li>
<li>c</li>
<li>d</li>
<li>e</li>
<li>f</li>
<li>g</li>
</ul>
Example 291
1. a

  2. b

   3. c
<ol>
<li>
<p>a</p>
</li>
<li>
<p>b</p>
</li>
<li>
<p>c</p>
</li>
</ol>

Note, however, that list items may not be indented more than three spaces. Here - e is treated as a paragraph continuation line, because it is indented more than three spaces:

Example 292
- a
 - b
  - c
   - d
    - e
<ul>
<li>a</li>
<li>b</li>
<li>c</li>
<li>d
- e</li>
</ul>

And here, 3. c is treated as in indented code block, because it is indented four spaces and preceded by a blank line.

Example 293
1. a

  2. b

    3. c
<ol>
<li>
<p>a</p>
</li>
<li>
<p>b</p>
</li>
</ol>
<pre><code>3. c
</code></pre>

This is a loose list, because there is a blank line between two of the list items:

Example 294
- a
- b

- c
<ul>
<li>
<p>a</p>
</li>
<li>
<p>b</p>
</li>
<li>
<p>c</p>
</li>
</ul>

So is this, with a empty second item:

Example 295
* a
*

* c
<ul>
<li>
<p>a</p>
</li>
<li></li>
<li>
<p>c</p>
</li>
</ul>

These are loose lists, even though there is no space between the items, because one of the items directly contains two block-level elements with a blank line between them:

Example 296
- a
- b

  c
- d
<ul>
<li>
<p>a</p>
</li>
<li>
<p>b</p>
<p>c</p>
</li>
<li>
<p>d</p>
</li>
</ul>
Example 297
- a
- b

  [ref]: /url
- d
<ul>
<li>
<p>a</p>
</li>
<li>
<p>b</p>
</li>
<li>
<p>d</p>
</li>
</ul>

This is a tight list, because the blank lines are in a code block:

Example 298
- a
- ```
  b


  ```
- c
<ul>
<li>a</li>
<li>
<pre><code>b


</code></pre>
</li>
<li>c</li>
</ul>

This is a tight list, because the blank line is between two paragraphs of a sublist. So the sublist is loose while the outer list is tight:

Example 299
- a
  - b

    c
- d
<ul>
<li>a
<ul>
<li>
<p>b</p>
<p>c</p>
</li>
</ul>
</li>
<li>d</li>
</ul>

This is a tight list, because the blank line is inside the block quote:

Example 300
* a
  > b
  >
* c
<ul>
<li>a
<blockquote>
<p>b</p>
</blockquote>
</li>
<li>c</li>
</ul>

This list is tight, because the consecutive block elements are not separated by blank lines:

Example 301
- a
  > b
  ```
  c
  ```
- d
<ul>
<li>a
<blockquote>
<p>b</p>
</blockquote>
<pre><code>c
</code></pre>
</li>
<li>d</li>
</ul>

A single-paragraph list is tight:

Example 302
- a
<ul>
<li>a</li>
</ul>
Example 303
- a
  - b
<ul>
<li>a
<ul>
<li>b</li>
</ul>
</li>
</ul>

This list is loose, because of the blank line between the two block elements in the list item:

Example 304
1. ```
   foo
   ```

   bar
<ol>
<li>
<pre><code>foo
</code></pre>
<p>bar</p>
</li>
</ol>

Here the outer list is loose, the inner list tight:

Example 305
* foo
  * bar

  baz
<ul>
<li>
<p>foo</p>
<ul>
<li>bar</li>
</ul>
<p>baz</p>
</li>
</ul>
Example 306
- a
  - b
  - c

- d
  - e
  - f
<ul>
<li>
<p>a</p>
<ul>
<li>b</li>
<li>c</li>
</ul>
</li>
<li>
<p>d</p>
<ul>
<li>e</li>
<li>f</li>
</ul>
</li>
</ul>

Inlines

Inlines are parsed sequentially from the beginning of the character stream to the end (left to right, in left-to-right languages). Thus, for example, in

Example 307
`hi`lo`
<p><code>hi</code>lo`</p>

hi is parsed as code, leaving the backtick at the end as a literal backtick.

Backslash escapes

Any ASCII punctuation character may be backslash-escaped:

Example 308
\!\"\#\$\%\&\'\(\)\*\+\,\-\.\/\:\;\<\=\>\?\@\[\\\]\^\_\`\{\|\}\~
<p>!&quot;#$%&amp;'()*+,-./:;&lt;=&gt;?@[\]^_`{|}~</p>

Backslashes before other characters are treated as literal backslashes:

Example 309
\→\A\a\ \3\φ\«
<p>\→\A\a\ \3\φ\«</p>

Escaped characters are treated as regular characters and do not have their usual Markdown meanings:

Example 310
\*not emphasized*
\<br/> not a tag
\[not a link](/foo)
\`not code`
1\. not a list
\* not a list
\# not a heading
\[foo]: /url "not a reference"
\ö not a character entity
<p>*not emphasized*
&lt;br/&gt; not a tag
[not a link](/foo)
`not code`
1. not a list
* not a list
# not a heading
[foo]: /url &quot;not a reference&quot;
&amp;ouml; not a character entity</p>

If a backslash is itself escaped, the following character is not:

Example 311
\\*emphasis*
<p>\<em>emphasis</em></p>

A backslash at the end of the line is a [hard line break]:

Example 312
foo\
bar
<p>foo<br />
bar</p>

Backslash escapes do not work in code blocks, code spans, autolinks, or raw HTML:

Example 313
`` \[\` ``
<p><code>\[\`</code></p>
Example 314
    \[\]
<pre><code>\[\]
</code></pre>
Example 315
~~~
\[\]
~~~
<pre><code>\[\]
</code></pre>
Example 316
<http://example.com?find=\*>
<p><a href="http://example.com?find=%5C*">http://example.com?find=\*</a></p>
Example 317
<a href="/bar\/)">
<a href="/bar\/)">

But they work in all other contexts, including URLs and link titles, link references, and [info strings] in [fenced code blocks]:

Example 318
[foo](/bar\* "ti\*tle")
<p><a href="/bar*" title="ti*tle">foo</a></p>
Example 319
[foo]

[foo]: /bar\* "ti\*tle"
<p><a href="/bar*" title="ti*tle">foo</a></p>
Example 320
``` foo\+bar
foo
```
<pre><code class="language-foo+bar">foo
</code></pre>

Entity and numeric character references

Valid HTML entity references and numeric character references can be used in place of the corresponding Unicode character, with the following exceptions:

Conforming CommonMark parsers need not store information about whether a particular character was represented in the source using a Unicode character or an entity reference.

Entity references consist of & + any of the valid HTML5 entity names + ;. The document https://html.spec.whatwg.org/multipage/entities.json is used as an authoritative source for the valid entity references and their corresponding code points.

Example 321
&nbsp; &amp; &copy; &AElig; &Dcaron;
&frac34; &HilbertSpace; &DifferentialD;
&ClockwiseContourIntegral; &ngE;
<p>  &amp; © Æ Ď
¾ ℋ ⅆ
∲ ≧̸</p>

Decimal numeric character references consist of &# + a string of 1--7 arabic digits + ;. A numeric character reference is parsed as the corresponding Unicode character. Invalid Unicode code points will be replaced by the REPLACEMENT CHARACTER (U+FFFD). For security reasons, the code point U+0000 will also be replaced by U+FFFD.

Example 322
&#35; &#1234; &#992; &#0;
<p># Ӓ Ϡ �</p>

Hexadecimal numeric character references consist of &# + either X or x + a string of 1-6 hexadecimal digits + ;. They too are parsed as the corresponding Unicode character (this time specified with a hexadecimal numeral instead of decimal).

Example 323
&#X22; &#XD06; &#xcab;
<p>&quot; ആ ಫ</p>

Here are some nonentities:

Example 324
&nbsp &x; &#; &#x;
&#987654321;
&#abcdef0;
&ThisIsNotDefined; &hi?;
<p>&amp;nbsp &amp;x; &amp;#; &amp;#x;
&amp;#987654321;
&amp;#abcdef0;
&amp;ThisIsNotDefined; &amp;hi?;</p>

Although HTML5 does accept some entity references without a trailing semicolon (such as &copy), these are not recognized here, because it makes the grammar too ambiguous:

Example 325
&copy
<p>&amp;copy</p>

Strings that are not on the list of HTML5 named entities are not recognized as entity references either:

Example 326
&MadeUpEntity;
<p>&amp;MadeUpEntity;</p>

Entity and numeric character references are recognized in any context besides code spans or code blocks, including URLs, [link titles], and [fenced code block][] [info strings]:

Example 327
<a href="&ouml;&ouml;.html">
<a href="&ouml;&ouml;.html">
Example 328
[foo](/f&ouml;&ouml; "f&ouml;&ouml;")
<p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p>
Example 329
[foo]

[foo]: /f&ouml;&ouml; "f&ouml;&ouml;"
<p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p>
Example 330
``` f&ouml;&ouml;
foo
```
<pre><code class="language-föö">foo
</code></pre>

Entity and numeric character references are treated as literal text in code spans and code blocks:

Example 331
`f&ouml;&ouml;`
<p><code>f&amp;ouml;&amp;ouml;</code></p>
Example 332
    f&ouml;f&ouml;
<pre><code>f&amp;ouml;f&amp;ouml;
</code></pre>

Entity and numeric character references cannot be used in place of symbols indicating structure in CommonMark documents.

Example 333
&#42;foo&#42;
*foo*
<p>*foo*
<em>foo</em></p>
Example 334
&#42; foo

* foo
<p>* foo</p>
<ul>
<li>foo</li>
</ul>
Example 335
foo&#10;&#10;bar
<p>foo

bar</p>
Example 336
&#9;foo
<p>→foo</p>
Example 337
[a](url &quot;tit&quot;)
<p>[a](url &quot;tit&quot;)</p>

Code spans

A backtick string is a string of one or more backtick characters (`) that is neither preceded nor followed by a backtick.

A code span begins with a backtick string and ends with a backtick string of equal length. The contents of the code span are the characters between the two backtick strings, normalized in the following ways:

This is a simple code span:

Example 338
`foo`
<p><code>foo</code></p>

Here two backticks are used, because the code contains a backtick. This example also illustrates stripping of a single leading and trailing space:

Example 339
`` foo ` bar ``
<p><code>foo ` bar</code></p>

This example shows the motivation for stripping leading and trailing spaces:

Example 340
` `` `
<p><code>``</code></p>

Note that only one space is stripped:

Example 341
`  ``  `
<p><code> `` </code></p>

The stripping only happens if the space is on both sides of the string:

Example 342
` a`
<p><code> a</code></p>

Only [spaces], and not [unicode whitespace] in general, are stripped in this way:

Example 343
` b `
<p><code> b </code></p>

No stripping occurs if the code span contains only spaces:

Example 344
` `
`  `
<p><code> </code>
<code>  </code></p>

[Line endings] are treated like spaces:

Example 345
``
foo
bar  
baz
``
<p><code>foo bar   baz</code></p>
Example 346
``
foo 
``
<p><code>foo </code></p>

Interior spaces are not collapsed:

Example 347
`foo   bar 
baz`
<p><code>foo   bar  baz</code></p>

Note that browsers will typically collapse consecutive spaces when rendering <code> elements, so it is recommended that the following CSS be used:

code{white-space: pre-wrap;}

Note that backslash escapes do not work in code spans. All backslashes are treated literally:

Example 348
`foo\`bar`
<p><code>foo\</code>bar`</p>

Backslash escapes are never needed, because one can always choose a string of n backtick characters as delimiters, where the code does not contain any strings of exactly n backtick characters.

Example 349
``foo`bar``
<p><code>foo`bar</code></p>
Example 350
` foo `` bar `
<p><code>foo `` bar</code></p>

Code span backticks have higher precedence than any other inline constructs except HTML tags and autolinks. Thus, for example, this is not parsed as emphasized text, since the second * is part of a code span:

Example 351
*foo`*`
<p>*foo<code>*</code></p>

And this is not parsed as a link:

Example 352
[not a `link](/foo`)
<p>[not a <code>link](/foo</code>)</p>

Code spans, HTML tags, and autolinks have the same precedence. Thus, this is code:

Example 353
`<a href="`">`
<p><code>&lt;a href=&quot;</code>&quot;&gt;`</p>

But this is an HTML tag:

Example 354
<a href="`">`
<p><a href="`">`</p>

And this is code:

Example 355
`<http://foo.bar.`baz>`
<p><code>&lt;http://foo.bar.</code>baz&gt;`</p>

But this is an autolink:

Example 356
<http://foo.bar.`baz>`
<p><a href="http://foo.bar.%60baz">http://foo.bar.`baz</a>`</p>

When a backtick string is not closed by a matching backtick string, we just have literal backticks:

Example 357
```foo``
<p>```foo``</p>
Example 358
`foo
<p>`foo</p>

