CommonMark Spec

Version 1 (2014-09-06)

John MacFarlane

1 Introduction
2 Preprocessing
3 Blocks and inlines
- 3.1 Precedence
- 3.2 Container blocks and leaf blocks
4 Leaf blocks
5 Container blocks
6 Inlines
7 Extensions
- 7.1 Attributes
Appendix A: A parsing strategy

1 Introduction

1.1 What is Markdown?

Markdown is a plain text format for writing structured documents, based on conventions used for indicating formatting in email and usenet posts. It was developed in 2004 by John Gruber, who wrote the first Markdown-to-HTML converter in perl, and it soon became widely used in websites. By 2014 there were dozens of implementations in many languages. Some of them extended basic Markdown syntax with conventions for footnotes, definition lists, tables, and other constructs, and some allowed output not just in HTML but in LaTeX and many other formats.

1.2 Why is a spec needed?

John Gruber’s canonical description of Markdown’s syntax does not specify the syntax unambiguously. Here are some examples of questions it does not answer:

How much indentation is needed for a sublist? The spec says that continuation paragraphs need to be indented four spaces, but is not fully explicit about sublists. It is natural to think that they, too, must be indented four spaces, but Markdown.pl does not require that. This is hardly a “corner case,” and divergences between implementations on this issue often lead to surprises for users in real documents. (See this comment by John Gruber.)
Is a blank line needed before a block quote or header? Most implementations do not require the blank line. However, this can lead to unexpected results in hard-wrapped text, and also to ambiguities in parsing (note that some implementations put the header inside the blockquote, while others do not). (John Gruber has also spoken in favor of requiring the blank lines.)
Is a blank line needed before an indented code block? (Markdown.pl requires it, but this is not mentioned in the documentation, and some implementations do not require it.)
```
paragraph
    code?
```
What is the exact rule for determining when list items get wrapped in <p> tags? Can a list be partially “loose” and partially “tight”? What should we do with a list like this?
```
1. one

2. two
3. three
```
Or this?
```
1.  one
    - a

    - b
2.  two
```
(There are some relevant comments by John Gruber here.)
Can list markers be indented? Can ordered list markers be right-aligned?
```
 8. item 1
 9. item 2
10. item 2a
```
Is this one list with a horizontal rule in its second item, or two lists separated by a horizontal rule?
```
* a
* * * * *
* b
```
When list markers change from numbers to bullets, do we have two lists or one? (The Markdown syntax description suggests two, but the perl scripts and many other implementations produce one.)
```
1. fee
2. fie
-  foe
-  fum
```
What are the precedence rules for the markers of inline structure? For example, is the following a valid link, or does the code span take precedence ?
```
[a backtick (`)](/url) and [another backtick (`)](/url).
```
What are the precedence rules for markers of emphasis and strong emphasis? For example, how should the following be parsed?
```
*foo *bar* baz*
```
What are the precedence rules between block-level and inline-level structure? For example, how should the following be parsed?
```
- `a long code span can contain a hyphen like this
  - and it can screw things up`
```
Can list items include headers? (Markdown.pl does not allow this, but headers can occur in blockquotes.)
```
- # Heading
```
Can link references be defined inside block quotes or list items?
```
> Blockquote [foo].
>
> [foo]: /url
```
If there are multiple definitions for the same reference, which takes precedence?
```
[foo]: /url1
[foo]: /url2

[foo][]
```

In the absence of a spec, early implementers consulted Markdown.pl to resolve these ambiguities. But Markdown.pl was quite buggy, and gave manifestly bad results in many cases, so it was not a satisfactory replacement for a spec.

Because there is no unambiguous spec, implementations have diverged considerably. As a result, users are often surprised to find that a document that renders one way on one system (say, a github wiki) renders differently on another (say, converting to docbook using pandoc). To make matters worse, because nothing in Markdown counts as a “syntax error,” the divergence often isn’t discovered right away.

1.3 About this document

This document attempts to specify Markdown syntax unambiguously. It contains many examples with side-by-side Markdown and HTML. These are intended to double as conformance tests. An accompanying script runtests.pl can be used to run the tests against any Markdown program:

perl runtests.pl spec.txt PROGRAM

Since this document describes how Markdown is to be parsed into an abstract syntax tree, it would have made sense to use an abstract representation of the syntax tree instead of HTML. But HTML is capable of representing the structural distinctions we need to make, and the choice of HTML for the tests makes it possible to run the tests against an implementation without writing an abstract syntax tree renderer.

This document is generated from a text file, spec.txt, written in Markdown with a small extension for the side-by-side tests. The script spec2md.pl can be used to turn spec.txt into pandoc Markdown, which can then be converted into other formats.

In the examples, the → character is used to represent tabs.

2 Preprocessing

A line is a sequence of zero or more characters followed by a line ending (CR, LF, or CRLF) or by the end of file.

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.

Tabs in lines are expanded to spaces, with a tab stop of 4 characters:

Example 1

→foo→baz→→bim

<pre><code>foo baz     bim
</code></pre>

Example 2

    a→a
    ὐ→a

<pre><code>a   a
ὐ   a
</code></pre>

Line endings are replaced by newline characters (LF).

A line containing no characters, or a line containing only spaces (after tab expansion), is called a blank line.

3 Blocks and inlines

We can think of a document as a sequence of blocks —structural elements like paragraphs, block quotations, lists, headers, rules, and code blocks. Blocks can contain other blocks, or they can contain inline content: words, spaces, links, emphasized text, images, and inline code.

3.1 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 3

- `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, headers, 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.

3.2 Container blocks and leaf blocks

We can divide blocks into two types: container blocks, which can contain other blocks, and leaf blocks, which cannot.

4 Leaf blocks

This section describes the different kinds of leaf block that make up a Markdown document.

4.1 Horizontal rules

A line consisting of 0-3 spaces of indentation, followed by a sequence of three or more matching -, _, or * characters, each followed optionally by any number of spaces, forms a horizontal rule.

Example 4

***
---
___

<hr />
<hr />
<hr />

Wrong characters:

Example 5

+++

<p>+++</p>

Example 6

===

<p>===</p>

Not enough characters:

Example 7

--
**
__

<p>--
**
__</p>

One to three spaces indent are allowed:

Example 8

 ***
  ***
   ***

<hr />
<hr />
<hr />

Four spaces is too many:

Example 9

***

<pre><code>***
</code></pre>

Example 10

Foo
    ***

<p>Foo
***</p>

More than three characters may be used:

Example 11

_____________________________________

<hr />

Spaces are allowed between the characters:

Example 12

 - - -

<hr />

Example 13

 **  * ** * ** * **

<hr />

Example 14

-     -      -      -

<hr />

Spaces are allowed at the end:

Example 15

- - - -

<hr />

However, no other characters may occur at the end or the beginning:

Example 16

_ _ _ _ a

a------

<p>_ _ _ _ a</p>
<p>a------</p>

It is required that all of the non-space characters be the same. So, this is not a horizontal rule:

Example 17

*-*

<p><em>-</em></p>

Horizontal rules do not need blank lines before or after:

Example 18

- foo
***
- bar

<ul>
<li>foo</li>
</ul>
<hr />
<ul>
<li>bar</li>
</ul>

Horizontal rules can interrupt a paragraph:

Example 19

Foo
***
bar

<p>Foo</p>
<hr />
<p>bar</p>

Note, however, that this is a setext header, not a paragraph followed by a horizontal rule:

Example 20

Foo
---
bar

<h2>Foo</h2>
<p>bar</p>

When both a horizontal rule and a list item are possible interpretations of a line, the horizontal rule is preferred:

Example 21

* Foo
* * *
* Bar

<ul>
<li>Foo</li>
</ul>
<hr />
<ul>
<li>Bar</li>
</ul>

If you want a horizontal rule in a list item, use a different bullet:

Example 22

- Foo
- * * *

<ul>
<li>Foo</li>
<li><hr /></li>
</ul>

4.2 ATX headers

An ATX header 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 # characters. The opening sequence of # characters cannot be followed directly by a non-space character. The closing # characters may be followed by spaces only. The opening # character may be indented 0-3 spaces. The raw contents of the header are stripped of leading and trailing spaces before being parsed as inline content. The header level is equal to the number of # characters in the opening sequence.

Simple headers:

Example 23

# 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 header:

Example 24

####### foo

<p>####### foo</p>

A space is required between the # characters and the header’s contents. 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 headers:

Example 25

#5 bolt

<p>#5 bolt</p>

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

Example 26

\## foo

<p>## foo</p>

Contents are parsed as inlines:

Example 27

# foo *bar* \*baz\*

<h1>foo <em>bar</em> *baz*</h1>

Leading and trailing blanks are ignored in parsing inline content:

Example 28

#                  foo

<h1>foo</h1>

One to three spaces indentation are allowed:

Example 29

 ### foo
  ## foo
   # foo

<h3>foo</h3>
<h2>foo</h2>
<h1>foo</h1>

Four spaces are too much:

Example 30

    # foo

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

Example 31

foo
    # bar

<p>foo
# bar</p>

A closing sequence of # characters is optional:

Example 32

## foo ##
  ###   bar    ###

<h2>foo</h2>
<h3>bar</h3>

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

Example 33

# foo ##################################
##### foo ##

<h1>foo</h1>
<h5>foo</h5>

Spaces are allowed after the closing sequence:

Example 34

### foo ###

<h3>foo</h3>

A sequence of # characters with a non-space character following it is not a closing sequence, but counts as part of the contents of the header:

Example 35

### foo ### b

<h3>foo ### b</h3>

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

Example 36

### foo \###
## foo \#\##
# foo \#

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

ATX headers need not be separated from surrounding content by blank lines, and they can interrupt paragraphs:

Example 37

****
## foo
****

<hr />
<h2>foo</h2>
<hr />

Example 38

Foo bar
# baz
Bar foo

<p>Foo bar</p>
<h1>baz</h1>
<p>Bar foo</p>

ATX headers can be empty:

Example 39

## 
#
### ###

<h2></h2>
<h1></h1>
<h3></h3>

4.3 Setext headers

A setext header consists of a line of text, containing at least one non-space character, with no more than 3 spaces indentation, followed by a setext header underline. A setext header underline is a sequence of = characters or a sequence of - characters, with no more than 3 spaces indentation and any number of trailing spaces. The header is a level 1 header if = characters are used, and a level 2 header if - characters are used. The contents of the header are the result of parsing the first line as Markdown inline content.

