# CommonMark Spec

Version 0.31.2 (2024-01-28)
John MacFarlane
CommonMark Spec by John MacFarlane is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

# 1Introduction

## 1.1What is Markdown?

Markdown is a plain text format for writing structured documents, based on conventions for indicating formatting in email and usenet posts. It was developed by John Gruber (with help from Aaron Swartz) and released in 2004 in the form of a syntax description and a Perl script (`Markdown.pl`) for converting Markdown to HTML. In the next decade, dozens of implementations were developed in many languages. Some extended the original Markdown syntax with conventions for footnotes, tables, and other document elements. Some allowed Markdown documents to be rendered in formats other than HTML. Websites like Reddit, StackOverflow, and GitHub had millions of people using Markdown. And Markdown started to be used beyond the web, to author books, articles, slide shows, letters, and lecture notes.

What distinguishes Markdown from many other lightweight markup syntaxes, which are often easier to write, is its readability. As Gruber writes:

> The overriding design goal for Markdown’s formatting syntax is to make it as readable as possible. The idea is that a Markdown-formatted document should be publishable as-is, as plain text, without looking like it’s been marked up with tags or formatting instructions. (https://daringfireball.net/projects/markdown/)

The point can be illustrated by comparing a sample of AsciiDoc with an equivalent sample of Markdown. Here is a sample of AsciiDoc from the AsciiDoc manual:

    1. List item one.
    +
    List item one continued with a second paragraph followed by an
    Indented block.
    +
    .................
    $ ls *.sh
    $ mv *.sh ~/tmp
    .................
    +
    List item continued with a third paragraph.

    2. List item two continued with an open block.
    +
    --
    This paragraph is part of the preceding list item.

    a. This list is nested and does not require explicit item
    continuation.
    +
    This paragraph is part of the preceding list item.

    b. List item b.

    This paragraph belongs to item two of the outer list.
    --

And here is the equivalent in Markdown:

    1.  List item one.

        List item one continued with a second paragraph followed by an
        Indented block.

            $ ls *.sh
            $ mv *.sh ~/tmp

        List item continued with a third paragraph.

    2.  List item two continued with an open block.

        This paragraph is part of the preceding list item.

        1. This list is nested and does not require explicit item continuation.

           This paragraph is part of the preceding list item.

        2. List item b.

        This paragraph belongs to item two of the outer list.

The AsciiDoc version is, arguably, easier to write. You don’t need to worry about indentation. But the Markdown version is much easier to read. The nesting of list items is apparent to the eye in the source, not just in the processed document.

## 1.2Why 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:

1. How much indentation is needed for a sublist? The spec says that continuation paragraphs need to be indented four spaces, but is not fully explicit about sublists. It is natural to think that they, too, must be indented four spaces, but `Markdown.pl` does not require that. This is hardly a “corner case,” and divergences between implementations on this issue often lead to surprises for users in real documents. (See this comment by John Gruber.)

2. Is a blank line needed before a block quote or heading? Most implementations do not require the blank line. However, this can lead to unexpected results in hard-wrapped text, and also to ambiguities in parsing (note that some implementations put the heading inside the blockquote, while others do not). (John Gruber has also spoken in favor of requiring the blank lines.)

3. Is a blank line needed before an indented code block? (`Markdown.pl` requires it, but this is not mentioned in the documentation, and some implementations do not require it.)

       paragraph
           code?

4. What is the exact rule for determining when list items get wrapped in `<p>` tags? Can a list be partially “loose” and partially “tight”? What should we do with a list like this?

       1. one

       2. two
       3. three

   Or this?

       1.  one
           - a

           - b
       2.  two

   (There are some relevant comments by John Gruber here.)

5. Can list markers be indented? Can ordered list markers be right-aligned?

        8. item 1
        9. item 2
       10. item 2a

6. Is this one list with a thematic break in its second item, or two lists separated by a thematic break?

       * a
       * * * * *
       * b

7. When list markers change from numbers to bullets, do we have two lists or one? (The Markdown syntax description suggests two, but the perl scripts and many other implementations produce one.)

       1. fee
       2. fie
       -  foe
       -  fum

8. What are the precedence rules for the markers of inline structure? For example, is the following a valid link, or does the code span take precedence ?

       [a backtick (`)](/url) and [another backtick (`)](/url).

9. What are the precedence rules for markers of emphasis and strong emphasis? For example, how should the following be parsed?