The following case also illustrates the need for opening and closing backtick strings to be equal in length:

Example 359
`foo``bar``
<p>`foo<code>bar</code></p>

Emphasis and strong emphasis

John Gruber's original Markdown syntax description says:

Markdown treats asterisks (*) and underscores (_) as indicators of emphasis. Text wrapped with one * or _ will be wrapped with an HTML <em> tag; double *'s or _'s will be wrapped with an HTML <strong> tag.

This is enough for most users, but these rules leave much undecided, especially when it comes to nested emphasis. The original Markdown.pl test suite makes it clear that triple *** and ___ delimiters can be used for strong emphasis, and most implementations have also allowed the following patterns:

***strong emph***
***strong** in emph*
***emph* in strong**
**in strong *emph***
*in emph **strong***

The following patterns are less widely supported, but the intent is clear and they are useful (especially in contexts like bibliography entries):

*emph *with emph* in it*
**strong **with strong** in it**

Many implementations have also restricted intraword emphasis to the * forms, to avoid unwanted emphasis in words containing internal underscores. (It is best practice to put these in code spans, but users often do not.)

internal emphasis: foo*bar*baz
no emphasis: foo_bar_baz

The rules given below capture all of these patterns, while allowing for efficient parsing strategies that do not backtrack.

First, some definitions. A delimiter run is either a sequence of one or more * characters that is not preceded or followed by a non-backslash-escaped * character, or a sequence of one or more _ characters that is not preceded or followed by a non-backslash-escaped _ character.

A left-flanking delimiter run is a [delimiter run] that is (1) not followed by [Unicode whitespace], and either (2a) not followed by a [punctuation character], or (2b) followed by a [punctuation character] and preceded by [Unicode whitespace] or a [punctuation character]. For purposes of this definition, the beginning and the end of the line count as Unicode whitespace.

A right-flanking delimiter run is a [delimiter run] that is (1) not preceded by [Unicode whitespace], and either (2a) not preceded by a [punctuation character], or (2b) preceded by a [punctuation character] and followed by [Unicode whitespace] or a [punctuation character]. For purposes of this definition, the beginning and the end of the line count as Unicode whitespace.

Here are some examples of delimiter runs.

(The idea of distinguishing left-flanking and right-flanking delimiter runs based on the character before and the character after comes from Roopesh Chander's vfmd. vfmd uses the terminology "emphasis indicator string" instead of "delimiter run," and its rules for distinguishing left- and right-flanking runs are a bit more complex than the ones given here.)

The following rules define emphasis and strong emphasis:

  1. A single * character can open emphasis iff (if and only if) it is part of a [left-flanking delimiter run].

  2. A single _ character [can open emphasis] iff it is part of a [left-flanking delimiter run] and either (a) not part of a [right-flanking delimiter run] or (b) part of a [right-flanking delimiter run] preceded by punctuation.

  3. A single * character can close emphasis iff it is part of a [right-flanking delimiter run].

  4. A single _ character [can close emphasis] iff it is part of a [right-flanking delimiter run] and either (a) not part of a [left-flanking delimiter run] or (b) part of a [left-flanking delimiter run] followed by punctuation.

  5. A double ** can open strong emphasis iff it is part of a [left-flanking delimiter run].

  6. A double __ [can open strong emphasis] iff it is part of a [left-flanking delimiter run] and either (a) not part of a [right-flanking delimiter run] or (b) part of a [right-flanking delimiter run] preceded by punctuation.

  7. A double ** can close strong emphasis iff it is part of a [right-flanking delimiter run].

  8. A double __ [can close strong emphasis] iff it is part of a [right-flanking delimiter run] and either (a) not part of a [left-flanking delimiter run] or (b) part of a [left-flanking delimiter run] followed by punctuation.

  9. Emphasis begins with a delimiter that [can open emphasis] and ends with a delimiter that [can close emphasis], and that uses the same character (_ or *) as the opening delimiter. The opening and closing delimiters must belong to separate [delimiter runs]. If one of the delimiters can both open and close emphasis, then the sum of the lengths of the delimiter runs containing the opening and closing delimiters must not be a multiple of 3 unless both lengths are multiples of 3.

  10. Strong emphasis begins with a delimiter that [can open strong emphasis] and ends with a delimiter that [can close strong emphasis], and that uses the same character (_ or *) as the opening delimiter. The opening and closing delimiters must belong to separate [delimiter runs]. If one of the delimiters can both open and close strong emphasis, then the sum of the lengths of the delimiter runs containing the opening and closing delimiters must not be a multiple of 3 unless both lengths are multiples of 3.

  11. A literal * character cannot occur at the beginning or end of *-delimited emphasis or **-delimited strong emphasis, unless it is backslash-escaped.

  12. A literal _ character cannot occur at the beginning or end of _-delimited emphasis or __-delimited strong emphasis, unless it is backslash-escaped.

Where rules 1--12 above are compatible with multiple parsings, the following principles resolve ambiguity:

  1. The number of nestings should be minimized. Thus, for example, an interpretation <strong>...</strong> is always preferred to <em><em>...</em></em>.

  2. An interpretation <em><strong>...</strong></em> is always preferred to <strong><em>...</em></strong>.

  3. When two potential emphasis or strong emphasis spans overlap, so that the second begins before the first ends and ends after the first ends, the first takes precedence. Thus, for example, *foo _bar* baz_ is parsed as <em>foo _bar</em> baz_ rather than *foo <em>bar* baz</em>.

  4. When there are two potential emphasis or strong emphasis spans with the same closing delimiter, the shorter one (the one that opens later) takes precedence. Thus, for example, **foo **bar baz** is parsed as **foo <strong>bar baz</strong> rather than <strong>foo **bar baz</strong>.

  5. Inline code spans, links, images, and HTML tags group more tightly than emphasis. So, when there is a choice between an interpretation that contains one of these elements and one that does not, the former always wins. Thus, for example, *[foo*](bar) is parsed as *<a href="bar">foo*</a> rather than as <em>[foo</em>](bar).

These rules can be illustrated through a series of examples.

Rule 1:

Example 360
*foo bar*
<p><em>foo bar</em></p>

This is not emphasis, because the opening * is followed by whitespace, and hence not part of a [left-flanking delimiter run]:

Example 361
a * foo bar*
<p>a * foo bar*</p>

This is not emphasis, because the opening * is preceded by an alphanumeric and followed by punctuation, and hence not part of a [left-flanking delimiter run]:

Example 362
a*"foo"*
<p>a*&quot;foo&quot;*</p>

Unicode nonbreaking spaces count as whitespace, too:

Example 363
* a *
<p>* a *</p>

Intraword emphasis with * is permitted:

Example 364
foo*bar*
<p>foo<em>bar</em></p>
Example 365
5*6*78
<p>5<em>6</em>78</p>

Rule 2:

Example 366
_foo bar_
<p><em>foo bar</em></p>

This is not emphasis, because the opening _ is followed by whitespace:

Example 367
_ foo bar_
<p>_ foo bar_</p>

This is not emphasis, because the opening _ is preceded by an alphanumeric and followed by punctuation:

Example 368
a_"foo"_
<p>a_&quot;foo&quot;_</p>

Emphasis with _ is not allowed inside words:

Example 369
foo_bar_
<p>foo_bar_</p>
Example 370
5_6_78
<p>5_6_78</p>
Example 371
пристаням_стремятся_
<p>пристаням_стремятся_</p>

Here _ does not generate emphasis, because the first delimiter run is right-flanking and the second left-flanking:

Example 372
aa_"bb"_cc
<p>aa_&quot;bb&quot;_cc</p>

This is emphasis, even though the opening delimiter is both left- and right-flanking, because it is preceded by punctuation:

Example 373
foo-_(bar)_
<p>foo-<em>(bar)</em></p>

Rule 3:

This is not emphasis, because the closing delimiter does not match the opening delimiter:

Example 374
_foo*
<p>_foo*</p>

This is not emphasis, because the closing * is preceded by whitespace:

Example 375
*foo bar *
<p>*foo bar *</p>

A newline also counts as whitespace:

Example 376
*foo bar
*
<p>*foo bar
*</p>

This is not emphasis, because the second * is preceded by punctuation and followed by an alphanumeric (hence it is not part of a [right-flanking delimiter run]:

Example 377
*(*foo)
<p>*(*foo)</p>

The point of this restriction is more easily appreciated with this example:

Example 378
*(*foo*)*
<p><em>(<em>foo</em>)</em></p>

Intraword emphasis with * is allowed:

Example 379
*foo*bar
<p><em>foo</em>bar</p>

Rule 4:

This is not emphasis, because the closing _ is preceded by whitespace:

Example 380
_foo bar _
<p>_foo bar _</p>

This is not emphasis, because the second _ is preceded by punctuation and followed by an alphanumeric:

Example 381
_(_foo)
<p>_(_foo)</p>

This is emphasis within emphasis:

Example 382
_(_foo_)_
<p><em>(<em>foo</em>)</em></p>

Intraword emphasis is disallowed for _:

Example 383
_foo_bar
<p>_foo_bar</p>
Example 384
_пристаням_стремятся
<p>_пристаням_стремятся</p>
Example 385
_foo_bar_baz_
<p><em>foo_bar_baz</em></p>

This is emphasis, even though the closing delimiter is both left- and right-flanking, because it is followed by punctuation:

Example 386
_(bar)_.
<p><em>(bar)</em>.</p>

Rule 5:

Example 387
**foo bar**
<p><strong>foo bar</strong></p>

This is not strong emphasis, because the opening delimiter is followed by whitespace:

Example 388
** foo bar**
<p>** foo bar**</p>

This is not strong emphasis, because the opening ** is preceded by an alphanumeric and followed by punctuation, and hence not part of a [left-flanking delimiter run]:

Example 389
a**"foo"**
<p>a**&quot;foo&quot;**</p>

Intraword strong emphasis with ** is permitted:

Example 390
foo**bar**
<p>foo<strong>bar</strong></p>

Rule 6:

Example 391
__foo bar__
<p><strong>foo bar</strong></p>

This is not strong emphasis, because the opening delimiter is followed by whitespace:

Example 392
__ foo bar__
<p>__ foo bar__</p>

A newline counts as whitespace:

Example 393
__
foo bar__
<p>__
foo bar__</p>

This is not strong emphasis, because the opening __ is preceded by an alphanumeric and followed by punctuation:

Example 394
a__"foo"__
<p>a__&quot;foo&quot;__</p>

Intraword strong emphasis is forbidden with __:

Example 395
foo__bar__
<p>foo__bar__</p>
Example 396
5__6__78
<p>5__6__78</p>
Example 397
пристаням__стремятся__
<p>пристаням__стремятся__</p>
Example 398
__foo, __bar__, baz__
<p><strong>foo, <strong>bar</strong>, baz</strong></p>

This is strong emphasis, even though the opening delimiter is both left- and right-flanking, because it is preceded by punctuation:

Example 399
foo-__(bar)__
<p>foo-<strong>(bar)</strong></p>

Rule 7:

This is not strong emphasis, because the closing delimiter is preceded by whitespace:

Example 400
**foo bar **
<p>**foo bar **</p>

(Nor can it be interpreted as an emphasized *foo bar *, because of Rule 11.)