In general, a setext header need not be preceded or followed by a blank line. However, it cannot interrupt a paragraph, so when a setext header comes after a paragraph, a blank line is needed between them.

Simple examples:

Example 40

Foo *bar*
=========

Foo *bar*
---------

<h1>Foo <em>bar</em></h1>
<h2>Foo <em>bar</em></h2>

The underlining can be any length:

Example 41

Foo
-------------------------

Foo
=

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

The header content can be indented up to three spaces, and need not line up with the underlining:

Example 42

   Foo
---

  Foo
-----

  Foo
  ===

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

Four spaces indent is too much:

Example 43

    Foo
    ---

    Foo
---

<pre><code>Foo
---

Foo
</code></pre>
<hr />

The setext header underline can be indented up to three spaces, and may have trailing spaces:

Example 44

Foo
   ----

<h2>Foo</h2>

Four spaces is too much:

Example 45

Foo
     ---

<p>Foo
---</p>

The setext header underline cannot contain internal spaces:

Example 46

Foo
= =

Foo
--- -

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

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

Example 47

Foo  
-----

<h2>Foo</h2>

Nor does a backslash at the end:

Example 48

Foo\
----

<h2>Foo\</h2>

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

Example 49

`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 header underline cannot be a lazy line:

Example 50

> Foo
---

<blockquote>
<p>Foo</p>
</blockquote>
<hr />

A setext header cannot interrupt a paragraph:

Example 51

Foo
Bar
---

Foo
Bar
===

<p>Foo
Bar</p>
<hr />
<p>Foo
Bar
===</p>

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

Example 52

---
Foo
---
Bar
---
Baz

<hr />
<h2>Foo</h2>
<h2>Bar</h2>
<p>Baz</p>

Setext headers cannot be empty:

Example 53


====

<p>====</p>

4.4 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. An indented code block cannot interrupt a paragraph, so if it occurs before or after a paragraph, there must be an intervening blank line. The contents of the code block are the literal contents of the lines, including trailing newlines, minus four spaces of indentation. An indented code block has no attributes.

Example 54

    a simple
      indented code block

<pre><code>a simple
  indented code block
</code></pre>

The contents are literal text, and do not get parsed as Markdown:

Example 55

    <a/>
    *hi*

    - one

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

- one
</code></pre>

Here we have three chunks separated by blank lines:

Example 56

    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 57

    chunk1
      
      chunk2

<pre><code>chunk1
  
  chunk2
</code></pre>

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

Example 58

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 59

    foo
bar

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

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

Example 60

# Header
    foo
Header
------
    foo
----

<h1>Header</h1>
<pre><code>foo
</code></pre>
<h2>Header</h2>
<pre><code>foo
</code></pre>
<hr />

The first line can be indented more than four spaces:

Example 61

        foo
    bar

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

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

Example 62

foo

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

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

Example 63

foo

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

4.5 Fenced code blocks

A code fence is a sequence of at least three consecutive backtick characters (`) or tildes (~). (Tildes and backticks cannot be mixed.) A fenced code block begins with a code fence, indented no more than three spaces.

The line with the opening code fence may optionally contain some text following the code fence; this is trimmed of leading and trailing spaces and called the info string. The info string may not contain any backtick characters. (The reason for this restriction is that otherwise some inline code would be incorrectly interpreted as the beginning of a fenced code block.)

The content of the code block consists of all subsequent lines, until a closing code fence of the same type as the code block began with (backticks or tildes), and with at least as many backticks or tildes as the opening code fence. If the leading code fence is indented N spaces, then up to N spaces of indentation are removed from each line of the content (if present). (If a content line is not indented, it is preserved unchanged. If it is indented less than N spaces, all of the indentation is removed.)

The closing code fence may be indented up to three spaces, and may be followed only by spaces, which are ignored. If the end of the containing block (or document) is reached and no closing code fence has been found, the code block contains all of the lines after the opening code fence until the end of the containing block (or document). (An alternative spec would require backtracking in the event that a closing code fence is not found. But this makes parsing much less efficient, and there seems to be no real down side to the behavior described here.)

A fenced code block may interrupt a paragraph, and does not require a blank line either before or after.

The content of a code fence is treated as literal text, not parsed as inlines. The first word of the info string is typically used to specify the language of the code sample, and rendered in the class attribute of the code tag. However, this spec does not mandate any particular treatment of the info string.

Here is a simple example with backticks:

Example 64

```
<
 >
```

<pre><code>&lt;
 &gt;
</code></pre>

With tildes:

Example 65

~~~
<
 >
~~~

<pre><code>&lt;
 &gt;
</code></pre>

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

Example 66

```
aaa
~~~
```

<pre><code>aaa
~~~
</code></pre>

Example 67

~~~
aaa
```
~~~

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

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

Example 68

````
aaa
```
``````

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

Example 69

~~~~
aaa
~~~
~~~~

<pre><code>aaa
~~~
</code></pre>

Unclosed code blocks are closed by the end of the document:

Example 70

```

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

Example 71

`````

```
aaa

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

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

Example 72

```

  
```

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

A code block can be empty:

Example 73

```
```

<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 74

 ```
 aaa
aaa
```

<pre><code>aaa
aaa
</code></pre>

Example 75

  ```
aaa
  aaa
aaa
  ```

<pre><code>aaa
aaa
aaa
</code></pre>

Example 76

   ```
   aaa
    aaa
  aaa
   ```

<pre><code>aaa
 aaa
aaa
</code></pre>

Four spaces indentation produces an indented code block:

Example 77

    ```
    aaa
    ```

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

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

Example 78

``` ```
aaa

<p><code></code>
aaa</p>

Example 79

~~~~~~
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 80

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 81

foo
---
~~~
bar
~~~
# baz

<h2>foo</h2>
<pre><code>bar
</code></pre>
<h1>baz</h1>

An info string can be provided after the opening code fence. Opening and closing spaces will be stripped, and the first word, prefixed with language-, is used as the value for the class attribute of the code element within the enclosing pre element.

Example 82

```ruby
def foo(x)
  return 3
end
```

<pre><code class="language-ruby">def foo(x)
  return 3
end
</code></pre>

Example 83

~~~~    ruby startline=3 $%@#$
def foo(x)
  return 3
end
~~~~~~~

<pre><code class="language-ruby">def foo(x)
  return 3
end
</code></pre>

Example 84

````;
````

<pre><code class="language-;"></code></pre>

Info strings for backtick code blocks cannot contain backticks:

Example 85

``` aa ```
foo

<p><code>aa</code>
foo</p>

Closing code fences cannot have info strings:

Example 86

```
``` aaa
```

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

4.6 HTML blocks

An HTML block tag is an open tag or closing tag whose tag name is one of the following (case-insensitive): article, header, aside, hgroup, blockquote, hr, iframe, body, li, map, button, object, canvas, ol, caption, output, col, p, colgroup, pre, dd, progress, div, section, dl, table, td, dt, tbody, embed, textarea, fieldset, tfoot, figcaption, th, figure, thead, footer, footer, tr, form, ul, h1, h2, h3, h4, h5, h6, video, script, style.

An HTML block begins with an HTML block tag, HTML comment, processing instruction, declaration, or CDATA section. It ends when a blank line or the end of the input is encountered. The initial line may be indented up to three spaces, and subsequent lines may have any indentation. The contents of the HTML block are interpreted as raw HTML, and will not be escaped in HTML output.

Some simple examples:

Example 87

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

okay.

<table>
  <tr>
    <td>
           hi
    </td>
  </tr>
</table>
<p>okay.</p>

Example 88

 <div>
  *hello*
         <foo><a>

 <div>
  *hello*
         <foo><a>

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

Example 89

<DIV CLASS="foo">

*Markdown*

</DIV>

<DIV CLASS="foo">
<p><em>Markdown</em></p>
</DIV>

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 90

<div></div>
``` c
int x = 33;
```

<div></div>
``` c
int x = 33;
```

A comment:

Example 91

<!-- Foo
bar
   baz -->

<!-- Foo
bar
   baz -->

A processing instruction:

Example 92

<?php
  echo 'foo'
?>

<?php
  echo 'foo'
?>

CDATA:

Example 93

<![CDATA[
function matchwo(a,b)
{
if (a < b && a < 0) then
  {
  return 1;
  }
else
  {
  return 0;
  }
}
]]>

<![CDATA[
function matchwo(a,b)
{
if (a < b && a < 0) then
  {
  return 1;
  }
else
  {
  return 0;
  }
}
]]>

The opening tag can be indented 1-3 spaces, but not 4:

Example 94

  <!-- foo -->

    <!-- foo -->

  <!-- foo -->
<pre><code>&lt;!-- foo --&gt;
</code></pre>

An HTML block can interrupt a paragraph, and need not be preceded by a blank line.

Example 95

Foo
<div>
bar
</div>

<p>Foo</p>
<div>
bar
</div>

However, a following blank line is always needed, except at the end of a document:

Example 96

<div>
bar
</div>
*foo*

<div>
bar
</div>
*foo*

An incomplete HTML block tag may also start an HTML block:

Example 97

<div class
foo

<div class
foo

This rule differs from John Gruber’s original Markdown syntax specification, which says:

The only restrictions are that block-level HTML elements — e.g. <div>, <table>, <pre>, <p>, etc. — must be separated from surrounding content by blank lines, and the start and end tags of the block should not be indented with tabs or spaces.

In some ways Gruber’s rule is more restrictive than the one given here:

It requires that an HTML block be preceded by a blank line.
It does not allow the start tag to be indented.
It requires a matching end tag, which it also does not allow to be indented.

Indeed, most Markdown implementations, including some of Gruber’s own perl implementations, do not impose 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:

Example 98

<div>

*Emphasized* text.

</div>

<div>
<p><em>Emphasized</em> text.</p>
</div>

Compare:

Example 99

<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 100

<table>

<tr>

<td>
Hi
</td>

</tr>

</table>

<table>
<tr>
<td>
Hi
</td>
</tr>
</table>

Moreover, blank lines are usually not necessary and can be deleted. The exception is inside <pre> tags; here, one can replace the blank lines with 
 entities.

So there is no important loss of expressive power with the new rule.

4.7 Link reference definitions

A link reference definition consists of a link label, indented up to three spaces, followed by a colon (:), optional blank space (including up to one newline), a link destination, optional blank space (including up to one newline), and an optional link title, which if it is present must be separated from the link destination by whitespace. No further non-space 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 101

[foo]: /url "title"

[foo]

<p><a href="/url" title="title">foo</a></p>

Example 102

   [foo]: 
      /url  
           'the title'  

[foo]

<p><a href="/url" title="the title">foo</a></p>

Example 103

[Foo*bar\]]:my_(url) 'title (with parens)'

[Foo*bar\]]

<p><a href="my_(url)" title="title (with parens)">Foo*bar]</a></p>

Example 104

[Foo bar]:
<my url>
'title'

[Foo bar]

<p><a href="my url" title="title">Foo bar</a></p>

The title may be omitted:

Example 105

[foo]:
/url

[foo]

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

The link destination may not be omitted:

Example 106

[foo]:

[foo]

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

A link can come before its corresponding definition:

Example 107

[foo]

[foo]: url

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

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

Example 108

[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 109

[FOO]: /url

[Foo]

<p><a href="/url">Foo</a></p>

Example 110

[ΑΓΩ]: /φου

[αγω]

<p><a href="/φου">αγω</a></p>

Here is a link reference definition with no corresponding link. It contributes nothing to the document.

Example 111

[foo]: /url

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

Example 112

[foo]: /url "title" ok

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

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

Example 113

    [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 114

```
[foo]: /url
```

[foo]

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

A link reference definition cannot interrupt a paragraph.

Example 115

Foo
[bar]: /baz

[bar]

<p>Foo
[bar]: /baz</p>
<p>[bar]</p>

However, it can directly follow other block elements, such as headers and horizontal rules, and it need not be followed by a blank line.

Example 116

# [Foo]
[foo]: /url
> bar

<h1><a href="/url">Foo</a></h1>
<blockquote>
<p>bar</p>
</blockquote>

Several link references can occur one after another, without intervening blank lines.

Example 117

[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 118

[foo]

> [foo]: /url

<p><a href="/url">foo</a></p>
<blockquote>
</blockquote>

4.8 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 spaces.

A simple example with two paragraphs:

Example 119

aaa

bbb

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

Paragraphs can contain multiple lines, but no blank lines:

Example 120

aaa
bbb

ccc
ddd

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

Multiple blank lines between paragraph have no effect:

Example 121

aaa


bbb

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

Leading spaces are skipped:

Example 122

  aaa
 bbb

<p>aaa
bbb</p>

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

Example 123

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 124

   aaa
bbb

<p>aaa
bbb</p>

Example 125

    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 126

aaa     
bbb

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

4.9 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 127

  

aaa
  

# aaa

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

5 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].)

5.1 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:

Basic case. If a string of lines Ls constitute a sequence of blocks Bs, then the result of appending a [block quote marker] to the beginning of each line in Ls is a block quote containing Bs.
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-space 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.
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 128

> # Foo
> bar
> baz

<blockquote>
<h1>Foo</h1>
<p>bar
baz</p>
</blockquote>

The spaces after the > characters can be omitted:

Example 129

># Foo
>bar
> baz

<blockquote>
<h1>Foo</h1>
<p>bar
baz</p>
</blockquote>

The > characters can be indented 1-3 spaces:

Example 130

   > # Foo
   > bar
 > baz

<blockquote>
<h1>Foo</h1>
<p>bar
baz</p>
</blockquote>

Four spaces gives us a code block:

Example 131

    > # Foo
    > bar
    > baz

<pre><code>&gt; # Foo
&gt; bar
&gt; baz
</code></pre>

The Laziness clause allows us to omit the > before a paragraph continuation line:

Example 132

> # 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 133

> bar
baz
> foo

<blockquote>
<p>bar
baz
foo</p>
</blockquote>

Laziness only applies to lines that are continuations of paragraphs. Lines containing characters or indentation that indicate block structure cannot be lazy.

Example 134

> foo
---

<blockquote>
<p>foo</p>
</blockquote>
<hr />

Example 135

> - foo
- bar

<blockquote>
<ul>
<li>foo</li>
</ul>
</blockquote>
<ul>
<li>bar</li>
</ul>

Example 136

>     foo
    bar

<blockquote>
<pre><code>foo
</code></pre>
</blockquote>
<pre><code>bar
</code></pre>

Example 137

> ```
foo
```

<blockquote>
<pre><code></code></pre>
</blockquote>
<p>foo</p>
<pre><code></code></pre>

A block quote can be empty:

Example 138

<blockquote>
</blockquote>

Example 139

>
>  
>

<blockquote>
</blockquote>

A block quote can have initial or final blank lines:

Example 140

>
> foo
>

<blockquote>
<p>foo</p>
</blockquote>

A blank line always separates block quotes:

Example 141

> 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 142

> foo
> bar

<blockquote>
<p>foo
bar</p>
</blockquote>

To get a block quote with two paragraphs, use:

Example 143

> foo
>
> bar

<blockquote>
<p>foo</p>
<p>bar</p>
</blockquote>

Block quotes can interrupt paragraphs:

Example 144

foo
> bar

<p>foo</p>
<blockquote>
<p>bar</p>
</blockquote>

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

Example 145

> 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 146

> bar
baz

<blockquote>
<p>bar
baz</p>
</blockquote>

Example 147

> bar

baz

<blockquote>
<p>bar</p>
</blockquote>
<p>baz</p>

Example 148

> 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 149

> > > foo
bar

<blockquote>
<blockquote>
<blockquote>
<p>foo
bar</p>
</blockquote>
</blockquote>
</blockquote>

Example 150

>>> 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 151

>     code

>    not code

<blockquote>
<pre><code>code
</code></pre>
</blockquote>
<blockquote>
<p>not code</p>
</blockquote>

5.2 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 one of more digits (0-9), followed by either a . character or a ) character.

The following rules define list items:

Basic case. If a sequence of lines Ls constitute a sequence of blocks Bs starting with a non-space character and not separated from each other by more than one blank line, and M is a list marker M of width W followed by 0 < N < 5 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.

For example, let Ls be the lines

Example 152

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 153

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-space 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 154

- one

 two

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

Example 155

- one

  two

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

Example 156

 -    one

     two

<ul>
<li>one</li>
</ul>
<pre><code> two
</code></pre>

Example 157

 -    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-space 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 158

   > > 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 159

>>- one
>>
  >  > two

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

A list item may not contain blocks that are separated by more than one blank line. Thus, two blank lines will end a list, unless the two blanks are contained in a fenced code block.

Example 160

- foo

  bar

- foo


  bar

- ```
  foo


  bar
  ```

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


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

A list item may contain any kind of block:

Example 161

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>

Item starting with indented code. If a sequence of lines Ls constitute a sequence of blocks Bs starting with an indented code block and not separated from each other by more than one blank line, and M is a list marker M 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 162

- foo

      bar

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

And in this case it is 11 spaces:

Example 163

  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 164

    indented code

paragraph

    more code

<pre><code>indented code
</code></pre>
<p>paragraph</p>
<pre><code>more code
</code></pre>

Example 165

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 166

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-space 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 167

   foo

bar

<p>foo</p>
<p>bar</p>

Example 168

-    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 169

-  foo

   bar

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

Indentation. If a sequence of lines Ls constitutes a list item according to rule #1 or #2, then the result of indenting each line of L 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 170

 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 171

  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 172

   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 173

    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>

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-space character after the indentation is paragraph continuation text is a list item with the same contents and attributes.

Here is an example with lazy continuation lines:

Example 174

  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 175

  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 176

> 1. > Blockquote
continued here.

<blockquote>
<ol>
<li><blockquote>
<p>Blockquote
continued here.</p>
</blockquote></li>
</ol>
</blockquote>

Example 177

> 1. > Blockquote
> continued here.

<blockquote>
<ol>
<li><blockquote>
<p>Blockquote
continued here.</p>
</blockquote></li>
</ol>
</blockquote>

That’s all. Nothing that is not counted as a list item by rules #1–4 counts as a list item.

The rules for sublists follow from the general rules above. A sublist must be indented the same number of spaces a paragraph would need to be in order to be included in the list item.