       *foo *bar* baz*

10. 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`

11. Can list items include section headings? (`Markdown.pl` does not allow this, but does allow blockquotes to include headings.)

        - # Heading

12. Can list items be empty?

        * a
        *
        * b

13. Can link references be defined inside block quotes or list items?

        > Blockquote [foo].
        >
        > [foo]: /url

14. 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.

## 1.3About this document

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

    python test/spec_tests.py --spec spec.txt --program PROGRAM

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

Note that not every feature of the HTML samples is mandated by the spec. For example, the spec says what counts as a link destination, but it doesn’t mandate that non-ASCII characters in the URL be percent-encoded. To use the automatic tests, implementers will need to provide a renderer that conforms to the expectations of the spec examples (percent-encoding non-ASCII characters in URLs). But a conforming implementation can use a different renderer and may choose not to percent-encode non-ASCII characters in URLs.

This document is generated from a text file, `spec.txt`, written in Markdown with a small extension for the side-by-side tests. The script `tools/makespec.py` can be used to convert `spec.txt` into HTML or CommonMark (which can then be converted into other formats).

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

# 2Preliminaries

## 2.1Characters and lines

Any sequence of characters is a valid CommonMark document.

A character is a Unicode code point. Although some code points (for example, combining accents) do not correspond to characters in an intuitive sense, all code points count as characters for purposes of this spec.

This spec does not specify an encoding; it thinks of lines as composed of characters rather than bytes. A conforming parser may be limited to a certain encoding.

A line is a sequence of zero or more characters other than line feed (`U+000A`) or carriage return (`U+000D`), followed by a line ending or by the end of file.

A line ending is a line feed (`U+000A`), a carriage return (`U+000D`) not followed by a line feed, or a carriage return and a following line feed.

A line containing no characters, or a line containing only spaces (`U+0020`) or tabs (`U+0009`), is called a blank line.

The following definitions of character classes will be used in this spec:

A Unicode whitespace character is a character in the Unicode `Zs` general category, or a tab (`U+0009`), line feed (`U+000A`), form feed (`U+000C`), or carriage return (`U+000D`).

Unicode whitespace is a sequence of one or more Unicode whitespace characters.

A tab is `U+0009`.

A space is `U+0020`.

An ASCII control character is a character between `U+0000–1F` (both including) or `U+007F`.

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

A Unicode punctuation character is a character in the Unicode `P` (puncuation) or `S` (symbol) general categories.

## 2.2Tabs

Tabs in lines are not expanded to spaces. However, in contexts where spaces help to define block structure, tabs behave as if they were replaced by spaces with a tab stop of 4 characters.

Thus, for example, a tab can be used instead of four spaces in an indented code block. (Note, however, that internal tabs are passed through as literal tabs, not expanded to spaces.)

Example 1Try It

    →foo→baz→→bim

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

Example 2Try It

      →foo→baz→→bim

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

Example 3Try It

        a→a
        ὐ→a

    <pre><code>a→a
    ὐ→a
    </code></pre>

In the following example, a continuation paragraph of a list item is indented with a tab; this has exactly the same effect as indentation with four spaces would:

Example 4Try It

      - foo

    →bar

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

Example 5Try It

    - foo

    →→bar

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

Normally the `>` that begins a block quote may be followed optionally by a space, which is not considered part of the content. In the following case `>` is followed by a tab, which is treated as if it were expanded into three spaces. Since one of these spaces is considered part of the delimiter, `foo` is considered to be indented six spaces inside the block quote context, so we get an indented code block starting with two spaces.

Example 6Try It

    >→→foo

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

Example 7Try It

    -→→foo

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

Example 8Try It

        foo
    →bar

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

Example 9Try It

     - foo
       - bar
    → - baz

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

Example 10Try It

    #→Foo

    <h1>Foo</h1>

Example 11Try It

    *→*→*→

    <hr />

## 2.3Insecure characters

For security reasons, the Unicode character `U+0000` must be replaced with the REPLACEMENT CHARACTER (`U+FFFD`).