This is not strong emphasis, because the second ** is preceded by punctuation and followed by an alphanumeric:

Example 401
**(**foo)
<p>**(**foo)</p>

The point of this restriction is more easily appreciated with these examples:

Example 402
*(**foo**)*
<p><em>(<strong>foo</strong>)</em></p>
Example 403
**Gomphocarpus (*Gomphocarpus physocarpus*, syn.
*Asclepias physocarpa*)**
<p><strong>Gomphocarpus (<em>Gomphocarpus physocarpus</em>, syn.
<em>Asclepias physocarpa</em>)</strong></p>
Example 404
**foo "*bar*" foo**
<p><strong>foo &quot;<em>bar</em>&quot; foo</strong></p>

Intraword emphasis:

Example 405
**foo**bar
<p><strong>foo</strong>bar</p>

Rule 8:

This is not strong emphasis, because the closing delimiter is preceded by whitespace:

Example 406
__foo bar __
<p>__foo bar __</p>

This is not strong emphasis, because the second __ is preceded by punctuation and followed by an alphanumeric:

Example 407
__(__foo)
<p>__(__foo)</p>

The point of this restriction is more easily appreciated with this example:

Example 408
_(__foo__)_
<p><em>(<strong>foo</strong>)</em></p>

Intraword strong emphasis is forbidden with __:

Example 409
__foo__bar
<p>__foo__bar</p>
Example 410
__пристаням__стремятся
<p>__пристаням__стремятся</p>
Example 411
__foo__bar__baz__
<p><strong>foo__bar__baz</strong></p>

This is strong emphasis, even though the closing delimiter is both left- and right-flanking, because it is followed by punctuation:

Example 412
__(bar)__.
<p><strong>(bar)</strong>.</p>

Rule 9:

Any nonempty sequence of inline elements can be the contents of an emphasized span.

Example 413
*foo [bar](/url)*
<p><em>foo <a href="/url">bar</a></em></p>
Example 414
*foo
bar*
<p><em>foo
bar</em></p>

In particular, emphasis and strong emphasis can be nested inside emphasis:

Example 415
_foo __bar__ baz_
<p><em>foo <strong>bar</strong> baz</em></p>
Example 416
_foo _bar_ baz_
<p><em>foo <em>bar</em> baz</em></p>
Example 417
__foo_ bar_
<p><em><em>foo</em> bar</em></p>
Example 418
*foo *bar**
<p><em>foo <em>bar</em></em></p>
Example 419
*foo **bar** baz*
<p><em>foo <strong>bar</strong> baz</em></p>
Example 420
*foo**bar**baz*
<p><em>foo<strong>bar</strong>baz</em></p>

Note that in the preceding case, the interpretation

<p><em>foo</em><em>bar<em></em>baz</em></p>

is precluded by the condition that a delimiter that can both open and close (like the * after foo) cannot form emphasis if the sum of the lengths of the delimiter runs containing the opening and closing delimiters is a multiple of 3 unless both lengths are multiples of 3.

For the same reason, we don't get two consecutive emphasis sections in this example:

Example 421
*foo**bar*
<p><em>foo**bar</em></p>

The same condition ensures that the following cases are all strong emphasis nested inside emphasis, even when the interior spaces are omitted:

Example 422
***foo** bar*
<p><em><strong>foo</strong> bar</em></p>
Example 423
*foo **bar***
<p><em>foo <strong>bar</strong></em></p>
Example 424
*foo**bar***
<p><em>foo<strong>bar</strong></em></p>

When the lengths of the interior closing and opening delimiter runs are both multiples of 3, though, they can match to create emphasis:

Example 425
foo***bar***baz
<p>foo<em><strong>bar</strong></em>baz</p>
Example 426
foo******bar*********baz
<p>foo<strong><strong><strong>bar</strong></strong></strong>***baz</p>

Indefinite levels of nesting are possible:

Example 427
*foo **bar *baz* bim** bop*
<p><em>foo <strong>bar <em>baz</em> bim</strong> bop</em></p>
Example 428
*foo [*bar*](/url)*
<p><em>foo <a href="/url"><em>bar</em></a></em></p>

There can be no empty emphasis or strong emphasis:

Example 429
** is not an empty emphasis
<p>** is not an empty emphasis</p>
Example 430
**** is not an empty strong emphasis
<p>**** is not an empty strong emphasis</p>

Rule 10:

Any nonempty sequence of inline elements can be the contents of an strongly emphasized span.

Example 431
**foo [bar](/url)**
<p><strong>foo <a href="/url">bar</a></strong></p>
Example 432
**foo
bar**
<p><strong>foo
bar</strong></p>

In particular, emphasis and strong emphasis can be nested inside strong emphasis:

Example 433
__foo _bar_ baz__
<p><strong>foo <em>bar</em> baz</strong></p>
Example 434
__foo __bar__ baz__
<p><strong>foo <strong>bar</strong> baz</strong></p>
Example 435
____foo__ bar__
<p><strong><strong>foo</strong> bar</strong></p>
Example 436
**foo **bar****
<p><strong>foo <strong>bar</strong></strong></p>
Example 437
**foo *bar* baz**
<p><strong>foo <em>bar</em> baz</strong></p>
Example 438
**foo*bar*baz**
<p><strong>foo<em>bar</em>baz</strong></p>
Example 439
***foo* bar**
<p><strong><em>foo</em> bar</strong></p>
Example 440
**foo *bar***
<p><strong>foo <em>bar</em></strong></p>

Indefinite levels of nesting are possible:

Example 441
**foo *bar **baz**
bim* bop**
<p><strong>foo <em>bar <strong>baz</strong>
bim</em> bop</strong></p>
Example 442
**foo [*bar*](/url)**
<p><strong>foo <a href="/url"><em>bar</em></a></strong></p>

There can be no empty emphasis or strong emphasis:

Example 443
__ is not an empty emphasis
<p>__ is not an empty emphasis</p>
Example 444
____ is not an empty strong emphasis
<p>____ is not an empty strong emphasis</p>

Rule 11:

Example 445
foo ***
<p>foo ***</p>
Example 446
foo *\**
<p>foo <em>*</em></p>
Example 447
foo *_*
<p>foo <em>_</em></p>
Example 448
foo *****
<p>foo *****</p>
Example 449
foo **\***
<p>foo <strong>*</strong></p>
Example 450
foo **_**
<p>foo <strong>_</strong></p>

Note that when delimiters do not match evenly, Rule 11 determines that the excess literal * characters will appear outside of the emphasis, rather than inside it:

Example 451
**foo*
<p>*<em>foo</em></p>
Example 452
*foo**
<p><em>foo</em>*</p>
Example 453
***foo**
<p>*<strong>foo</strong></p>
Example 454
****foo*
<p>***<em>foo</em></p>
Example 455
**foo***
<p><strong>foo</strong>*</p>
Example 456
*foo****
<p><em>foo</em>***</p>

Rule 12:

Example 457
foo ___
<p>foo ___</p>
Example 458
foo _\__
<p>foo <em>_</em></p>
Example 459
foo _*_
<p>foo <em>*</em></p>
Example 460
foo _____
<p>foo _____</p>
Example 461
foo __\___
<p>foo <strong>_</strong></p>
Example 462
foo __*__
<p>foo <strong>*</strong></p>
Example 463
__foo_
<p>_<em>foo</em></p>

Note that when delimiters do not match evenly, Rule 12 determines that the excess literal _ characters will appear outside of the emphasis, rather than inside it:

Example 464
_foo__
<p><em>foo</em>_</p>
Example 465
___foo__
<p>_<strong>foo</strong></p>
Example 466
____foo_
<p>___<em>foo</em></p>
Example 467
__foo___
<p><strong>foo</strong>_</p>
Example 468
_foo____
<p><em>foo</em>___</p>

Rule 13 implies that if you want emphasis nested directly inside emphasis, you must use different delimiters:

Example 469
**foo**
<p><strong>foo</strong></p>
Example 470
*_foo_*
<p><em><em>foo</em></em></p>
Example 471
__foo__
<p><strong>foo</strong></p>
Example 472
_*foo*_
<p><em><em>foo</em></em></p>

However, strong emphasis within strong emphasis is possible without switching delimiters:

Example 473
****foo****
<p><strong><strong>foo</strong></strong></p>
Example 474
____foo____
<p><strong><strong>foo</strong></strong></p>

Rule 13 can be applied to arbitrarily long sequences of delimiters:

Example 475
******foo******
<p><strong><strong><strong>foo</strong></strong></strong></p>

Rule 14:

Example 476
***foo***
<p><em><strong>foo</strong></em></p>
Example 477
_____foo_____
<p><em><strong><strong>foo</strong></strong></em></p>

Rule 15:

Example 478
*foo _bar* baz_
<p><em>foo _bar</em> baz_</p>
Example 479
*foo __bar *baz bim__ bam*
<p><em>foo <strong>bar *baz bim</strong> bam</em></p>

Rule 16:

Example 480
**foo **bar baz**
<p>**foo <strong>bar baz</strong></p>
Example 481
*foo *bar baz*
<p>*foo <em>bar baz</em></p>

Rule 17:

Example 482
*[bar*](/url)
<p>*<a href="/url">bar*</a></p>
Example 483
_foo [bar_](/url)
<p>_foo <a href="/url">bar_</a></p>
Example 484
*<img src="foo" title="*"/>
<p>*<img src="foo" title="*"/></p>
Example 485
**<a href="**">
<p>**<a href="**"></p>
Example 486
__<a href="__">
<p>__<a href="__"></p>
Example 487
*a `*`*
<p><em>a <code>*</code></em></p>
Example 488
_a `_`_
<p><em>a <code>_</code></em></p>
Example 489
**a<http://foo.bar/?q=**>
<p>**a<a href="http://foo.bar/?q=**">http://foo.bar/?q=**</a></p>
Example 490
__a<http://foo.bar/?q=__>
<p>__a<a href="http://foo.bar/?q=__">http://foo.bar/?q=__</a></p>

Strikethrough (extension)

GFM enables the strikethrough extension, where an additional emphasis type is available.

Strikethrough text is any text wrapped in two tildes (~).