So, in this case we need two spaces indent:

Example 178

- foo
  - bar
    - baz

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

One is not enough:

Example 179

- foo
 - bar
  - baz

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

Here we need four, because the list marker is wider:

Example 180

10) foo
    - bar

<ol start="10">
<li>foo
<ul>
<li>bar</li>
</ul></li>
</ol>

Three is not enough:

Example 181

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 182

- - foo

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

Example 183

1. - 2. foo

<ol>
<li><ul>
<li><ol start="2">
<li>foo</li>
</ol></li>
</ul></li>
</ol>

A list item may be empty:

Example 184

- foo
-
- bar

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

Example 185

<ul>
<li></li>
</ul>

5.2.1 Motivation

John Gruber’s Markdown spec says the following about list items:

“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.”
“To make lists look nice, you can wrap items with hanging indents…. But if you don’t want to, you don’t have to.”
“List items may consist of multiple paragraphs. Each subsequent paragraph in a list item must be indented by either 4 spaces or one tab.”
“It looks nice if you indent every line of the subsequent paragraphs, but here again, Markdown will allow you to be lazy.”
“To put a blockquote within a list item, the blockquote’s > delimiters need to be indented.”
“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, #4, 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

<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.

5.3 Lists

A list is a sequence of one or more list items of the same type. The list items may be separated by single blank lines, but two blank lines end all containing lists.

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 it 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 with 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 186

- foo
- bar
+ baz

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

Example 187

1. foo
2. bar
3) baz

<ol>
<li>foo</li>
<li>bar</li>
</ol>
<ol start="3">
<li>baz</li>
</ol>

There can be blank lines between items, but two blank lines end a list:

Example 188

- foo

- bar


- baz

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

As illustrated above in the section on list items, two blank lines between blocks within a list item will also end a list:

Example 189

- foo


  bar
- baz

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

Indeed, two blank lines will end all containing lists:

Example 190

- foo
  - bar
    - baz


      bim

<ul>
<li>foo
<ul>
<li>bar
<ul>
<li>baz</li>
</ul></li>
</ul></li>
</ul>
<pre><code>  bim
</code></pre>

Thus, two blank lines can be used 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:

Example 191

- foo
- bar


- baz
- bim

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

Example 192

-   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 193

- 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>

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

Example 194

- 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 195

* 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 196

- 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 197

- 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 198

- 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 inner list is loose while the other list is tight:

Example 199

- 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 200

* 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 201

- 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 202

- a

<ul>
<li>a</li>
</ul>

Example 203

- a
  - b

<ul>
<li>a
<ul>
<li>b</li>
</ul></li>
</ul>

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

Example 204

* foo
  * bar

  baz

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

Example 205

- 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>

6 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 206

`hi`lo`

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

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

6.1 Backslash escapes

Any ASCII punctuation character may be backslash-escaped:

Example 207

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

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

Backslashes before other characters are treated as literal backslashes:

Example 208

\→\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 209

\*not emphasized*
\<br/> not a tag
\[not a link](/foo)
\`not code`
1\. not a list
\* not a list
\# not a header
\[foo]: /url "not a reference"

<p>*not emphasized*
&lt;br/&gt; not a tag
[not a link](/foo)
`not code`
1. not a list
* not a list
# not a header
[foo]: /url &quot;not a reference&quot;</p>

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

Example 210

\\*emphasis*

<p>\<em>emphasis</em></p>

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

Example 211

foo\
bar

<p>foo<br />
bar</p>

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

Example 212

`` \[\` ``

<p><code>\[\`</code></p>

Example 213

    \[\]

<pre><code>\[\]
</code></pre>

Example 214

~~~
\[\]
~~~

<pre><code>\[\]
</code></pre>

Example 215

<http://google.com?find=\*>

<p><a href="http://google.com?find=\*">http://google.com?find=\*</a></p>

Example 216

<a href="/bar\/)">

<p><a href="/bar\/)"></p>

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

Example 217

[foo](/bar\* "ti\*tle")

<p><a href="/bar*" title="ti*tle">foo</a></p>

Example 218

[foo]

[foo]: /bar\* "ti\*tle"

<p><a href="/bar*" title="ti*tle">foo</a></p>

Example 219

``` foo\+bar
foo
```

<pre><code class="language-foo+bar">foo
</code></pre>

6.2 Entities

Entities are parsed as entities, not as literal text, in all contexts except code spans and code blocks. Three kinds of entities are recognized.

Named entities consist of & + a string of 2-32 alphanumerics beginning with a letter + ;.

Example 220

&nbsp; &amp; &copy; &AElig; &Dcaron; &frac34; &HilbertSpace; &DifferentialD; &ClockwiseContourIntegral;

<p>&nbsp; &amp; &copy; &AElig; &Dcaron; &frac34; &HilbertSpace; &DifferentialD; &ClockwiseContourIntegral;</p>

Decimal entities consist of &# + a string of 1–8 arabic digits + ;.

Example 221

&#1; &#35; &#1234; &#992; &#98765432;

<p>&#1; &#35; &#1234; &#992; &#98765432;</p>

Hexadecimal entities consist of &# + either X or x + a string of 1-8 hexadecimal digits + ;.

Example 222

&#x1; &#X22; &#XD06; &#xcab;

<p>&#x1; &#X22; &#XD06; &#xcab;</p>

Here are some nonentities:

Example 223

&nbsp &x; &#; &#x; &#123456789; &ThisIsWayTooLongToBeAnEntityIsntIt; &hi?;

<p>&amp;nbsp &amp;x; &amp;#; &amp;#x; &amp;#123456789; &amp;ThisIsWayTooLongToBeAnEntityIsntIt; &amp;hi?;</p>

Although HTML5 does accept some entities without a trailing semicolon (such as &copy), these are not recognized as entities here:

Example 224

&copy

<p>&amp;copy</p>

On the other hand, many strings that are not on the list of HTML5 named entities are recognized as entities here:

Example 225

&MadeUpEntity;

<p>&MadeUpEntity;</p>

Entities are recognized in any context besides code spans or code blocks, including raw HTML, URLs, link titles, and fenced code block info strings:

Example 226

<a href="&ouml;&ouml;.html">

<p><a href="&ouml;&ouml;.html"></p>

Example 227

[foo](/f&ouml;&ouml; "f&ouml;&ouml;")

<p><a href="/f&ouml;&ouml;" title="f&ouml;&ouml;">foo</a></p>

Example 228

[foo]

[foo]: /f&ouml;&ouml; "f&ouml;&ouml;"

<p><a href="/f&ouml;&ouml;" title="f&ouml;&ouml;">foo</a></p>

Example 229

``` f&ouml;&ouml;
foo
```

<pre><code class="language-f&ouml;&ouml;">foo
</code></pre>

Entities are treated as literal text in code spans and code blocks:

Example 230

`f&ouml;&ouml;`

<p><code>f&amp;ouml;&amp;ouml;</code></p>

Example 231

    f&ouml;f&ouml;

<pre><code>f&amp;ouml;f&amp;ouml;
</code></pre>

6.3 Code span

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, with leading and trailing spaces and newlines removed, and consecutive spaces and newlines collapsed to single spaces.

This is a simple code span:

Example 232

`foo`

<p><code>foo</code></p>

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

Example 233

`` foo ` bar  ``

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

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

Example 234

` `` `

<p><code>``</code></p>

Newlines are treated like spaces:

Example 235

``
foo
``

<p><code>foo</code></p>

Interior spaces and newlines are collapsed into single spaces, just as they would be by a browser:

Example 236

`foo   bar
  baz`

<p><code>foo bar baz</code></p>

Q: Why not just leave the spaces, since browsers will collapse them anyway? A: Because we might be targeting a non-HTML format, and we shouldn’t rely on HTML-specific rendering assumptions.

(Existing implementations differ in their treatment of internal spaces and newlines. Some, including Markdown.pl and showdown, convert an internal newline into a <br /> tag. But this makes things difficult for those who like to hard-wrap their paragraphs, since a line break in the midst of a code span will cause an unintended line break in the output. Others just leave internal spaces as they are, which is fine if only HTML is being targeted.)

Example 237

`foo `` bar`

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

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

Example 238

`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.

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 239

*foo`*`

<p>*foo<code>*</code></p>

And this is not parsed as a link:

Example 240

[not a `link](/foo`)

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

But this is a link:

Example 241

<http://foo.bar.`baz>`

<p><a href="http://foo.bar.`baz">http://foo.bar.`baz</a>`</p>

And this is an HTML tag:

Example 242

<a href="`">`

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

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

Example 243

```foo``

<p>```foo``</p>

Example 244

`foo

<p>`foo</p>

6.4 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 following rules capture all of these patterns, while allowing for efficient parsing strategies that do not backtrack:

A single * character can open emphasis iff
1. it is not part of a sequence of four or more unescaped *s,
2. it is not followed by whitespace, and
3. either it is not followed by a * character or it is followed immediately by strong emphasis.
A single _ character can open emphasis iff
1. it is not part of a sequence of four or more unescaped _s,
2. it is not followed by whitespace,
3. is is not preceded by an ASCII alphanumeric character, and
4. either it is not followed by a _ character or it is followed immediately by strong emphasis.
A single * character can close emphasis iff
1. it is not part of a sequence of four or more unescaped *s, and
2. it is not preceded by whitespace.
A single _ character can close emphasis iff
1. it is not part of a sequence of four or more unescaped _s,
2. it is not preceded by whitespace, and
3. it is not followed by an ASCII alphanumeric character.
A double ** can open strong emphasis iff
1. it is not part of a sequence of four or more unescaped *s,
2. it is not followed by whitespace, and
3. either it is not followed by a * character or it is followed immediately by emphasis.
A double __ can open strong emphasis iff
1. it is not part of a sequence of four or more unescaped _s,
2. it is not followed by whitespace, and
3. it is not preceded by an ASCII alphanumeric character, and
4. either it is not followed by a _ character or it is followed immediately by emphasis.
A double ** can close strong emphasis iff
1. it is not part of a sequence of four or more unescaped *s, and
2. it is not preceded by whitespace.
A double __ can close strong emphasis iff
1. it is not part of a sequence of four or more unescaped _s,
2. it is not preceded by whitespace, and
3. it is not followed by an ASCII alphanumeric character.
Emphasis begins with a delimiter that can open emphasis and includes inlines parsed sequentially until a delimiter that can close emphasis, and that uses the same character (_ or *) as the opening delimiter, is reached.
Strong emphasis begins with a delimiter that can open strong emphasis and includes inlines parsed sequentially until a delimiter that can close strong emphasis, and that uses the same character (_ or *) as the opening delimiter, is reached.

These rules can be illustrated through a series of examples.

Simple emphasis:

Example 245

*foo bar*

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

Example 246

_foo bar_

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

Simple strong emphasis:

Example 247

**foo bar**

<p><strong>foo bar</strong></p>

Example 248

__foo bar__

<p><strong>foo bar</strong></p>

Emphasis can continue over line breaks:

Example 249

*foo
bar*

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

Example 250

_foo
bar_

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

Example 251

**foo
bar**

<p><strong>foo
bar</strong></p>

Example 252

__foo
bar__

<p><strong>foo
bar</strong></p>

Emphasis can contain other inline constructs:

Example 253

*foo [bar](/url)*

<p><em>foo <a href="/url">bar</a></em></p>

Example 254

_foo [bar](/url)_

<p><em>foo <a href="/url">bar</a></em></p>

Example 255

**foo [bar](/url)**

<p><strong>foo <a href="/url">bar</a></strong></p>

Example 256

__foo [bar](/url)__

<p><strong>foo <a href="/url">bar</a></strong></p>

Symbols contained in other inline constructs will not close emphasis:

Example 257

*foo [bar*](/url)

<p>*foo <a href="/url">bar*</a></p>

Example 258

_foo [bar_](/url)

<p>_foo <a href="/url">bar_</a></p>

Example 259

**<a href="**">

<p>**<a href="**"></p>

Example 260

__<a href="__">

<p>__<a href="__"></p>

Example 261

*a `*`*

<p><em>a <code>*</code></em></p>

Example 262

_a `_`_

<p><em>a <code>_</code></em></p>

Example 263

**a<http://foo.bar?q=**>

<p>**a<a href="http://foo.bar?q=**">http://foo.bar?q=**</a></p>

Example 264

__a<http://foo.bar?q=__>

<p>__a<a href="http://foo.bar?q=__">http://foo.bar?q=__</a></p>

This is not emphasis, because the opening delimiter is followed by white space:

Example 265

and * foo bar*

<p>and * foo bar*</p>

Example 266

_ foo bar_

<p>_ foo bar_</p>

Example 267

and ** foo bar**

<p>and ** foo bar**</p>

Example 268

__ foo bar__

<p>__ foo bar__</p>

This is not emphasis, because the closing delimiter is preceded by white space:

Example 269

and *foo bar *

<p>and *foo bar *</p>

Example 270

and _foo bar _

<p>and _foo bar _</p>

Example 271

and **foo bar **

<p>and **foo bar **</p>

Example 272

and __foo bar __

<p>and __foo bar __</p>

The rules imply that a sequence of four or more unescaped * or _ characters will always be parsed as a literal string:

Example 273

****hi****

<p>****hi****</p>

Example 274

_____hi_____

<p>_____hi_____</p>

Example 275

Sign here: _________

<p>Sign here: _________</p>

The rules also imply that there can be no empty emphasis or strong emphasis:

Example 276

** is not an empty emphasis

<p>** is not an empty emphasis</p>

Example 277

**** is not an empty strong emphasis

<p>**** is not an empty strong emphasis</p>

To include * or _ in emphasized sections, use backslash escapes or code spans:

Example 278

*here is a \**

<p><em>here is a *</em></p>

Example 279

__this is a double underscore (`__`)__

<p><strong>this is a double underscore (<code>__</code>)</strong></p>

* delimiters allow intra-word emphasis; _ delimiters do not:

Example 280

foo*bar*baz

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

Example 281

foo_bar_baz

<p>foo_bar_baz</p>

Example 282

foo__bar__baz

<p>foo__bar__baz</p>

Example 283

_foo_bar_baz_

<p><em>foo_bar_baz</em></p>

Example 284

11*15*32

<p>11<em>15</em>32</p>

Example 285

11_15_32

<p>11_15_32</p>

Internal underscores will be ignored in underscore-delimited emphasis:

Example 286

_foo_bar_baz_

<p><em>foo_bar_baz</em></p>

Example 287

__foo__bar__baz__

<p><strong>foo__bar__baz</strong></p>

The rules are sufficient for the following nesting patterns:

Example 288

***foo bar***

<p><strong><em>foo bar</em></strong></p>

Example 289

___foo bar___

<p><strong><em>foo bar</em></strong></p>

Example 290

***foo** bar*

<p><em><strong>foo</strong> bar</em></p>

Example 291

___foo__ bar_

<p><em><strong>foo</strong> bar</em></p>

Example 292

***foo* bar**

<p><strong><em>foo</em> bar</strong></p>

Example 293

___foo_ bar__

<p><strong><em>foo</em> bar</strong></p>

Example 294

*foo **bar***

<p><em>foo <strong>bar</strong></em></p>

Example 295

_foo __bar___

<p><em>foo <strong>bar</strong></em></p>

Example 296

**foo *bar***

<p><strong>foo <em>bar</em></strong></p>

Example 297

__foo _bar___

<p><strong>foo <em>bar</em></strong></p>

Example 298

*foo **bar***

<p><em>foo <strong>bar</strong></em></p>

Example 299

_foo __bar___

<p><em>foo <strong>bar</strong></em></p>

Example 300

*foo *bar* baz*

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

Example 301

_foo _bar_ baz_

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

Example 302

**foo **bar** baz**

<p><strong>foo <strong>bar</strong> baz</strong></p>

Example 303

__foo __bar__ baz__

<p><strong>foo <strong>bar</strong> baz</strong></p>

Example 304

*foo **bar** baz*

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

Example 305

_foo __bar__ baz_

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

Example 306

**foo *bar* baz**

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

Example 307

__foo _bar_ baz__

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

Note that you cannot nest emphasis directly inside emphasis using the same delimiter, or strong emphasis directly inside strong emphasis:

Example 308

**foo**

<p><strong>foo</strong></p>

Example 309

****foo****

<p>****foo****</p>

For these nestings, you need to switch delimiters:

Example 310

*_foo_*

<p><em><em>foo</em></em></p>

Example 311

**__foo__**

<p><strong><strong>foo</strong></strong></p>

Note that a * followed by a * can close emphasis, and a ** followed by a * can close strong emphasis (and similarly for _ and __):

Example 312

*foo**

<p><em>foo</em>*</p>

Example 313

*foo *bar**

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

Example 314

**foo***

<p><strong>foo</strong>*</p>

Example 315

***foo* bar***

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

Example 316

***foo** bar***

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

The following contains no strong emphasis, because the opening delimiter is closed by the first * before bar:

Example 317

*foo**bar***

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

However, a string of four or more **** can never close emphasis:

Example 318

*foo****

<p>*foo****</p>

Note that there are some asymmetries here:

Example 319

*foo**

**foo*

<p><em>foo</em>*</p>
<p>**foo*</p>

Example 320

*foo *bar**

**foo* bar*

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

More cases with mismatched delimiters:

Example 321

**foo* bar*

<p>**foo* bar*</p>

Example 322

*bar***

<p><em>bar</em>**</p>

Example 323

***foo*

<p>***foo*</p>

Example 324

**bar***

<p><strong>bar</strong>*</p>

Example 325

***foo**

<p>***foo**</p>

Example 326

***foo *bar*

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

6.5 Links

A link contains a link label (the visible text), a 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 label. In reference links the destination and title are defined elsewhere in the document.

A link label consists of

an opening [, followed by
zero or more backtick code spans, autolinks, HTML tags, link labels, backslash-escaped ASCII punctuation characters, or non-] characters, followed by
a closing ].

These rules are motivated by the following intuitive ideas:

A link label is a container for inline elements.
The square brackets bind more tightly than emphasis markers, but less tightly than <> or `.
Link labels may contain material in matching square brackets.

A link destination consists of either

a sequence of zero or more characters between an opening < and a closing > that contains no line breaks or unescaped < or > characters, or