## 2.4Backslash escapes

Any ASCII punctuation character may be backslash-escaped:

Example 12Try It

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

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

Backslashes before other characters are treated as literal backslashes:

Example 13Try It

    \→\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 14Try It

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

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

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

Example 15Try It

    \\*emphasis*

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

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

Example 16Try It

    foo\
    bar

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

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

Example 17Try It

    `` \[\` ``

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

Example 18Try It

        \[\]

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

Example 19Try It

    ~~~
    \[\]
    ~~~

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

Example 20Try It

    <https://example.com?find=\*>

    <p><a href="https://example.com?find=%5C*">https://example.com?find=\*</a></p>

Example 21Try It

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

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

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

Example 22Try It

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

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

Example 23Try It

    [foo]

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

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

Example 24Try It

    ``` foo\+bar
    foo
    ```

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

## 2.5Entity and numeric character references

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

- Entity and character references are not recognized in code blocks and code spans.

- Entity and character references cannot stand in place of special characters that define structural elements in CommonMark. For example, although `&#42;` can be used in place of a literal `*` character, `&#42;` cannot replace `*` in emphasis delimiters, bullet list markers, or thematic breaks.

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

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

Example 25Try It

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

    <p>  &amp; © Æ Ď
    ¾ ℋ ⅆ
    ∲ ≧̸</p>

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

Example 26Try It

    &#35; &#1234; &#992; &#0;

    <p># Ӓ Ϡ �</p>

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

Example 27Try It

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

    <p>&quot; ആ ಫ</p>

Here are some nonentities:

Example 28Try It

    &nbsp &x; &#; &#x;
    &#87654321;
    &#abcdef0;
    &ThisIsNotDefined; &hi?;

    <p>&amp;nbsp &amp;x; &amp;#; &amp;#x;
    &amp;#87654321;
    &amp;#abcdef0;
    &amp;ThisIsNotDefined; &amp;hi?;</p>

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

Example 29Try It

    &copy

    <p>&amp;copy</p>

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

Example 30Try It

    &MadeUpEntity;

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

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

Example 31Try It

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

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

Example 32Try It

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

    <p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p>

Example 33Try It

    [foo]

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

    <p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p>

Example 34Try It

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

    <pre><code class="language-föö">foo
    </code></pre>

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

Example 35Try It

    `f&ouml;&ouml;`

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

Example 36Try It

        f&ouml;f&ouml;

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

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

Example 37Try It

    &#42;foo&#42;
    *foo*

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

Example 38Try It

    &#42; foo

    * foo

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

Example 39Try It

    foo&#10;&#10;bar

    <p>foo

    bar</p>

Example 40Try It

    &#9;foo

    <p>→foo</p>

Example 41Try It

    [a](url &quot;tit&quot;)

    <p>[a](url &quot;tit&quot;)</p>

# 3Blocks and inlines

We can think of a document as a sequence of blocks—structural elements like paragraphs, block quotations, lists, headings, rules, and code blocks. Some blocks (like block quotes and list items) contain other blocks; others (like headings and paragraphs) contain inline content—text, links, emphasized text, images, code spans, and so on.

## 3.1Precedence

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 42Try It

    - `one
    - two`

    <ul>
    <li>`one</li>
    <li>two`</li>
    </ul>

This means that parsing can proceed in two steps: first, the block structure of the document can be discerned; second, text lines inside paragraphs, headings, and other block constructs can be parsed for inline structure. The second step requires information about link reference definitions that will be available only at the end of the first step. Note that the first step requires processing lines in sequence, but the second can be parallelized, since the inline parsing of one block element does not affect the inline parsing of any other.

## 3.2Container blocks and leaf blocks

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

# 4Leaf blocks

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

## 4.1Thematic breaks

A line consisting of optionally up to three spaces of indentation, followed by a sequence of three or more matching `-`, `_`, or `*` characters, each followed optionally by any number of spaces or tabs, forms a thematic break.

Example 43Try It

    ***
    ---
    ___

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

Wrong characters:

Example 44Try It

    +++

    <p>+++</p>

Example 45Try It

    ===

    <p>===</p>

Not enough characters:

Example 46Try It

    --
    **
    __

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

Up to three spaces of indentation are allowed:

Example 47Try It

     ***
      ***
       ***

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

Four spaces of indentation is too many:

Example 48Try It

        ***

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

Example 49Try It

    Foo
        ***

    <p>Foo
    ***</p>

More than three characters may be used:

Example 50Try It

    _____________________________________

    <hr />

Spaces and tabs are allowed between the characters:

Example 51Try It

     - - -

    <hr />

Example 52Try It

     **  * ** * ** * **

    <hr />

Example 53Try It

    -     -      -      -

    <hr />

Spaces and tabs are allowed at the end:

Example 54Try It

    - - - -

    <hr />

However, no other characters may occur in the line:

Example 55Try It

    _ _ _ _ a

    a------

    ---a---

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

It is required that all of the characters other than spaces or tabs be the same. So, this is not a thematic break:

Example 56Try It

     *-*

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

Thematic breaks do not need blank lines before or after:

Example 57Try It

    - foo
    ***
    - bar

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

Thematic breaks can interrupt a paragraph:

Example 58Try It

    Foo
    ***
    bar

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

If a line of dashes that meets the above conditions for being a thematic break could also be interpreted as the underline of a setext heading, the interpretation as a setext heading takes precedence. Thus, for example, this is a setext heading, not a paragraph followed by a thematic break:

Example 59Try It

    Foo
    ---
    bar

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

When both a thematic break and a list item are possible interpretations of a line, the thematic break takes precedence:

Example 60Try It

    * Foo
    * * *
    * Bar

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

If you want a thematic break in a list item, use a different bullet:

Example 61Try It

    - Foo
    - * * *

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

## 4.2ATX headings

An ATX heading consists of a string of characters, parsed as inline content, between an opening sequence of 1–6 unescaped `#` characters and an optional closing sequence of any number of unescaped `#` characters. The opening sequence of `#` characters must be followed by spaces or tabs, or by the end of line. The optional closing sequence of `#`s must be preceded by spaces or tabs and may be followed by spaces or tabs only. The opening `#` character may be preceded by up to three spaces of indentation. The raw contents of the heading are stripped of leading and trailing space or tabs before being parsed as inline content. The heading level is equal to the number of `#` characters in the opening sequence.

Simple headings:

Example 62Try It

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

    <h1>foo</h1>
    <h2>foo</h2>
    <h3>foo</h3>
    <h4>foo</h4>
    <h5>foo</h5>
    <h6>foo</h6>

More than six `#` characters is not a heading:

Example 63Try It

    ####### foo

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

At least one space or tab is required between the `#` characters and the heading’s contents, unless the heading is empty. Note that many implementations currently do not require the space. However, the space was required by the original ATX implementation, and it helps prevent things like the following from being parsed as headings:

Example 64Try It

    #5 bolt

    #hashtag

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

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

Example 65Try It

    \## foo

    <p>## foo</p>

Contents are parsed as inlines:

Example 66Try It

    # foo *bar* \*baz\*

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

Leading and trailing spaces or tabs are ignored in parsing inline content:

Example 67Try It

    #                  foo

    <h1>foo</h1>

Up to three spaces of indentation are allowed:

Example 68Try It

     ### foo
      ## foo
       # foo

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

Four spaces of indentation is too many:

Example 69Try It

        # foo

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

Example 70Try It

    foo
        # bar

    <p>foo
    # bar</p>

A closing sequence of `#` characters is optional:

Example 71Try It

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

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

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

Example 72Try It

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

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

Spaces or tabs are allowed after the closing sequence:

Example 73Try It

    ### foo ###

    <h3>foo</h3>

A sequence of `#` characters with anything but spaces or tabs following it is not a closing sequence, but counts as part of the contents of the heading:

Example 74Try It

    ### foo ### b

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

The closing sequence must be preceded by a space or tab:

Example 75Try It

    # foo#

    <h1>foo#</h1>

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

Example 76Try It

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

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

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

Example 77Try It

    ****
    ## foo
    ****

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

Example 78Try It

    Foo bar
    # baz
    Bar foo

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

ATX headings can be empty:

Example 79Try It

    ##
    #
    ### ###

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

## 4.3Setext headings

A setext heading consists of one or more lines of text, not interrupted by a blank line, of which the first line does not have more than 3 spaces of indentation, followed by a setext heading underline. The lines of text must be such that, were they not followed by the setext heading underline, they would be interpreted as a paragraph: they cannot be interpretable as a code fence, ATX heading, block quote, thematic break, list item, or HTML block.

A setext heading underline is a sequence of `=` characters or a sequence of `-` characters, with no more than 3 spaces of indentation and any number of trailing spaces or tabs.

The heading is a level 1 heading if `=` characters are used in the setext heading underline, and a level 2 heading if `-` characters are used. The contents of the heading are the result of parsing the preceding lines of text as CommonMark inline content.

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

Simple examples:

Example 80Try It

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

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

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

The content of the header may span more than one line:

Example 81Try It

    Foo *bar
    baz*
    ====

    <h1>Foo <em>bar
    baz</em></h1>

The contents are the result of parsing the headings’s raw content as inlines. The heading’s raw content is formed by concatenating the lines and removing initial and final spaces or tabs.