Example 491
~~Hi~~ Hello, world!
<p><del>Hi</del> Hello, world!</p>

As with regular emphasis delimiters, a new paragraph will cause strikethrough parsing to cease:

Example 492
This ~~has a

new paragraph~~.
<p>This ~~has a</p>
<p>new paragraph~~.</p>

Links

A link contains [link text] (the visible text), a [link destination] (the URI that is the link destination), and optionally a [link title]. There are two basic kinds of links in Markdown. In [inline links] the destination and title are given immediately after the link text. In [reference links] the destination and title are defined elsewhere in the document.

A link text consists of a sequence of zero or more inline elements enclosed by square brackets ([ and ]). The following rules apply:

A link destination consists of either

A link title consists of either

Although [link titles] may span multiple lines, they may not contain a [blank line].

An inline link consists of a [link text] followed immediately by a left parenthesis (, optional [whitespace], an optional [link destination], an optional [link title] separated from the link destination by [whitespace], optional [whitespace], and a right parenthesis ). The link's text consists of the inlines contained in the [link text] (excluding the enclosing square brackets). The link's URI consists of the link destination, excluding enclosing <...> if present, with backslash-escapes in effect as described above. The link's title consists of the link title, excluding its enclosing delimiters, with backslash-escapes in effect as described above.

Here is a simple inline link:

Example 493
[link](/uri "title")
<p><a href="/uri" title="title">link</a></p>

The title may be omitted:

Example 494
[link](/uri)
<p><a href="/uri">link</a></p>

Both the title and the destination may be omitted:

Example 495
[link]()
<p><a href="">link</a></p>
Example 496
[link](<>)
<p><a href="">link</a></p>

The destination can only contain spaces if it is enclosed in pointy brackets:

Example 497
[link](/my uri)
<p>[link](/my uri)</p>
Example 498
[link](</my uri>)
<p><a href="/my%20uri">link</a></p>

The destination cannot contain line breaks, even if enclosed in pointy brackets:

Example 499
[link](foo
bar)
<p>[link](foo
bar)</p>
Example 500
[link](<foo
bar>)
<p>[link](<foo
bar>)</p>

The destination can contain ) if it is enclosed in pointy brackets:

Example 501
[a](<b)c>)
<p><a href="b)c">a</a></p>

Pointy brackets that enclose links must be unescaped:

Example 502
[link](<foo\>)
<p>[link](&lt;foo&gt;)</p>

These are not links, because the opening pointy bracket is not matched properly:

Example 503
[a](<b)c
[a](<b)c>
[a](<b>c)
<p>[a](&lt;b)c
[a](&lt;b)c&gt;
[a](<b>c)</p>

Parentheses inside the link destination may be escaped:

Example 504
[link](\(foo\))
<p><a href="(foo)">link</a></p>

Any number of parentheses are allowed without escaping, as long as they are balanced:

Example 505
[link](foo(and(bar)))
<p><a href="foo(and(bar))">link</a></p>

However, if you have unbalanced parentheses, you need to escape or use the <...> form:

Example 506
[link](foo\(and\(bar\))
<p><a href="foo(and(bar)">link</a></p>
Example 507
[link](<foo(and(bar)>)
<p><a href="foo(and(bar)">link</a></p>

Parentheses and other symbols can also be escaped, as usual in Markdown:

Example 508
[link](foo\)\:)
<p><a href="foo):">link</a></p>

A link can contain fragment identifiers and queries:

Example 509
[link](#fragment)

[link](http://example.com#fragment)

[link](http://example.com?foo=3#frag)
<p><a href="#fragment">link</a></p>
<p><a href="http://example.com#fragment">link</a></p>
<p><a href="http://example.com?foo=3#frag">link</a></p>

Note that a backslash before a non-escapable character is just a backslash:

Example 510
[link](foo\bar)
<p><a href="foo%5Cbar">link</a></p>

URL-escaping should be left alone inside the destination, as all URL-escaped characters are also valid URL characters. Entity and numerical character references in the destination will be parsed into the corresponding Unicode code points, as usual. These may be optionally URL-escaped when written as HTML, but this spec does not enforce any particular policy for rendering URLs in HTML or other formats. Renderers may make different decisions about how to escape or normalize URLs in the output.

Example 511
[link](foo%20b&auml;)
<p><a href="foo%20b%C3%A4">link</a></p>

Note that, because titles can often be parsed as destinations, if you try to omit the destination and keep the title, you'll get unexpected results:

Example 512
[link]("title")
<p><a href="%22title%22">link</a></p>

Titles may be in single quotes, double quotes, or parentheses:

Example 513
[link](/url "title")
[link](/url 'title')
[link](/url (title))
<p><a href="/url" title="title">link</a>
<a href="/url" title="title">link</a>
<a href="/url" title="title">link</a></p>

Backslash escapes and entity and numeric character references may be used in titles:

Example 514
[link](/url "title \"&quot;")
<p><a href="/url" title="title &quot;&quot;">link</a></p>

Titles must be separated from the link using a [whitespace]. Other [Unicode whitespace] like non-breaking space doesn't work.

Example 515
[link](/url "title")
<p><a href="/url%C2%A0%22title%22">link</a></p>

Nested balanced quotes are not allowed without escaping:

Example 516
[link](/url "title "and" title")
<p>[link](/url &quot;title &quot;and&quot; title&quot;)</p>

But it is easy to work around this by using a different quote type:

Example 517
[link](/url 'title "and" title')
<p><a href="/url" title="title &quot;and&quot; title">link</a></p>

(Note: Markdown.pl did allow double quotes inside a double-quoted title, and its test suite included a test demonstrating this. But it is hard to see a good rationale for the extra complexity this brings, since there are already many ways---backslash escaping, entity and numeric character references, or using a different quote type for the enclosing title---to write titles containing double quotes. Markdown.pl's handling of titles has a number of other strange features. For example, it allows single-quoted titles in inline links, but not reference links. And, in reference links but not inline links, it allows a title to begin with " and end with ). Markdown.pl 1.0.1 even allows titles with no closing quotation mark, though 1.0.2b8 does not. It seems preferable to adopt a simple, rational rule that works the same way in inline links and link reference definitions.)

[Whitespace] is allowed around the destination and title:

Example 518
[link](   /uri
  "title"  )
<p><a href="/uri" title="title">link</a></p>

But it is not allowed between the link text and the following parenthesis:

Example 519
[link] (/uri)
<p>[link] (/uri)</p>

The link text may contain balanced brackets, but not unbalanced ones, unless they are escaped:

Example 520
[link [foo [bar]]](/uri)
<p><a href="/uri">link [foo [bar]]</a></p>
Example 521
[link] bar](/uri)
<p>[link] bar](/uri)</p>
Example 522
[link [bar](/uri)
<p>[link <a href="/uri">bar</a></p>
Example 523
[link \[bar](/uri)
<p><a href="/uri">link [bar</a></p>

The link text may contain inline content:

Example 524
[link *foo **bar** `#`*](/uri)
<p><a href="/uri">link <em>foo <strong>bar</strong> <code>#</code></em></a></p>
Example 525
[![moon](moon.jpg)](/uri)
<p><a href="/uri"><img src="moon.jpg" alt="moon" /></a></p>

However, links may not contain other links, at any level of nesting.

Example 526
[foo [bar](/uri)](/uri)
<p>[foo <a href="/uri">bar</a>](/uri)</p>
Example 527
[foo *[bar [baz](/uri)](/uri)*](/uri)
<p>[foo <em>[bar <a href="/uri">baz</a>](/uri)</em>](/uri)</p>
Example 528
![[[foo](uri1)](uri2)](uri3)
<p><img src="uri3" alt="[foo](uri2)" /></p>

These cases illustrate the precedence of link text grouping over emphasis grouping:

Example 529
*[foo*](/uri)
<p>*<a href="/uri">foo*</a></p>
Example 530
[foo *bar](baz*)
<p><a href="baz*">foo *bar</a></p>

Note that brackets that aren't part of links do not take precedence:

Example 531
*foo [bar* baz]
<p><em>foo [bar</em> baz]</p>

These cases illustrate the precedence of HTML tags, code spans, and autolinks over link grouping:

Example 532
[foo <bar attr="](baz)">
<p>[foo <bar attr="](baz)"></p>
Example 533
[foo`](/uri)`
<p>[foo<code>](/uri)</code></p>
Example 534
[foo<http://example.com/?search=](uri)>
<p>[foo<a href="http://example.com/?search=%5D(uri)">http://example.com/?search=](uri)</a></p>

There are three kinds of reference links: full, collapsed, and shortcut.

A full reference link consists of a [link text] immediately followed by a [link label] that [matches] a [link reference definition] elsewhere in the document.

A link label begins with a left bracket ([) and ends with the first right bracket (]) that is not backslash-escaped. Between these brackets there must be at least one [non-whitespace character]. Unescaped square bracket characters are not allowed inside the opening and closing square brackets of [link labels]. A link label can have at most 999 characters inside the square brackets.

One label matches another just in case their normalized forms are equal. To normalize a label, strip off the opening and closing brackets, perform the Unicode case fold, strip leading and trailing [whitespace] and collapse consecutive internal [whitespace] to a single space. If there are multiple matching reference link definitions, the one that comes first in the document is used. (It is desirable in such cases to emit a warning.)

The contents of the first link label are parsed as inlines, which are used as the link's text. The link's URI and title are provided by the matching [link reference definition].

Here is a simple example:

Example 535
[foo][bar]

[bar]: /url "title"
<p><a href="/url" title="title">foo</a></p>

The rules for the [link text] are the same as with [inline links]. Thus:

The link text may contain balanced brackets, but not unbalanced ones, unless they are escaped:

Example 536
[link [foo [bar]]][ref]

[ref]: /uri
<p><a href="/uri">link [foo [bar]]</a></p>
Example 537
[link \[bar][ref]

[ref]: /uri
<p><a href="/uri">link [bar</a></p>

The link text may contain inline content:

Example 538
[link *foo **bar** `#`*][ref]

[ref]: /uri
<p><a href="/uri">link <em>foo <strong>bar</strong> <code>#</code></em></a></p>
Example 539
[![moon](moon.jpg)][ref]

[ref]: /uri
<p><a href="/uri"><img src="moon.jpg" alt="moon" /></a></p>

However, links may not contain other links, at any level of nesting.

Example 540
[foo [bar](/uri)][ref]

[ref]: /uri
<p>[foo <a href="/uri">bar</a>]<a href="/uri">ref</a></p>
Example 541
[foo *bar [baz][ref]*][ref]

[ref]: /uri
<p>[foo <em>bar <a href="/uri">baz</a></em>]<a href="/uri">ref</a></p>

(In the examples above, we have two [shortcut reference links] instead of one [full reference link].)

The following cases illustrate the precedence of link text grouping over emphasis grouping:

Example 542
*[foo*][ref]

[ref]: /uri
<p>*<a href="/uri">foo*</a></p>
Example 543
[foo *bar][ref]

[ref]: /uri
<p><a href="/uri">foo *bar</a></p>

These cases illustrate the precedence of HTML tags, code spans, and autolinks over link grouping:

Example 544
[foo <bar attr="][ref]">

[ref]: /uri
<p>[foo <bar attr="][ref]"></p>
Example 545
[foo`][ref]`

[ref]: /uri
<p>[foo<code>][ref]</code></p>
Example 546
[foo<http://example.com/?search=][ref]>

[ref]: /uri
<p>[foo<a href="http://example.com/?search=%5D%5Bref%5D">http://example.com/?search=][ref]</a></p>

Matching is case-insensitive:

Example 547
[foo][BaR]

[bar]: /url "title"
<p><a href="/url" title="title">foo</a></p>

Unicode case fold is used:

Example 548
[Толпой][Толпой] is a Russian word.