a nonempty sequence of characters that does not include ASCII space or control characters, and includes parentheses only if (a) they are backslash-escaped or (b) they are part of a balanced pair of unescaped parentheses that is not itself inside a balanced pair of unescaped parentheses.

A link title consists of either

a sequence of zero or more characters between straight double-quote characters ("), including a " character only if it is backslash-escaped, or
a sequence of zero or more characters between straight single-quote characters ('), including a ' character only if it is backslash-escaped, or
a sequence of zero or more characters between matching parentheses ((...)), including a ) character only if it is backslash-escaped.

An inline link consists of a link label 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 label (excluding the enclosing square brackets) parsed as inlines. 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 327

[link](/uri "title")

<p><a href="/uri" title="title">link</a></p>

The title may be omitted:

Example 328

[link](/uri)

<p><a href="/uri">link</a></p>

Both the title and the destination may be omitted:

Example 329

[link]()

<p><a href="">link</a></p>

Example 330

[link](<>)

<p><a href="">link</a></p>

If the destination contains spaces, it must be enclosed in pointy braces:

Example 331

[link](/my uri)

<p>[link](/my uri)</p>

Example 332

[link](</my uri>)

<p><a href="/my uri">link</a></p>

The destination cannot contain line breaks, even with pointy braces:

Example 333

[link](foo
bar)

<p>[link](foo
bar)</p>

One level of balanced parentheses is allowed without escaping:

Example 334

[link]((foo)and(bar))

<p><a href="(foo)and(bar)">link</a></p>

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

Example 335

[link](foo(and(bar)))

<p>[link](foo(and(bar)))</p>

Example 336

[link](foo(and\(bar\)))

<p><a href="foo(and(bar))">link</a></p>

Example 337

[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 338

[link](foo\)\:)

<p><a href="foo):">link</a></p>

URL-escaping and entities should be left alone inside the destination:

Example 339

[link](foo%20b&auml;)

<p><a href="foo%20b&auml;">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 340

[link]("title")

<p><a href="&quot;title&quot;">link</a></p>

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

Example 341

[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 entities may be used in titles:

Example 342

[link](/url "title \"&quot;")

<p><a href="/url" title="title &quot;&quot;">link</a></p>

Nested balanced quotes are not allowed without escaping:

Example 343

[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 344

[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, entities, 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 345

[link](   /uri
  "title"  )

<p><a href="/uri" title="title">link</a></p>

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

Example 346

[link] (/uri)

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

Note that this is not a link, because the closing ] occurs in an HTML tag:

Example 347

[foo <bar attr="](baz)">

<p>[foo <bar attr="](baz)"></p>

There are three kinds of reference links:

A full reference link consists of a link label, optional whitespace, and another link label that matches a link reference definition elsewhere in the document.

One label matches another just in case their normalized forms are equal. To normalize a label, perform the unicode case fold 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 348

[foo][bar]

[bar]: /url "title"

<p><a href="/url" title="title">foo</a></p>

The first label can contain inline content:

Example 349

[*foo\!*][bar]

[bar]: /url "title"

<p><a href="/url" title="title"><em>foo!</em></a></p>

Matching is case-insensitive:

Example 350

[foo][BaR]

[bar]: /url "title"

<p><a href="/url" title="title">foo</a></p>

Unicode case fold is used:

Example 351

[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 352

[Foo
  bar]: /url

[Baz][Foo bar]

<p><a href="/url">Baz</a></p>

There can be whitespace between the two labels:

Example 353

[foo] [bar]

[bar]: /url "title"

<p><a href="/url" title="title">foo</a></p>

Example 354

[foo]
[bar]

[bar]: /url "title"

<p><a href="/url" title="title">foo</a></p>

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

Example 355

[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 356

[bar][foo\!]

[foo!]: /url

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

A collapsed reference link consists of a link label that matches a link reference definition elsewhere in the document, optional whitespace, and 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 357

[foo][]

[foo]: /url "title"

<p><a href="/url" title="title">foo</a></p>

Example 358

[*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 359

[Foo][]

[foo]: /url "title"

<p><a href="/url" title="title">Foo</a></p>

As with full reference links, whitespace is allowed between the two sets of brackets:

Example 360

[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 361

[foo]

[foo]: /url "title"

<p><a href="/url" title="title">foo</a></p>

Example 362

[*foo* bar]

[*foo* bar]: /url "title"

<p><a href="/url" title="title"><em>foo</em> bar</a></p>

Example 363

[[*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 364

[Foo]

[foo]: /url "title"

<p><a href="/url" title="title">Foo</a></p>

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

Example 365

\[foo]

[foo]: /url "title"

<p>[foo]</p>

Note that this is a link, because link labels bind more tightly than emphasis:

Example 366

[foo*]: /url

*[foo*]

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

However, this is not, because link labels bind less tightly than code backticks:

Example 367

[foo`]: /url

[foo`]`

<p>[foo<code>]</code></p>

Link labels can contain matched square brackets:

Example 368

[[[foo]]]

[[[foo]]]: /url

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

Example 369

[[[foo]]]

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

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

For non-matching brackets, use backslash escapes:

Example 370

[\[foo]

[\[foo]: /url

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

Full references take precedence over shortcut references:

Example 371

[foo][bar]

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

<p><a href="/url2">foo</a></p>

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

Example 372

[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 373

[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 374

[foo][bar][baz]

[baz]: /url1
[foo]: /url2

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

6.6 Images

An (unescaped) exclamation mark (!) followed by a reference or inline link will be parsed as an image. The link label will be used as the image’s alt text, and the link title, if any, will be used as the image’s title.

Example 375

![foo](/url "title")

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

Example 376

![foo *bar*]

[foo *bar*]: train.jpg "train & tracks"

<p><img src="train.jpg" alt="foo &lt;em&gt;bar&lt;/em&gt;" title="train &amp; tracks" /></p>

Example 377

![foo *bar*][]

[foo *bar*]: train.jpg "train & tracks"

<p><img src="train.jpg" alt="foo &lt;em&gt;bar&lt;/em&gt;" title="train &amp; tracks" /></p>

Example 378

![foo *bar*][foobar]

[FOOBAR]: train.jpg "train & tracks"

<p><img src="train.jpg" alt="foo &lt;em&gt;bar&lt;/em&gt;" title="train &amp; tracks" /></p>

Example 379

![foo](train.jpg)

<p><img src="train.jpg" alt="foo" /></p>

Example 380

My ![foo bar](/path/to/train.jpg  "title"   )

<p>My <img src="/path/to/train.jpg" alt="foo bar" title="title" /></p>

Example 381

![foo](<url>)

<p><img src="url" alt="foo" /></p>

Example 382

![](/url)

<p><img src="/url" alt="" /></p>

Reference-style:

Example 383

![foo] [bar]

[bar]: /url

<p><img src="/url" alt="foo" /></p>

Example 384

![foo] [bar]

[BAR]: /url

<p><img src="/url" alt="foo" /></p>

Collapsed:

Example 385

![foo][]

[foo]: /url "title"

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

Example 386

![*foo* bar][]

[*foo* bar]: /url "title"

<p><img src="/url" alt="&lt;em&gt;foo&lt;/em&gt; bar" title="title" /></p>

The labels are case-insensitive:

Example 387

![Foo][]

[foo]: /url "title"

<p><img src="/url" alt="Foo" title="title" /></p>

As with full reference links, whitespace is allowed between the two sets of brackets:

Example 388

![foo] 
[]

[foo]: /url "title"

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

Shortcut:

Example 389

![foo]

[foo]: /url "title"

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

Example 390

![*foo* bar]

[*foo* bar]: /url "title"

<p><img src="/url" alt="&lt;em&gt;foo&lt;/em&gt; bar" title="title" /></p>

Example 391

![[foo]]

[[foo]]: /url "title"

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

The link labels are case-insensitive:

Example 392

![Foo]

[foo]: /url "title"

<p><img src="/url" alt="Foo" title="title" /></p>

If you just want bracketed text, you can backslash-escape the opening ! and [:

Example 393

\!\[foo]

[foo]: /url "title"

<p>![foo]</p>

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

Example 394

\![foo]

[foo]: /url "title"

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

6.7 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 not containing <, 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, you must use percent-encoding (e.g. %20 for a space).

The following schemes are recognized (case-insensitive): coap, doi, javascript, aaa, aaas, about, acap, cap, cid, crid, data, dav, dict, dns, file, ftp, geo, go, gopher, h323, http, https, iax, icap, im, imap, info, ipp, iris, iris.beep, iris.xpc, iris.xpcs, iris.lwz, ldap, mailto, mid, msrp, msrps, mtqp, mupdate, news, nfs, ni, nih, nntp, opaquelocktoken, pop, pres, rtsp, service, session, shttp, sieve, sip, sips, sms, snmp,soap.beep, soap.beeps, tag, tel, telnet, tftp, thismessage, tn3270, tip, tv, urn, vemmi, ws, wss, xcon, xcon-userid, xmlrpc.beep, xmlrpc.beeps, xmpp, z39.50r, z39.50s, adiumxtra, afp, afs, aim, apt,attachment, aw, beshare, bitcoin, bolo, callto, chrome,chrome-extension, com-eventbrite-attendee, content, cvs,dlna-playsingle, dlna-playcontainer, dtn, dvb, ed2k, facetime, feed, finger, fish, gg, git, gizmoproject, gtalk, hcp, icon, ipn, irc, irc6, ircs, itms, jar, jms, keyparc, lastfm, ldaps, magnet, maps, market,message, mms, ms-help, msnim, mumble, mvn, notes, oid, palm, paparazzi, platform, proxy, psyc, query, res, resource, rmi, rsync, rtmp, secondlife, sftp, sgn, skype, smb, soldat, spotify, ssh, steam, svn, teamspeak, things, udp, unreal, ut2004, ventrilo, view-source, webcal, wtai, wyciwyg, xfire, xri, ymsgr.