Example 82Try It

      Foo *bar
    baz*→
    ====

    <h1>Foo <em>bar
    baz</em></h1>

The underlining can be any length:

Example 83Try It

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

    Foo
    =

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

The heading content can be preceded by up to three spaces of indentation, and need not line up with the underlining:

Example 84Try It

       Foo
    ---

      Foo
    -----

      Foo
      ===

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

Four spaces of indentation is too many:

Example 85Try It

        Foo
        ---

        Foo
    ---

    <pre><code>Foo
    ---

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

The setext heading underline can be preceded by up to three spaces of indentation, and may have trailing spaces or tabs:

Example 86Try It

    Foo
       ----

    <h2>Foo</h2>

Four spaces of indentation is too many:

Example 87Try It

    Foo
        ---

    <p>Foo
    ---</p>

The setext heading underline cannot contain internal spaces or tabs:

Example 88Try It

    Foo
    = =

    Foo
    --- -

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

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

Example 89Try It

    Foo
    -----

    <h2>Foo</h2>

Nor does a backslash at the end:

Example 90Try It

    Foo\
    ----

    <h2>Foo\</h2>

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

Example 91Try It

    `Foo
    ----
    `

    <a title="a lot
    ---
    of dashes"/>

    <h2>`Foo</h2>
    <p>`</p>
    <h2>&lt;a title=&quot;a lot</h2>
    <p>of dashes&quot;/&gt;</p>

The setext heading underline cannot be a lazy continuation line in a list item or block quote:

Example 92Try It

    > Foo
    ---

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

Example 93Try It

    > foo
    bar
    ===

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

Example 94Try It

    - Foo
    ---

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

A blank line is needed between a paragraph and a following setext heading, since otherwise the paragraph becomes part of the heading’s content:

Example 95Try It

    Foo
    Bar
    ---

    <h2>Foo
    Bar</h2>

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

Example 96Try It

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

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

Setext headings cannot be empty:

Example 97Try It

    ====

    <p>====</p>

Setext heading text lines must not be interpretable as block constructs other than paragraphs. So, the line of dashes in these examples gets interpreted as a thematic break:

Example 98Try It

    ---
    ---

    <hr />
    <hr />

Example 99Try It

    - foo
    -----

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

Example 100Try It

        foo
    ---

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

Example 101Try It

    > foo
    -----

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

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

Example 102Try It

    \> foo
    ------

    <h2>&gt; foo</h2>

Compatibility note: Most existing Markdown implementations do not allow the text of setext headings to span multiple lines. But there is no consensus about how to interpret

    Foo
    bar
    ---
    baz

One can find four different interpretations:

1. paragraph “Foo”, heading “bar”, paragraph “baz”
2. paragraph “Foo bar”, thematic break, paragraph “baz”
3. paragraph “Foo bar — baz”
4. heading “Foo bar”, paragraph “baz”

We find interpretation 4 most natural, and interpretation 4 increases the expressive power of CommonMark, by allowing multiline headings. Authors who want interpretation 1 can put a blank line after the first paragraph:

Example 103Try It

    Foo

    bar
    ---
    baz

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

Authors who want interpretation 2 can put blank lines around the thematic break,

Example 104Try It

    Foo
    bar

    ---

    baz

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

or use a thematic break that cannot count as a setext heading underline, such as

Example 105Try It

    Foo
    bar
    * * *
    baz

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

Authors who want interpretation 3 can use backslash escapes:

Example 106Try It

    Foo
    bar
    \---
    baz

    <p>Foo
    bar
    ---
    baz</p>

## 4.4Indented 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 preceded by four or more spaces of indentation. The contents of the code block are the literal contents of the lines, including trailing line endings, minus four spaces of indentation. An indented code block has no info string.

An indented code block cannot interrupt a paragraph, so there must be a blank line between a paragraph and a following indented code block. (A blank line is not needed, however, between a code block and a following paragraph.)