[ТОЛПОЙ]: /url
<p><a href="/url">Толпой</a> is a Russian word.</p>

Consecutive internal [whitespace] is treated as one space for purposes of determining matching:

Example 549
[Foo
  bar]: /url

[Baz][Foo bar]
<p><a href="/url">Baz</a></p>

No [whitespace] is allowed between the [link text] and the [link label]:

Example 550
[foo] [bar]

[bar]: /url "title"
<p>[foo] <a href="/url" title="title">bar</a></p>
Example 551
[foo]
[bar]

[bar]: /url "title"
<p>[foo]
<a href="/url" title="title">bar</a></p>

This is a departure from John Gruber's original Markdown syntax description, which explicitly allows whitespace between the link text and the link label. It brings reference links in line with [inline links], which (according to both original Markdown and this spec) cannot have whitespace after the link text. More importantly, it prevents inadvertent capture of consecutive [shortcut reference links]. If whitespace is allowed between the link text and the link label, then in the following we will have a single reference link, not two shortcut reference links, as intended:

[foo]
[bar]

[foo]: /url1
[bar]: /url2

(Note that [shortcut reference links] were introduced by Gruber himself in a beta version of Markdown.pl, but never included in the official syntax description. Without shortcut reference links, it is harmless to allow space between the link text and link label; but once shortcut references are introduced, it is too dangerous to allow this, as it frequently leads to unintended results.)

When there are multiple matching [link reference definitions], the first is used:

Example 552
[foo]: /url1

[foo]: /url2

[bar][foo]
<p><a href="/url1">bar</a></p>

Note that matching is performed on normalized strings, not parsed inline content. So the following does not match, even though the labels define equivalent inline content:

Example 553
[bar][foo\!]

[foo!]: /url
<p>[bar][foo!]</p>

[Link labels] cannot contain brackets, unless they are backslash-escaped:

Example 554
[foo][ref[]

[ref[]: /uri
<p>[foo][ref[]</p>
<p>[ref[]: /uri</p>
Example 555
[foo][ref[bar]]

[ref[bar]]: /uri
<p>[foo][ref[bar]]</p>
<p>[ref[bar]]: /uri</p>
Example 556
[[[foo]]]

[[[foo]]]: /url
<p>[[[foo]]]</p>
<p>[[[foo]]]: /url</p>
Example 557
[foo][ref\[]

[ref\[]: /uri
<p><a href="/uri">foo</a></p>

Note that in this example ] is not backslash-escaped:

Example 558
[bar\\]: /uri

[bar\\]
<p><a href="/uri">bar\</a></p>

A [link label] must contain at least one [non-whitespace character]:

Example 559
[]

[]: /uri
<p>[]</p>
<p>[]: /uri</p>
Example 560
[
 ]

[
 ]: /uri
<p>[
]</p>
<p>[
]: /uri</p>

A collapsed reference link consists of a [link label] that [matches] a [link reference definition] elsewhere in the document, followed by the string []. The contents of the first link label are parsed as inlines, which are used as the link's text. The link's URI and title are provided by the matching reference link definition. Thus, [foo][] is equivalent to [foo][foo].

Example 561
[foo][]

[foo]: /url "title"
<p><a href="/url" title="title">foo</a></p>
Example 562
[*foo* bar][]

[*foo* bar]: /url "title"
<p><a href="/url" title="title"><em>foo</em> bar</a></p>

The link labels are case-insensitive:

Example 563
[Foo][]

[foo]: /url "title"
<p><a href="/url" title="title">Foo</a></p>

As with full reference links, [whitespace] is not allowed between the two sets of brackets:

Example 564
[foo] 
[]

[foo]: /url "title"
<p><a href="/url" title="title">foo</a>
[]</p>

A shortcut reference link consists of a [link label] that [matches] a [link reference definition] elsewhere in the document and is not followed by [] or a link label. The contents of the first link label are parsed as inlines, which are used as the link's text. The link's URI and title are provided by the matching link reference definition. Thus, [foo] is equivalent to [foo][].

Example 565
[foo]

[foo]: /url "title"
<p><a href="/url" title="title">foo</a></p>
Example 566
[*foo* bar]

[*foo* bar]: /url "title"
<p><a href="/url" title="title"><em>foo</em> bar</a></p>
Example 567
[[*foo* bar]]

[*foo* bar]: /url "title"
<p>[<a href="/url" title="title"><em>foo</em> bar</a>]</p>
Example 568
[[bar [foo]

[foo]: /url
<p>[[bar <a href="/url">foo</a></p>

The link labels are case-insensitive:

Example 569
[Foo]

[foo]: /url "title"
<p><a href="/url" title="title">Foo</a></p>

A space after the link text should be preserved:

Example 570
[foo] bar

[foo]: /url
<p><a href="/url">foo</a> bar</p>

If you just want bracketed text, you can backslash-escape the opening bracket to avoid links:

Example 571
\[foo]

[foo]: /url "title"
<p>[foo]</p>

Note that this is a link, because a link label ends with the first following closing bracket:

Example 572
[foo*]: /url

*[foo*]
<p>*<a href="/url">foo*</a></p>

Full and compact references take precedence over shortcut references:

Example 573
[foo][bar]

[foo]: /url1
[bar]: /url2
<p><a href="/url2">foo</a></p>
Example 574
[foo][]

[foo]: /url1
<p><a href="/url1">foo</a></p>

Inline links also take precedence:

Example 575
[foo]()

[foo]: /url1
<p><a href="">foo</a></p>
Example 576
[foo](not a link)

[foo]: /url1
<p><a href="/url1">foo</a>(not a link)</p>

In the following case [bar][baz] is parsed as a reference, [foo] as normal text:

Example 577
[foo][bar][baz]

[baz]: /url
<p>[foo]<a href="/url">bar</a></p>

Here, though, [foo][bar] is parsed as a reference, since [bar] is defined:

Example 578
[foo][bar][baz]

[baz]: /url1
[bar]: /url2
<p><a href="/url2">foo</a><a href="/url1">baz</a></p>

Here [foo] is not parsed as a shortcut reference, because it is followed by a link label (even though [bar] is not defined):

Example 579
[foo][bar][baz]

[baz]: /url1
[foo]: /url2
<p>[foo]<a href="/url1">bar</a></p>

Images

Syntax for images is like the syntax for links, with one difference. Instead of [link text], we have an image description. The rules for this are the same as for [link text], except that (a) an image description starts with ![ rather than [, and (b) an image description may contain links. An image description has inline elements as its contents. When an image is rendered to HTML, this is standardly used as the image's alt attribute.

Example 580
![foo](/url "title")
<p><img src="/url" alt="foo" title="title" /></p>
Example 581
![foo *bar*]

[foo *bar*]: train.jpg "train & tracks"
<p><img src="train.jpg" alt="foo bar" title="train &amp; tracks" /></p>
Example 582
![foo ![bar](/url)](/url2)
<p><img src="/url2" alt="foo bar" /></p>
Example 583
![foo [bar](/url)](/url2)
<p><img src="/url2" alt="foo bar" /></p>

Though this spec is concerned with parsing, not rendering, it is recommended that in rendering to HTML, only the plain string content of the [image description] be used. Note that in the above example, the alt attribute's value is foo bar, not foo [bar](/url) or foo <a href="/url">bar</a>. Only the plain string content is rendered, without formatting.

Example 584
![foo *bar*][]

[foo *bar*]: train.jpg "train & tracks"
<p><img src="train.jpg" alt="foo bar" title="train &amp; tracks" /></p>
Example 585
![foo *bar*][foobar]

[FOOBAR]: train.jpg "train & tracks"
<p><img src="train.jpg" alt="foo bar" title="train &amp; tracks" /></p>
Example 586
![foo](train.jpg)
<p><img src="train.jpg" alt="foo" /></p>
Example 587
My ![foo bar](/path/to/train.jpg  "title"   )
<p>My <img src="/path/to/train.jpg" alt="foo bar" title="title" /></p>
Example 588
![foo](<url>)
<p><img src="url" alt="foo" /></p>
Example 589
![](/url)
<p><img src="/url" alt="" /></p>

Reference-style:

Example 590
![foo][bar]

[bar]: /url
<p><img src="/url" alt="foo" /></p>
Example 591
![foo][bar]

[BAR]: /url
<p><img src="/url" alt="foo" /></p>

Collapsed:

Example 592
![foo][]

[foo]: /url "title"
<p><img src="/url" alt="foo" title="title" /></p>
Example 593
![*foo* bar][]

[*foo* bar]: /url "title"
<p><img src="/url" alt="foo bar" title="title" /></p>

The labels are case-insensitive:

Example 594
![Foo][]

[foo]: /url "title"
<p><img src="/url" alt="Foo" title="title" /></p>

As with reference links, [whitespace] is not allowed between the two sets of brackets:

Example 595
![foo] 
[]

[foo]: /url "title"
<p><img src="/url" alt="foo" title="title" />
[]</p>

Shortcut:

Example 596
![foo]

[foo]: /url "title"
<p><img src="/url" alt="foo" title="title" /></p>
Example 597
![*foo* bar]

[*foo* bar]: /url "title"
<p><img src="/url" alt="foo bar" title="title" /></p>

Note that link labels cannot contain unescaped brackets:

Example 598
![[foo]]

[[foo]]: /url "title"
<p>![[foo]]</p>
<p>[[foo]]: /url &quot;title&quot;</p>

The link labels are case-insensitive:

Example 599
![Foo]

[foo]: /url "title"
<p><img src="/url" alt="Foo" title="title" /></p>

If you just want a literal ! followed by bracketed text, you can backslash-escape the opening [:

Example 600
!\[foo]

[foo]: /url "title"
<p>![foo]</p>

If you want a link after a literal !, backslash-escape the !:

Example 601
\![foo]

[foo]: /url "title"
<p>!<a href="/url" title="title">foo</a></p>

Autolinks

Autolinks are absolute URIs and email addresses inside < and >. They are parsed as links, with the URL or email address as the link label.

A URI autolink consists of <, followed by an [absolute URI] followed by >. It is parsed as a link to the URI, with the URI as the link's label.

An absolute URI, for these purposes, consists of a [scheme] followed by a colon (:) followed by zero or more characters other than ASCII [whitespace] and control characters, <, and >. If the URI includes these characters, they must be percent-encoded (e.g. %20 for a space).

For purposes of this spec, a scheme is any sequence of 2--32 characters beginning with an ASCII letter and followed by any combination of ASCII letters, digits, or the symbols plus ("+"), period ("."), or hyphen ("-").