Here are some valid autolinks:

Example 395

<http://foo.bar.baz>

<p><a href="http://foo.bar.baz">http://foo.bar.baz</a></p>

Example 396

<http://foo.bar.baz?q=hello&id=22&boolean>

<p><a href="http://foo.bar.baz?q=hello&amp;id=22&amp;boolean">http://foo.bar.baz?q=hello&amp;id=22&amp;boolean</a></p>

Example 397

<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 398

<MAILTO:FOO@BAR.BAZ>

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

Spaces are not allowed in autolinks:

Example 399

<http://foo.bar/baz bim>

<p>&lt;http://foo.bar/baz bim&gt;</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 400

<foo@bar.baz.com>

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

Example 401

<foo+special@Bar.baz-bar0.com>

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

These are not autolinks:

Example 402

<>

<p>&lt;&gt;</p>

Example 403

<heck://bing.bong>

<p>&lt;heck://bing.bong&gt;</p>

Example 404

< http://foo.bar >

<p>&lt; http://foo.bar &gt;</p>

Example 405

<foo.bar.baz>

<p>&lt;foo.bar.baz&gt;</p>

Example 406

<localhost:5001/foo>

<p>&lt;localhost:5001/foo&gt;</p>

Example 407

http://google.com

<p>http://google.com</p>

Example 408

foo@bar.baz.com

<p>foo@bar.baz.com</p>

6.8 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 or digits.

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 spaces, ", ', =, <, >, 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 the string .

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, an element type declaration, or a CDATA section.

Here are some simple open tags:

Example 409

<a><bab><c2c>

<p><a><bab><c2c></p>

Empty elements:

Example 410

<a/><b2/>

<p><a/><b2/></p>

Whitespace is allowed:

Example 411

<a  /><b2
data="foo" >

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

With attributes:

Example 412

<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>

Illegal tag names, not parsed as HTML:

Example 413

<33> <__>

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

Illegal attribute names:

Example 414

<a h*#ref="hi">

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

Illegal attribute values:

Example 415

<a href="hi'> <a href=hi'>

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

Illegal whitespace:

Example 416

< a><
foo><bar/ >

<p>&lt; a&gt;&lt;
foo&gt;&lt;bar/ &gt;</p>

Missing whitespace:

Example 417

<a href='bar'title=title>

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

Closing tags:

Example 418

</a>
</foo >

<p></a>
</foo ></p>

Illegal attributes in closing tag:

Example 419

</a href="foo">

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

Comments:

Example 420

foo <!-- this is a
comment - with hyphen -->

<p>foo <!-- this is a
comment - with hyphen --></p>

Example 421

foo <!-- not a comment -- two hyphens -->

<p>foo &lt;!-- not a comment -- two hyphens --&gt;</p>

Processing instructions:

Example 422

foo <?php echo $a; ?>

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

Declarations:

Example 423

foo <!ELEMENT br EMPTY>

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

CDATA sections:

Example 424

foo <![CDATA[>&<]]>

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

Entities are preserved in HTML attributes:

Example 425

<a href="&ouml;">

<p><a href="&ouml;"></p>

Backslash escapes do not work in HTML attributes:

Example 426

<a href="\*">

<p><a href="\*"></p>

Example 427

<a href="\"">

<p>&lt;a href=&quot;&quot;&quot;&gt;</p>

6.9 Hard line breaks

A line break (not in a code span or HTML tag) that is preceded by two or more spaces is parsed as a linebreak (rendered in HTML as a <br /> tag):

Example 428

foo  
baz

<p>foo<br />
baz</p>

For a more visible alternative, a backslash before the newline may be used instead of two spaces:

Example 429

foo\
baz

<p>foo<br />
baz</p>

More than two spaces can be used:

Example 430

foo       
baz

<p>foo<br />
baz</p>

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

Example 431

foo  
     bar

<p>foo<br />
bar</p>

Example 432

foo\
     bar

<p>foo<br />
bar</p>

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

Example 433

*foo  
bar*

<p><em>foo<br />
bar</em></p>

Example 434

*foo\
bar*

<p><em>foo<br />
bar</em></p>

Line breaks do not occur inside code spans

Example 435

`code  
span`

<p><code>code span</code></p>

Example 436

`code\
span`

<p><code>code\ span</code></p>

or HTML tags:

Example 437

<a href="foo  
bar">

<p><a href="foo  
bar"></p>

Example 438

<a href="foo\
bar">

<p><a href="foo\
bar"></p>

6.10 Soft line breaks

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

Example 439

foo
baz

<p>foo
baz</p>

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

Example 440

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.

6.11 Strings

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

Example 441

hello $.;'there

<p>hello $.;'there</p>

Example 442

Foo χρῆν

<p>Foo χρῆν</p>

Internal spaces are preserved verbatim:

Example 443

Multiple     spaces

<p>Multiple     spaces</p>

7 Extensions

This section contains extensions to the Core Markdown syntax described above. They don’t need to be implemented to conform to this spec. However, if an implementation includes an extension with the same purpose as one of the extensions described here, this spec strongly recommends to implement the syntax described here.

7.1 Attributes

Certain elements may carry an attribute block. The following subsections list all elements that may contain attributes, see those for examples.

For inlines, the attribute block must immediately follow the element without any characters between the end of the inline and the start of the attribute block.
For horizontal rules, headers, fenced code blocks and reference links, there must be one or more space characters preceding the attribute block and any trailing whitespace is non-significant.
For paragraphs, block quotes and tight lists, the attribute block must start on a line that immediately follows the corresponding block. (Attributes on list items are not supported.)
For loose lists, the attribute block must start on a line that either immediately follows the list or is separated from it by only one blank line.

For the last two points in the above list the following must hold: the line(s) on which the attribute block resides must not contain any other characters except for leading spaces (i.e. indentation), which may be significant in determining to which element the attribute block belongs, but the start of the attribute block must be indented by exactly the same amount as the corresonding block itself. Trailing whitespace is non-significant.

An attribute block consists of a sequence of zero or more characters, between an unescaped opening LEFT CURLY BRACKET ({) and an unescaped closing RIGHT CURLY BRACKET (}), that includes curly brackets only if they are part of a balanced pair of unescaped double-quote or single-quote characters, and that does not contain a blank line. The characters between the opening and closing brackets form zero or more attributes which are separated by one or more whitespace characters (and may contain non-significant leading and trailing whitespace). The order of the attributes is not significant. An attribute consists of (a) a key-value pair, (b) an id-identifier or (c) a class-identifier.

1. A key-value pair consists of a key, immediately followed by an EQUALS SIGN (=) which is immediately followed by the value. The key follows the syntax of raw HTML attribute names. The value consists of either
- a sequence of zero or more characters that does not include ASCII space or control characters, or
- a sequence of zero or more characters between straight double-quote characters ("), including a " character only if it is backslash-escaped, or
- a sequence of zero or more characters between straight single-quote characters ('), including a ' character only if it is backslash-escaped.
1. An id-identifier consists of a NUMBER SIGN — also known as a hash — (#) immediately followed by one or more characters that does neither include ASCII space or control characters nor curly brackets. {#myId} is syntactic sugar for {id=myId}.
1. A class-identifier consists of a FULL STOP (.) immediately followed by one or more characters that does neither include ASCII space or control characters nor curly brackets. {.myClass} is syntactic sugar for {class=myClass}.

Markdown authors shouldn’t write multiple key-value pairs with the same key in an attribute block. However, to ease the burden of implementation, the behaviour in such cases is left undefined—although most implementations will probably parse the attributes sequentially and insert them into a map, which would result in a last-one-wins semantic.

If there are curly brackets that contain characters which don’t follow the rules outlined above and below, the curly brackets and the containing characters are not considered an attribute block but regular text and are to be interpreted accordingly.

7.1.1 Horizontal rules

Example 444

--- {#myId .myClass key=val key2="val 2"}

<hr id="myId" class="myClass" key="val" key2="val 2" />

There must be one or more space characters in front of the attribute block:

Example 445

---{.myClass}

<p>---{.myClass}</p>

Example 446

---     {#myId .myClass key=val key2="val 2"}

<hr id="myId" class="myClass" key="val" key2="val 2" />

Any whitespace (not only spaces) separate the attributes:

Example 447

--- {#myId     .myClass
key=val}

<hr id="myId" class="myClass" key="val" />

However, no blank lines are allowed within an attribute block:

Example 448

--- {#myId

.myClass}

<p>--- {#myId</p>
<p>.myClass}</p>

Any characters (except unescaped quotes of the same kind) are allowed in quoted attributes:

Example 449

---     {key="Hello \"World\"!" key2='Hello "World"!' key3="even new
lines and special chars like '=' or '`' are allowed"}

<hr key="Hello &quot;World&quot;!" key2="Hello &quot;World&quot;!" key3="even new lines and special chars like '=' or '`' are allowed"/>

7.1.2 ATX headers

Example 450

### foo {#myId .myClass key=val key2="val 2"}

<h3 id="myId" class="myClass" key="val" key2="val 2">foo</h3>

Or with a closing header sequence:

Example 451

### foo ### {#myId}

<h3 id="myId">foo</h3>

7.1.3 Setext headers

Example 452

Foo {#myId}
===========

<h1 id="myId">Foo</h1>

7.1.4 Fenced code blocks

Example 453