Here are some valid autolinks:

Example 602
<http://foo.bar.baz>
<p><a href="http://foo.bar.baz">http://foo.bar.baz</a></p>
Example 603
<http://foo.bar.baz/test?q=hello&id=22&boolean>
<p><a href="http://foo.bar.baz/test?q=hello&amp;id=22&amp;boolean">http://foo.bar.baz/test?q=hello&amp;id=22&amp;boolean</a></p>
Example 604
<irc://foo.bar:2233/baz>
<p><a href="irc://foo.bar:2233/baz">irc://foo.bar:2233/baz</a></p>

Uppercase is also fine:

Example 605
<MAILTO:FOO@BAR.BAZ>
<p><a href="MAILTO:FOO@BAR.BAZ">MAILTO:FOO@BAR.BAZ</a></p>

Note that many strings that count as [absolute URIs] for purposes of this spec are not valid URIs, because their schemes are not registered or because of other problems with their syntax:

Example 606
<a+b+c:d>
<p><a href="a+b+c:d">a+b+c:d</a></p>
Example 607
<made-up-scheme://foo,bar>
<p><a href="made-up-scheme://foo,bar">made-up-scheme://foo,bar</a></p>
Example 608
<http://../>
<p><a href="http://../">http://../</a></p>
Example 609
<localhost:5001/foo>
<p><a href="localhost:5001/foo">localhost:5001/foo</a></p>

Spaces are not allowed in autolinks:

Example 610
<http://foo.bar/baz bim>
<p>&lt;http://foo.bar/baz bim&gt;</p>

Backslash-escapes do not work inside autolinks:

Example 611
<http://example.com/\[\>
<p><a href="http://example.com/%5C%5B%5C">http://example.com/\[\</a></p>

An email autolink consists of <, followed by an [email address], followed by >. The link's label is the email address, and the URL is mailto: followed by the email address.

An email address, for these purposes, is anything that matches the non-normative regex from the HTML5 spec:

/^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?
(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/

Examples of email autolinks:

Example 612
<foo@bar.example.com>
<p><a href="mailto:foo@bar.example.com">foo@bar.example.com</a></p>
Example 613
<foo+special@Bar.baz-bar0.com>
<p><a href="mailto:foo+special@Bar.baz-bar0.com">foo+special@Bar.baz-bar0.com</a></p>

Backslash-escapes do not work inside email autolinks:

Example 614
<foo\+@bar.example.com>
<p>&lt;foo+@bar.example.com&gt;</p>

These are not autolinks:

Example 615
<>
<p>&lt;&gt;</p>
Example 616
< http://foo.bar >
<p>&lt; http://foo.bar &gt;</p>
Example 617
<m:abc>
<p>&lt;m:abc&gt;</p>
Example 618
<foo.bar.baz>
<p>&lt;foo.bar.baz&gt;</p>
Example 619
http://example.com
<p>http://example.com</p>
Example 620
foo@bar.example.com
<p>foo@bar.example.com</p>

Autolinks (extension)

GFM enables the autolink extension, where autolinks will be recognised in a greater number of conditions.

[Autolink]s can also be constructed without requiring the use of < and to > to delimit them, although they will be recognized under a smaller set of circumstances. All such recognized autolinks can only come at the beginning of a line, after whitespace, or any of the delimiting characters *, _, ~, and (.

An extended www autolink will be recognized when the text www. is found followed by a [valid domain]. A valid domain consists of segments of alphanumeric characters, underscores (_) and hyphens (-) separated by periods (.). There must be at least one period, and no underscores may be present in the last two segments of the domain.

The scheme http will be inserted automatically:

Example 621
www.commonmark.org
<p><a href="http://www.commonmark.org">www.commonmark.org</a></p>

After a [valid domain], zero or more non-space non-< characters may follow:

Example 622
Visit www.commonmark.org/help for more information.
<p>Visit <a href="http://www.commonmark.org/help">www.commonmark.org/help</a> for more information.</p>

We then apply extended autolink path validation as follows:

Trailing punctuation (specifically, ?, !, ., ,, :, *, _, and ~) will not be considered part of the autolink, though they may be included in the interior of the link:

Example 623
Visit www.commonmark.org.

Visit www.commonmark.org/a.b.
<p>Visit <a href="http://www.commonmark.org">www.commonmark.org</a>.</p>
<p>Visit <a href="http://www.commonmark.org/a.b">www.commonmark.org/a.b</a>.</p>

When an autolink ends in ), we scan the entire autolink for the total number of parentheses. If there is a greater number of closing parentheses than opening ones, we don't consider the unmatched trailing parentheses part of the autolink, in order to facilitate including an autolink inside a parenthesis:

Example 624
www.google.com/search?q=Markup+(business)

www.google.com/search?q=Markup+(business)))

(www.google.com/search?q=Markup+(business))

(www.google.com/search?q=Markup+(business)
<p><a href="http://www.google.com/search?q=Markup+(business)">www.google.com/search?q=Markup+(business)</a></p>
<p><a href="http://www.google.com/search?q=Markup+(business)">www.google.com/search?q=Markup+(business)</a>))</p>
<p>(<a href="http://www.google.com/search?q=Markup+(business)">www.google.com/search?q=Markup+(business)</a>)</p>
<p>(<a href="http://www.google.com/search?q=Markup+(business)">www.google.com/search?q=Markup+(business)</a></p>

This check is only done when the link ends in a closing parentheses ), so if the only parentheses are in the interior of the autolink, no special rules are applied:

Example 625
www.google.com/search?q=(business))+ok
<p><a href="http://www.google.com/search?q=(business))+ok">www.google.com/search?q=(business))+ok</a></p>

If an autolink ends in a semicolon (;), we check to see if it appears to resemble an [entity reference][entity references]; if the preceding text is & followed by one or more alphanumeric characters. If so, it is excluded from the autolink:

Example 626
www.google.com/search?q=commonmark&hl=en

www.google.com/search?q=commonmark&hl;
<p><a href="http://www.google.com/search?q=commonmark&amp;hl=en">www.google.com/search?q=commonmark&amp;hl=en</a></p>
<p><a href="http://www.google.com/search?q=commonmark">www.google.com/search?q=commonmark</a>&amp;hl;</p>

< immediately ends an autolink.

Example 627
www.commonmark.org/he<lp
<p><a href="http://www.commonmark.org/he">www.commonmark.org/he</a>&lt;lp</p>

An extended url autolink will be recognised when one of the schemes http://, https://, or ftp://, followed by a [valid domain], then zero or more non-space non-< characters according to [extended autolink path validation]:

Example 628
http://commonmark.org

(Visit https://encrypted.google.com/search?q=Markup+(business))

Anonymous FTP is available at ftp://foo.bar.baz.
<p><a href="http://commonmark.org">http://commonmark.org</a></p>
<p>(Visit <a href="https://encrypted.google.com/search?q=Markup+(business)">https://encrypted.google.com/search?q=Markup+(business)</a>)</p>
<p>Anonymous FTP is available at <a href="ftp://foo.bar.baz">ftp://foo.bar.baz</a>.</p>

An extended email autolink will be recognised when an email address is recognised within any text node. Email addresses are recognised according to the following rules:

The scheme mailto: will automatically be added to the generated link:

Example 629
foo@bar.baz
<p><a href="mailto:foo@bar.baz">foo@bar.baz</a></p>

+ can occur before the @, but not after.

Example 630
hello@mail+xyz.example isn't valid, but hello+xyz@mail.example is.
<p>hello@mail+xyz.example isn't valid, but <a href="mailto:hello+xyz@mail.example">hello+xyz@mail.example</a> is.</p>

., -, and _ can occur on both sides of the @, but only . may occur at the end of the email address, in which case it will not be considered part of the address:

Example 631
a.b-c_d@a.b

a.b-c_d@a.b.

a.b-c_d@a.b-

a.b-c_d@a.b_
<p><a href="mailto:a.b-c_d@a.b">a.b-c_d@a.b</a></p>
<p><a href="mailto:a.b-c_d@a.b">a.b-c_d@a.b</a>.</p>
<p>a.b-c_d@a.b-</p>
<p>a.b-c_d@a.b_</p>

Raw HTML

Text between < and > that looks like an HTML tag is parsed as a raw HTML tag and will be rendered in HTML without escaping. Tag and attribute names are not limited to current HTML tags, so custom tags (and even, say, DocBook tags) may be used.

Here is the grammar for tags:

A tag name consists of an ASCII letter followed by zero or more ASCII letters, digits, or hyphens (-).

An attribute consists of [whitespace], an [attribute name], and an optional [attribute value specification].

An attribute name consists of an ASCII letter, _, or :, followed by zero or more ASCII letters, digits, _, ., :, or -. (Note: This is the XML specification restricted to ASCII. HTML5 is laxer.)

An attribute value specification consists of optional [whitespace], a = character, optional [whitespace], and an [attribute value].

An attribute value consists of an [unquoted attribute value], a [single-quoted attribute value], or a [double-quoted attribute value].

An unquoted attribute value is a nonempty string of characters not including [whitespace], ", ', =, <, >, or `.

A single-quoted attribute value consists of ', zero or more characters not including ', and a final '.

A double-quoted attribute value consists of ", zero or more characters not including ", and a final ".

An open tag consists of a < character, a [tag name], zero or more [attributes], optional [whitespace], an optional / character, and a > character.

A closing tag consists of the string </, a [tag name], optional [whitespace], and the character >.

An HTML comment consists of <!-- + text + -->, where text does not start with > or ->, does not end with -, and does not contain --. (See the HTML5 spec.)

A processing instruction consists of the string <?, a string of characters not including the string ?>, and the string ?>.

A declaration consists of the string <!, a name consisting of one or more uppercase ASCII letters, [whitespace], a string of characters not including the character >, and the character >.

A CDATA section consists of the string <![CDATA[, a string of characters not including the string ]]>, and the string ]]>.

An HTML tag consists of an [open tag], a [closing tag], an [HTML comment], a [processing instruction], a [declaration], or a [CDATA section].

Here are some simple open tags:

Example 632
<a><bab><c2c>
<p><a><bab><c2c></p>

Empty elements:

Example 633
<a/><b2/>
<p><a/><b2/></p>

[Whitespace] is allowed:

Example 634
<a  /><b2
data="foo" >
<p><a  /><b2
data="foo" ></p>

With attributes:

Example 635
<a foo="bar" bam = 'baz <em>"</em>'
_boolean zoop:33=zoop:33 />
<p><a foo="bar" bam = 'baz <em>"</em>'
_boolean zoop:33=zoop:33 /></p>

Custom tag names can be used:

Example 636
Foo <responsive-image src="foo.jpg" />
<p>Foo <responsive-image src="foo.jpg" /></p>

Illegal tag names, not parsed as HTML:

Example 637
<33> <__>
<p>&lt;33&gt; &lt;__&gt;</p>

Illegal attribute names:

Example 638
<a h*#ref="hi">
<p>&lt;a h*#ref=&quot;hi&quot;&gt;</p>

Illegal attribute values:

Example 639
<a href="hi'> <a href=hi'>
<p>&lt;a href=&quot;hi'&gt; &lt;a href=hi'&gt;</p>

Illegal [whitespace]:

Example 640
< a><
foo><bar/ >
<foo bar=baz
bim!bop />
<p>&lt; a&gt;&lt;
foo&gt;&lt;bar/ &gt;
&lt;foo bar=baz
bim!bop /&gt;</p>

Missing [whitespace]:

Example 641
<a href='bar'title=title>
<p>&lt;a href='bar'title=title&gt;</p>

Closing tags:

Example 642
</a></foo >
<p></a></foo ></p>

Illegal attributes in closing tag:

Example 643
</a href="foo">
<p>&lt;/a href=&quot;foo&quot;&gt;</p>

Comments:

Example 644
foo <!-- this is a
comment - with hyphen -->
<p>foo <!-- this is a
comment - with hyphen --></p>
Example 645
foo <!-- not a comment -- two hyphens -->
<p>foo &lt;!-- not a comment -- two hyphens --&gt;</p>

Not comments:

Example 646
foo <!--> foo -->

foo <!-- foo--->
<p>foo &lt;!--&gt; foo --&gt;</p>
<p>foo &lt;!-- foo---&gt;</p>

Processing instructions:

Example 647
foo <?php echo $a; ?>
<p>foo <?php echo $a; ?></p>

Declarations:

Example 648
foo <!ELEMENT br EMPTY>
<p>foo <!ELEMENT br EMPTY></p>

CDATA sections:

Example 649
foo <![CDATA[>&<]]>
<p>foo <![CDATA[>&<]]></p>

Entity and numeric character references are preserved in HTML attributes:

Example 650
foo <a href="&ouml;">
<p>foo <a href="&ouml;"></p>

Backslash escapes do not work in HTML attributes:

Example 651
foo <a href="\*">
<p>foo <a href="\*"></p>
Example 652
<a href="\"">
<p>&lt;a href=&quot;&quot;&quot;&gt;</p>

Disallowed Raw HTML (extension)

GFM enables the tagfilter extension, where the following HTML tags will be filtered when rendering HTML output:

Filtering is done by replacing the leading < with the entity &lt;. These tags are chosen in particular as they change how HTML is interpreted in a way unique to them (i.e. nested HTML is interpreted differently), and this is usually undesireable in the context of other rendered Markdown content.

All other HTML tags are left untouched.

Example 653
<strong> <title> <style> <em>

<blockquote>
  <xmp> is disallowed.  <XMP> is also disallowed.
</blockquote>
<p><strong> &lt;title> &lt;style> <em></p>
<blockquote>
  &lt;xmp> is disallowed.  &lt;XMP> is also disallowed.
</blockquote>

Hard line breaks

A line break (not in a code span or HTML tag) that is preceded by two or more spaces and does not occur at the end of a block is parsed as a hard line break (rendered in HTML as a <br /> tag):

Example 654
foo  
baz
<p>foo<br />
baz</p>

For a more visible alternative, a backslash before the [line ending] may be used instead of two spaces:

Example 655
foo\
baz
<p>foo<br />
baz</p>

More than two spaces can be used:

Example 656
foo       
baz
<p>foo<br />
baz</p>

Leading spaces at the beginning of the next line are ignored:

Example 657
foo  
     bar
<p>foo<br />
bar</p>
Example 658
foo\
     bar
<p>foo<br />
bar</p>

Line breaks can occur inside emphasis, links, and other constructs that allow inline content:

Example 659
*foo  
bar*
<p><em>foo<br />
bar</em></p>
Example 660
*foo\
bar*
<p><em>foo<br />
bar</em></p>

Line breaks do not occur inside code spans

Example 661
`code  
span`
<p><code>code   span</code></p>
Example 662
`code\
span`
<p><code>code\ span</code></p>

or HTML tags:

Example 663
<a href="foo  
bar">
<p><a href="foo  
bar"></p>
Example 664
<a href="foo\
bar">
<p><a href="foo\
bar"></p>

Hard line breaks are for separating inline content within a block. Neither syntax for hard line breaks works at the end of a paragraph or other block element:

Example 665
foo\
<p>foo\</p>
Example 666
foo  
<p>foo</p>
Example 667
### foo\
<h3>foo\</h3>
Example 668
### foo  
<h3>foo</h3>

Soft line breaks

A regular line break (not in a code span or HTML tag) that is not preceded by two or more spaces or a backslash is parsed as a softbreak. (A softbreak may be rendered in HTML either as a [line ending] or as a space. The result will be the same in browsers. In the examples here, a [line ending] will be used.)

Example 669
foo
baz
<p>foo
baz</p>

Spaces at the end of the line and beginning of the next line are removed:

Example 670
foo 
 baz
<p>foo
baz</p>

A conforming parser may render a soft line break in HTML either as a line break or as a space.

A renderer may also provide an option to render soft line breaks as hard line breaks.

Textual content

Any characters not given an interpretation by the above rules will be parsed as plain textual content.

Example 671
hello $.;'there
<p>hello $.;'there</p>
Example 672
Foo χρῆν
<p>Foo χρῆν</p>

Internal spaces are preserved verbatim:

Example 673
Multiple     spaces
<p>Multiple     spaces</p>

GitLab Official Specification Markdown

Note: This specification is a work in progress. Only some of the official GLFM extensions are defined. We will continue to add any additional ones found in the user-facing documentation for GitLab Flavored Markdown.

There is currently only this single top-level heading, but the examples may be split into multiple top-level headings in the future.

Task list items

See Task lists in the GitLab Flavored Markdown documentation.

Task list items (checkboxes) are defined as a GitHub Flavored Markdown extension in a section above. GitLab extends the behavior of task list items to support additional features. Some of these features are in-progress, and should not yet be considered part of the official GitLab Flavored Markdown specification.

Some of the behavior of task list items is implemented as client-side JavaScript/CSS.

The following are some basic examples; more examples may be added in the future.

Incomplete task:

Example 674
- [ ] incomplete
<ul>
<li>
<task-button/>
<input type="checkbox" disabled/>
incomplete
</li>
</ul>

Completed task:

Example 675
- [x] completed
<ul>
<li>
<task-button/>
<input type="checkbox" checked disabled/>
completed
</li>
</ul>

Inapplicable task:

Example 676
- [~] inapplicable
<ul>
<li>
<task-button/>
<input type="checkbox" data-inapplicable disabled>
<s>
inapplicable
</s>
</li>
</ul>

Inapplicable task in a "loose" list. Note that the <del> tag is not applied to the loose text; it has strikethrough applied with CSS.

Example 677
- [~] inapplicable

  text in loose list
<ul>
<li>
<p>
<task-button/>
<input type="checkbox" data-inapplicable disabled>
<s>
inapplicable
</s>
</p>
<p>
text in loose list
</p>
</li>
</ul>

Front matter

See Front matter in the GitLab Flavored Markdown documentation.

Front matter is metadata included at the beginning of a Markdown document, preceding the content. This data can be used by static site generators like Jekyll, Hugo, and many other applications.

YAML front matter:

Example 678
---
title: YAML front matter
---
<pre>
<code>
title: YAML front matter
</code>
</pre>

TOML front matter:

Example 679
+++
title: TOML front matter
+++
<pre>
<code>
title: TOML front matter
</code>
</pre>

JSON front matter:

Example 680
;;;
{
  "title": "JSON front matter"
}
;;;
<pre>
<code>
{
  "title": "JSON front matter"
}
</code>
</pre>

Front matter blocks should be inserted at the top of the document:

Example 681
text

---
title: YAML front matter
---
<p>text</p>
<hr>
<h2>title: YAML front matter</h2>

Front matter block delimiters shouldn’t be preceded by space characters:

Example 682
 ---
title: YAML front matter
---
<hr>
<h2>title: YAML front matter</h2>

Table of contents

See table of contents in the GitLab Flavored Markdown documentation.

NOTE: Because of this bug (https://gitlab.com/gitlab-org/gitlab/-/issues/359077), we cannot actually include the TOC tag with single brackets in backticks in this Markdown document, otherwise it would render a table of contents inline right here. So, it's been switched to [ + TOC + ] instead. This can be reverted once that bug is fixed.

A table of contents is an unordered list that links to subheadings in the document. Add either the [[_TOC_]] tag or the [ + TOC + ] tag on its own line.

Example 683
[TOC]

# Heading 1

## Heading 2
<nav>
  <ul>
    <li><a href="#heading-1">Heading 1</a></li>
    <ul>
      <li><a href="#heading-2">Heading 2</a></li>
    </ul>
  </ul>
</nav>
<h1>Heading 1</h1>
<h2>Heading 2</h2>
Example 684
[[_TOC_]]

# Heading 1

## Heading 2
<nav>
  <ul>
    <li><a href="#heading-1">Heading 1</a></li>
    <ul>
      <li><a href="#heading-2">Heading 2</a></li>
    </ul>
  </ul>
</nav>
<h1>Heading 1</h1>
<h2>Heading 2</h2>

A table of contents is a block element. It should preceded and followed by a blank line.

Example 685
[[_TOC_]]
text

text
[TOC]
<p>[[<em>TOC</em>]]text</p>
<p>text[TOC]</p>

A table of contents can be indented with up to three spaces.

Example 686
   [[_TOC_]]

# Heading 1
<nav>
  <ul>
    <li><a href="#heading-1">Heading 1</a></li>
  </ul>
</nav>
<h1>Heading 1</h1>

GitLab Internal Extension Markdown

Audio

See audio in the GitLab Flavored Markdown documentation.

GLFM renders image elements as an audio player as long as the resource’s file extension is one of the following supported audio extensions .mp3, .oga, .ogg, .spx, and .wav. Audio ignore the alternative text part of an image declaration.

Example 687
![audio](audio.oga "audio title")
<p><audio src="audio.oga" title="audio title"></audio></p>

Reference definitions work audio as well:

Example 688
[audio]: audio.oga "audio title"

![audio][audio]
<p><audio src="audio.oga" title="audio title"></audio></p>

Video

See videos in the GitLab Flavored Markdown documentation.

GLFM renders image elements as a video player as long as the resource’s file extension is one of the following supported video extensions .mp4, .m4v, .mov, .webm, and .ogv. Videos ignore the alternative text part of an image declaration.

Example 689
![video](video.m4v "video title")
<p><video src="video.m4v" title="video title"></video></p>

Reference definitions work video as well:

Example 690
[video]: video.mov "video title"

![video][video]
<p><video src="video.mov" title="video title"></video></p>

Markdown Preview API Request Overrides

This section contains examples of all controllers which use PreviewMarkdown module and use different markdown_context_params. They exercise the various preview_markdown endpoints via glfm_example_metadata.yml.

preview_markdown exercising groups API endpoint and UploadLinkFilter:

Example 691
[groups-test-file](/uploads/groups-test-file)
<p><a href="groups-test-file">groups-test-file</a></p>

preview_markdown exercising projects API endpoint and RepositoryLinkFilter:

Example 692
[projects-test-file](projects-test-file)
<p><a href="projects-test-file">projects-test-file</a></p>

preview_markdown exercising projects API endpoint and SnippetReferenceFilter:

Example 693
This project snippet ID reference IS filtered: $88888
<p>This project snippet ID reference IS filtered: $88888</p>

preview_markdown exercising personal (non-project) snippets API endpoint. This is only used by the comment field on personal snippets. It has no unique custom markdown extension behavior, and specifically does not render snippet references via SnippetReferenceFilter, even if the ID is valid.