``` {.language-ruby #code1}
x = 1
```

<pre><code class="language-ruby">x = 1
</code></pre>

Info strings are syntactic sugar for classes, i.e. the following two fenced code blocks are identical:

```ruby
x = 1
```

``` {.language-ruby}
x = 1
```

As the attribute block must be preceded by a space, this may be surprising:

Example 454

```{.foo}
x = 1
```

<pre><code class="language-{.foo}">x = 1
</code></pre>

7.1.5 Reference Links

There must be one or more space characters preceding the attribute block in a reference link as well:

Example 455

[foo][bar]

[bar]: /url "title" {.myClass}

<p><a href="/url" title="title" class="myClass">foo</a></p>

Example 456

[foo][bar]

[bar]: /url "title"{.no-attribute}

<p>[foo][bar]</p>
<p>[bar]: /url "title"{.no-attribute}</p>

Example 457

[foo][bar]

[bar]: /url{.no-attribute}

<p><a href="/url%7B.no-attribute%7D">foo</a></p>

7.1.6 Paragraphs

Attribute blocks must start on a line following the paragraph.

Example 458

Paragraph with attributes.
{.myPar}

<p class="myPar">Paragraph with attributes.</p>

Example 459

Paragraph with attributes.
{.myPar
#myId}

<p class="myPar" id="myId">Paragraph with attributes.</p>

Example 460

Paragraph {.nope}

<p>Paragraph {.nope}</p>

Example 461

Paragraph

{.nope}

<p>Paragraph</p>
<p>{.nope}</p>

Attribute blocks for paragraphs must be indented exactly as much as the first line of the paragraph itself:

Example 462

Paragraph
 {.nope}

<p>Paragraph {.nope}</p>

7.1.7 Block quotes

Example 463

> Blockquote with attributes.
{.myBlockquote}

<blockquote class="myBlockquote">
<p>Blockquote with attributes.</p>
</blockquote>

Example 464

> Paragraph with attributes
> inside a block quote.
> {.myPar}

<blockquote>
<p class="myPar">Paragraph with attributes inside a block quote.</p>
</blockquote>

Attribute blocks for block quotes must be indented exactly as much as the > which is part of the block quote marker:

Example 465

   > Blockquote with attributes.
   {.myBlockquote}

<blockquote class="myBlockquote">
<p>Blockquote with attributes.</p>
</blockquote>

Example 466

> Blockquote without attributes.
  {.nope}

<blockquote>
<p>Blockquote without attributes. {.nope}</p>
</blockquote>

Example 467

> Blockquote with
lazy continuation
{.myBlockquote}

<blockquote class="myBlockquote">
<p>Blockquote with lazy continuation.</p>
</blockquote>

Example 468

> Blockquote with
lazy continuation
  {.nope}

<blockquote>
<p>Blockquote with lazy continuation {.nope}</p>
</blockquote>

7.1.8 Lists

Example 469

- list with
- attributes
{.myList}

<ul class="myList">
  <li>list with</li>
  <li>attributes</li>
</ul>

Example 470

- tight list without
- attributes

{.nope}

<ul>
  <li>tight list without</li>
  <li>attributes</li>
</ul>
<p>{.nope}</p>

Attribute blocks for lists must be indented exactly as much as the list markers:

Example 471

- a tight list
- without attributes
 {.nope}

<ul>
  <li>a tight list</li>
  <li>without attributes {.nope}</li>
</ul>

Example 472

- a tight list
- without attributes
  {.nope}

<ul>
  <li>a tight list</li>
  <li>without attributes {.nope}</li>
</ul>

Example 473

- one 1
- two 2
    - 2.1
    {.myList}

<ul>
  <li>one 1</li>
  <li>two 2
    <ul class="myList">
      <li>2.1</li>
    </ul>
  </li>
</ul>

Example 474

- a loose list

- with attributes

{.myList}

<ul class="myList">
  <li><p>a loose list</p></li>
  <li><p>with attributes</p></li>
</ul>

Example 475

- loose list

- with attributes
{.myList}

<ul class="myList">
  <li><p>loose list</p></li>
  <li><p>with attributes</p></li>
</ul>

Example 476

- a loose list

- without attributes


{.nope}

<ul>
  <li><p>a loose list</p></li>
  <li><p>without attributes</p></li>
</ul>
<p>{.nope}</p>

Example 477

- a loose list where

- the last paragraph has attributes.
  Note that the indentation of the
  attribute block is significant.
  {.myPar}

<ul>
  <li><p>a loose list where</p></li>
  <li><p class="myPar">the last paragraph has attributes</p></li>
</ul>

Attribute blocks themselves do not obey the lazy continuation rules. They can be used with lazy continuation paragraphs, however it is not recommended since it gets quickly confusing.

Example 478

- a loose list

- with lazy
continuation
{.myList}

<ul class="myList">
  <li><p>a loose list</p></li>
  <li><p>with lazy continuation</p></li>
</ul>

Example 479

- a tight list
{.nope}
- with lazy
continuation
  {.nope}

<ul>
  <li>a tight list {.nope}</li>
  <li>with lazy continuation {.nope}</li>
</ul>

Example 480

- a loose list

- with lazy
continuation
  {.myPar}

<ul>
  <li><p>a loose list</p></li>
  <li><p class="myPar">with lazy continuation</p></li>
</ul>

A list of blockquotes:

Example 481

- > a list where each
  > item is a blockquote
  > {.myPar}

- > to see what is possible
  > {.myPar}
  {.myBlockquote}
{.myList}

<ul class="myList">
  <li>
    <blockquote>
    <p class="myPar">a list where each item is a blockquote</p>
    </blockquote>
  </li>
  <li>
    <blockquote class="myBlockquote">
    <p class="myPar">to see what is possible</p>
    </blockquote>
  </li>
</ul>

Note that list items themselves cannot have attributes.

7.1.9 Code span

An attribute block follows the closing code span backtick immediately:

Example 482

`foo`{.myClass}

<p><code class="myClass">foo</code></p>

Example 483

`foo` {.no-attribute}

<p><code>foo</code> {.no-attribute}</p>

7.1.10 Emphasis and strong emphasis

An attribute block follows any closing emphasis character immediately:

Example 484

_foo_{.myClass}

<p><em class="myClass">foo</em></p>

Example 485

**foo**{.myClass}

<p><strong class="myClass">foo</strong></p>

7.1.11 Inline Links

An attribute block follows a link’s right parenthesis ()) immediately:

Example 486

[link](/uri){.myClass}

<p><a href="/uri" class="myClass">link</a></p>

7.1.12 Images

As images are defined as links preceded by an exclamation mark (!), the behaviour is already well-defined.

Example 487

![foo](/url){.myClass}

<p><img src="/url" alt="foo" class="myClass" /></p>

7.1.13 Spans

A span consists of

an opening [, followed by
zero or more characters parsed as inline (where neither the first nor the last character is an ASCII space or control character), followed by
a closing ], immediately followed by
a mandatory attribute block.

Example 488

[foo _bar_]{#myId}

<p><span id="myId">foo <em>bar</em></span></p>

Spaces before or after the span are not required:

Example 489

this[foo]{#myId}works

<p>this<span id="myId">foo</span>works</p>

But the span content mustn’t start or end with whitespace:

Example 490

[ does not]{} work

<p>[ does not]{} work</p>

Example 491

[does not ]{} work

<p>[does not ]{} work</p>

Empty attribute blocks are generally allowed:

Example 492

[foo]{}

<p><span>foo</span></p>

As are empty spans:

Example 493

[]{.glyphicon}

<p><span class="glyphicon"></span></p>

Note that reference links have their attributes in the reference part, thus this span is not to be confused with a reference link:

Example 494

a paragraph with [no reflink]{.myClass}

[no reflink]: http://test.com

<p>a paragraph with <span class="myClass">no reflink</span></p>

Appendix A: A parsing strategy

Overview

Parsing has two phases:

In the first phase, lines of input are consumed and the block structure of the document—its division into paragraphs, block quotes, list items, and so on—is constructed. Text is assigned to these blocks but not parsed. Link reference definitions are parsed and a map of links is constructed.
In the second phase, the raw text contents of paragraphs and headers are parsed into sequences of Markdown inline elements (strings, code spans, links, emphasis, and so on), using the map of link references constructed in phase 1.

The document tree

At each point in processing, the document is represented as a tree of blocks. The root of the tree is a document block. The document may have any number of other blocks as children. These children may, in turn, have other blocks as children. The last child of a block is normally considered open, meaning that subsequent lines of input can alter its contents. (Blocks that are not open are closed.) Here, for example, is a possible document tree, with the open blocks marked by arrows:

-> document
  -> block_quote
       paragraph
         "Lorem ipsum dolor\nsit amet."
    -> list (type=bullet tight=true bullet_char=-)
         list_item
           paragraph
             "Qui *quodsi iracundia*"
      -> list_item
        -> paragraph
             "aliquando id"

How source lines alter the document tree

Each line that is processed has an effect on this tree. The line is analyzed and, depending on its contents, the document may be altered in one or more of the following ways:

One or more open blocks may be closed.
One or more new blocks may be created as children of the last open block.
Text may be added to the last (deepest) open block remaining on the tree.

Once a line has been incorporated into the tree in this way, it can be discarded, so input can be read in a stream.

We can see how this works by considering how the tree above is generated by four lines of Markdown:

> Lorem ipsum dolor
sit amet.
> - Qui *quodsi iracundia*
> - aliquando id

At the outset, our document model is just

-> document

The first line of our text,

> Lorem ipsum dolor

causes a block_quote block to be created as a child of our open document block, and a paragraph block as a child of the block_quote. Then the text is added to the last open block, the paragraph:

-> document
  -> block_quote
    -> paragraph
         "Lorem ipsum dolor"

The next line,

sit amet.

is a “lazy continuation” of the open paragraph, so it gets added to the paragraph’s text:

-> document
  -> block_quote
    -> paragraph
         "Lorem ipsum dolor\nsit amet."

The third line,

> - Qui *quodsi iracundia*

causes the paragraph block to be closed, and a new list block opened as a child of the block_quote. A list_item is also added as a child of the list, and a paragraph as a child of the list_item. The text is then added to the new paragraph:

-> document
  -> block_quote
       paragraph
         "Lorem ipsum dolor\nsit amet."
    -> list (type=bullet tight=true bullet_char=-)
      -> list_item
        -> paragraph
             "Qui *quodsi iracundia*"

The fourth line,

> - aliquando id

causes the list_item (and its child the paragraph) to be closed, and a new list_item opened up as child of the list. A paragraph is added as a child of the new list_item, to contain the text. We thus obtain the final tree:

-> document
  -> block_quote
       paragraph
         "Lorem ipsum dolor\nsit amet."
    -> list (type=bullet tight=true bullet_char=-)
         list_item
           paragraph
             "Qui *quodsi iracundia*"
      -> list_item
        -> paragraph
             "aliquando id"

From block structure to the final document

Once all of the input has been parsed, all open blocks are closed.

We then “walk the tree,” visiting every node, and parse raw string contents of paragraphs and headers as inlines. At this point we have seen all the link reference definitions, so we can resolve reference links as we go.

document
  block_quote
    paragraph
      str "Lorem ipsum dolor"
      softbreak
      str "sit amet."
    list (type=bullet tight=true bullet_char=-)
      list_item
        paragraph
          str "Qui "
          emph
            str "quodsi iracundia"
      list_item
        paragraph
          str "aliquando id"

Notice how the newline in the first paragraph has been parsed as a softbreak, and the asterisks in the first list item have become an emph.

The document can be rendered as HTML, or in any other format, given an appropriate renderer.