Example 694
This personal snippet ID reference is not filtered: $99999
<p>This personal snippet ID reference is not filtered: $99999</p>

preview_markdown exercising project wikis API endpoint and WikiLinkFilter:

Example 695
[project-wikis-test-file](project-wikis-test-file)
<p><a href="project-wikis-test-file">project-wikis-test-file</a></p>

preview_markdown exercising group wikis API endpoint and WikiLinkFilter. This example also requires an EE license enabling the group_wikis feature:

Example 696
[group-wikis-test-file](group-wikis-test-file)
<p><a href="group-wikis-test-file">group-wikis-test-file</a></p>

Migrated golden master examples

attachment_image_for_group

Example 697
![test-file](/uploads/aa45a38ec2cfe97433281b10bbff042c/test-file.png)
TODO: Write canonical HTML for this example

attachment_image_for_project

Example 698
![test-file](/uploads/aa45a38ec2cfe97433281b10bbff042c/test-file.png)
TODO: Write canonical HTML for this example

attachment_image_for_project_wiki

Example 699
![test-file](test-file.png)
TODO: Write canonical HTML for this example

attachment_link_for_group

Example 700
[test-file](/uploads/aa45a38ec2cfe97433281b10bbff042c/test-file.zip)
TODO: Write canonical HTML for this example

attachment_link_for_project

Example 701
[test-file](/uploads/aa45a38ec2cfe97433281b10bbff042c/test-file.zip)
TODO: Write canonical HTML for this example

attachment_link_for_project_wiki

Example 702
[test-file](test-file.zip)
TODO: Write canonical HTML for this example

attachment_link_for_group_wiki

Example 703
[test-file](test-file.zip)
TODO: Write canonical HTML for this example

audio

Example 704
![Sample Audio](https://gitlab.com/gitlab.mp3)
TODO: Write canonical HTML for this example

audio_and_video_in_lists

Example 705
* ![Sample Audio](https://gitlab.com/1.mp3)
* ![Sample Video](https://gitlab.com/2.mp4)

1. ![Sample Video](https://gitlab.com/1.mp4)
2. ![Sample Audio](https://gitlab.com/2.mp3)

* [x] ![Sample Audio](https://gitlab.com/1.mp3)
* [x] ![Sample Audio](https://gitlab.com/2.mp3)
* [x] ![Sample Video](https://gitlab.com/3.mp4)
TODO: Write canonical HTML for this example

blockquote

Example 706
> This is a blockquote
>
> This is another one
TODO: Write canonical HTML for this example

bold

Example 707
**bold**
TODO: Write canonical HTML for this example

bullet_list_style_1

Example 708
* list item 1
* list item 2
  * embedded list item 3
TODO: Write canonical HTML for this example

bullet_list_style_2

Example 709
- list item 1
- list item 2
  * embedded list item 3
TODO: Write canonical HTML for this example

bullet_list_style_3

Example 710
+ list item 1
+ list item 2
  - embedded list item 3
TODO: Write canonical HTML for this example

code_block_javascript

Example 711
```javascript
  console.log('hello world')
```
TODO: Write canonical HTML for this example

code_block_plaintext

Example 712
```
  plaintext
```
TODO: Write canonical HTML for this example

code_block_unknown

Example 713
```foobar
  custom_language = >> this <<
```
TODO: Write canonical HTML for this example

color_chips

Example 714
- `#F00`
- `#F00A`
- `#FF0000`
- `#FF0000AA`
- `RGB(0,255,0)`
- `RGB(0%,100%,0%)`
- `RGBA(0,255,0,0.3)`
- `HSL(540,70%,50%)`
- `HSLA(540,70%,50%,0.3)`
TODO: Write canonical HTML for this example

description_list

Example 715
<dl>
<dt>Frog</dt>
<dd>Wet green thing</dd>
<dt>Rabbit</dt>
<dd>Warm fluffy thing</dd>
<dt>Punt</dt>
<dd>Kick a ball</dd>
<dd>Take a bet</dd>
<dt>Color</dt>
<dt>Colour</dt>
<dd>

Any hue except _white_ or **black**

</dd>
</dl>
TODO: Write canonical HTML for this example

details

Example 716
<details>
<summary>This is the visible summary of the collapsible section</summary>

1. collapsed markdown
2. more collapsed markdown

</details>
TODO: Write canonical HTML for this example

diagram_kroki_nomnoml

Example 717
```nomnoml
  #stroke: #a86128
  [<frame>Decorator pattern|
    [<abstract>Component||+ operation()]
    [Client] depends --> [Component]
    [Decorator|- next: Component]
    [Decorator] decorates -- [ConcreteComponent]
    [Component] <:- [Decorator]
    [Component] <:- [ConcreteComponent]
  ]
```
TODO: Write canonical HTML for this example

diagram_plantuml

Example 718
```plantuml
  Alice -> Bob: Authentication Request
  Bob --> Alice: Authentication Response

  Alice -> Bob: Another authentication Request
  Alice <-- Bob: Another authentication Response
```
TODO: Write canonical HTML for this example

diagram_plantuml_unicode

Example 719
```plantuml
A -> B : Text with norwegian characters: æøå
```
TODO: Write canonical HTML for this example

div

Example 720
<div>plain text</div>
<div>

just a plain ol' div, not much to _expect_!

</div>
TODO: Write canonical HTML for this example

emoji

Example 721
:sparkles: :heart: :100:
TODO: Write canonical HTML for this example

emphasis

Example 722
_emphasized text_
TODO: Write canonical HTML for this example

figure

Example 723
<figure>

![Elephant at sunset](elephant-sunset.jpg)

<figcaption>An elephant at sunset</figcaption>
</figure>
<figure>

![A crocodile wearing crocs](croc-crocs.jpg)

<figcaption>

A crocodile wearing _crocs_!

</figcaption>
</figure>
TODO: Write canonical HTML for this example

footnotes

Example 724
A footnote reference tag looks like this: [^1]

This reference tag is a mix of letters and numbers. [^footnote]

[^1]: This is the text inside a footnote.

[^footnote]: This is another footnote.
TODO: Write canonical HTML for this example

frontmatter_json

Example 725
;;;
{
  "title": "Page title"
}
;;;
TODO: Write canonical HTML for this example

frontmatter_toml

Example 726
+++
title = "Page title"
+++
TODO: Write canonical HTML for this example

frontmatter_yaml

Example 727
---
title: Page title
---
TODO: Write canonical HTML for this example

hard_break

Example 728
This is a line after a\
hard break
TODO: Write canonical HTML for this example

headings

Example 729
# Heading 1

## Heading 2

### Heading 3

#### Heading 4

##### Heading 5

###### Heading 6
TODO: Write canonical HTML for this example

horizontal_rule

Example 730
---
TODO: Write canonical HTML for this example

html_marks

Example 731
* Content editor is ~~great~~<ins>amazing</ins>.
* If the changes <abbr title="Looks good to merge">LGTM</abbr>, please <abbr title="Merge when pipeline succeeds">MWPS</abbr>.
* The English song <q>Oh I do like to be beside the seaside</q> looks like this in Hebrew: <span dir="rtl">אה, אני אוהב להיות ליד חוף הים</span>. In the computer's memory, this is stored as <bdo dir="ltr">אה, אני אוהב להיות ליד חוף הים</bdo>.
* <cite>The Scream</cite> by Edvard Munch. Painted in 1893.
* <dfn>HTML</dfn> is the standard markup language for creating web pages.
* Do not forget to buy <mark>milk</mark> today.
* This is a paragraph and <small>smaller text goes here</small>.
* The concert starts at <time datetime="20:00">20:00</time> and you'll be able to enjoy the band for at least <time datetime="PT2H30M">2h 30m</time>.
* Press <kbd>Ctrl</kbd> + <kbd>C</kbd> to copy text (Windows).
* WWF's goal is to: <q>Build a future where people live in harmony with nature.</q> We hope they succeed.
* The error occurred was: <samp>Keyboard not found. Press F1 to continue.</samp>
* The area of a triangle is: 1/2 x <var>b</var> x <var>h</var>, where <var>b</var> is the base, and <var>h</var> is the vertical height.
* <ruby>漢<rt>ㄏㄢˋ</rt></ruby>
* C<sub>7</sub>H<sub>16</sub> + O<sub>2</sub> → CO<sub>2</sub> + H<sub>2</sub>O
* The **Pythagorean theorem** is often expressed as <var>a<sup>2</sup></var> + <var>b<sup>2</sup></var> = <var>c<sup>2</sup></var>
TODO: Write canonical HTML for this example

image

Example 732
![alt text](https://gitlab.com/logo.png)
TODO: Write canonical HTML for this example

inline_code

Example 733
`code`
TODO: Write canonical HTML for this example

inline_diff

Example 734
* {-deleted-}
* {+added+}
TODO: Write canonical HTML for this example

label

Example 735
~bug
TODO: Write canonical HTML for this example

link

Example 736
[GitLab](https://gitlab.com)
TODO: Write canonical HTML for this example

math

Example 737
This math is inline $`a^2+b^2=c^2`$.

This is on a separate line:

```math
a^2+b^2=c^2
```
TODO: Write canonical HTML for this example

ordered_list

Example 738
1. list item 1
2. list item 2
3. list item 3
TODO: Write canonical HTML for this example

ordered_list_with_start_order

Example 739
134. list item 1
135. list item 2
136. list item 3
TODO: Write canonical HTML for this example

ordered_task_list

Example 740
1. [x] hello
2. [x] world
3. [ ] example
   1. [ ] of nested
      1. [x] task list
      2. [ ] items
TODO: Write canonical HTML for this example

ordered_task_list_with_order

Example 741
4893. [x] hello
4894. [x] world
4895. [ ] example
TODO: Write canonical HTML for this example

reference_for_project_wiki

Example 742
Hi @gfm_user - thank you for reporting this ~"UX bug" (#1) we hope to fix it in %1.1 as part of !1
TODO: Write canonical HTML for this example

strike

Example 743
~~del~~
TODO: Write canonical HTML for this example

table

Example 744
| header | header |
|--------|--------|
| `code` | cell with **bold** |
| ~~strike~~ | cell with _italic_ |

# content after table
TODO: Write canonical HTML for this example

table_of_contents

Example 745
[[_TOC_]]

# Lorem

Well, that's just like... your opinion.. man.

## Ipsum

### Dolar

# Sit amit

### I don't know
TODO: Write canonical HTML for this example

task_list

Example 746
* [x] hello
* [x] world
* [ ] example
  * [ ] of nested
    * [x] task list
    * [ ] items
TODO: Write canonical HTML for this example

video

Example 747
![Sample Video](https://gitlab.com/gitlab.mp4)
TODO: Write canonical HTML for this example

word_break

Example 748
Fernstraßen<wbr>bau<wbr>privat<wbr>finanzierungs<wbr>gesetz
TODO: Write canonical HTML for this example

Image Attributes

See Change the image dimensions in the GitLab Flavored Markdown documentation.

The width and height attributes for an image can be specified directly after the image markdown.

General syntax conforms to the commonmark-hs attribute syntax where it makes sense.

Example 749
![](https://gitlab.com/logo.png){width="100" height="100"}
<p><img src="https://gitlab.com/logo.png" width="100" height="100"></p>

% and px units may also be specified.

Example 750
![](https://gitlab.com/logo.png){width="100%"}
<p><img src="https://gitlab.com/logo.png" width="100%"></p>
Example 751
![](https://gitlab.com/logo.png){height="100px"}
<p><img src="https://gitlab.com/logo.png" height="100px"></p>

Whitespace is tolerated around the delimiters:

Example 752
![](https://gitlab.com/logo.png){ width="100" height="100" }
<p><img src="https://gitlab.com/logo.png" width="100" height="100"></p>

Attributes must immediately follow the image markdown.

Example 753
![](https://gitlab.com/logo.png) {width="100" height="100"}
<p><img src="https://gitlab.com/logo.png"> {width="100" height="100"}</p>

Footnotes

See the footnotes section of the user-facing documentation for GitLab Flavored Markdown.

Example 754
footnote reference tag [^fortytwo]

[^fortytwo]: footnote text
<p>
footnote reference tag
<sup>
<a href="#fn-fortytwo-42" id="fnref-fortytwo-42" data-footnote-ref>
1
</a>
</sup>
</p>
<section data-footnotes>
<ol>
<li id="fn-fortytwo-42">
<p>
footnote text
<a href="#fnref-fortytwo-42" data-footnote-backref>
</a>
</p>
</li>
</ol>
</section>