Example 107Try It

        a simple
          indented code block

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

If there is any ambiguity between an interpretation of indentation as a code block and as indicating that material belongs to a list item, the list item interpretation takes precedence:

Example 108Try It

      - foo

        bar

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

Example 109Try It

    1.  foo

        - bar

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

The contents of a code block are literal text, and do not get parsed as Markdown:

Example 110Try It

        <a/>
        *hi*

        - one

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

    - one
    </code></pre>

Here we have three chunks separated by blank lines:

Example 111Try It

        chunk1

        chunk2

        chunk3

    <pre><code>chunk1

    chunk2

    chunk3
    </code></pre>

Any initial spaces or tabs beyond four spaces of indentation will be included in the content, even in interior blank lines:

Example 112Try It

        chunk1

          chunk2

    <pre><code>chunk1

      chunk2
    </code></pre>

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

Example 113Try It

    Foo
        bar

    <p>Foo
    bar</p>

However, any non-blank line with fewer than four spaces of indentation ends the code block immediately. So a paragraph may occur immediately after indented code:

Example 114Try It

        foo
    bar

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

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

Example 115Try It

    # Heading
        foo
    Heading
    ------
        foo
    ----

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

The first line can be preceded by more than four spaces of indentation:

Example 116Try It

            foo
        bar

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

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

Example 117Try It

        foo

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

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

Example 118Try It

        foo

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

## 4.5Fenced 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, preceded by up to three spaces of indentation.

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

The content of the code block consists of all subsequent lines, until a closing code fence of the same type as the code block began with (backticks or tildes), and with at least as many backticks or tildes as the opening code fence. If the leading code fence is preceded by N spaces of indentation, 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 N spaces or less, all of the indentation is removed.)

The closing code fence may be preceded by up to three spaces of indentation, and may be followed only by spaces or tabs, 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 downside 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 119Try It

    ```
    <
     >
    ```

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

With tildes:

Example 120Try It

    ~~~
    <
     >
    ~~~

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

Fewer than three backticks is not enough:

Example 121Try It

    ``
    foo
    ``

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

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

Example 122Try It

    ```
    aaa
    ~~~
    ```

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

Example 123Try It

    ~~~
    aaa
    ```
    ~~~

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

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

Example 124Try It

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

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

Example 125Try It

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

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

Unclosed code blocks are closed by the end of the document (or the enclosing block quote or list item):

Example 126Try It

    ```

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

Example 127Try It

    `````

    ```
    aaa

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

Example 128Try It

    > ```
    > aaa

    bbb

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

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

Example 129Try It

    ```

    ```

    <pre><code>

    </code></pre>

A code block can be empty:

Example 130Try It

    ```
    ```

    <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 131Try It

     ```
     aaa
    aaa
    ```

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

Example 132Try It

      ```
    aaa
      aaa
    aaa
      ```

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

Example 133Try It

       ```
       aaa
        aaa
      aaa
       ```

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

Four spaces of indentation is too many:

Example 134Try It

        ```
        aaa
        ```

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

Closing fences may be preceded by up to three spaces of indentation, and their indentation need not match that of the opening fence:

Example 135Try It

    ```
    aaa
      ```

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

Example 136Try It

       ```
    aaa
      ```

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

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

Example 137Try It

    ```
    aaa
        ```

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

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

Example 138Try It

    ``` ```
    aaa

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

Example 139Try It

    ~~~~~~
    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 140Try It

    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 141Try It

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

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

An info string can be provided after the opening code fence. Although this spec doesn’t mandate any particular treatment of the info string, the first word is typically used to specify the language of the code block. In HTML output, the language is normally indicated by adding a class to the `code` element consisting of `language-` followed by the language name.

Example 142Try It

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

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

Example 143Try It

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

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

Example 144Try It

    ````;
    ````

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

Info strings for backtick code blocks cannot contain backticks:

Example 145Try It

    ``` aa ```
    foo

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

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

Example 146Try It

    ~~~ aa ``` ~~~
    foo
    ~~~

    <pre><code class="language-aa">foo
    </code></pre>

Closing code fences cannot have info strings:

Example 147Try It

    ```
    ``` aaa
    ```

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

## 4.6HTML blocks

An HTML block is a group of lines that is treated as raw HTML (and will not be escaped in HTML output).

There are seven kinds of HTML block, which can be defined by their start and end conditions. The block begins with a line that meets a start condition (after up to three optional spaces of indentation). It ends with the first subsequent line that meets a matching end condition, or the last line of the document, or the last line of the container block containing the current HTML block, if no line is encountered that meets the end condition. If the first line meets both the start condition and the end condition, the block will contain just that line.

1. Start condition: line begins with the string `<pre`, `<script`, `<style`, or `<textarea` (case-insensitive), followed by a space, a tab, the string `>`, or the end of the line.
   End condition: line contains an end tag `</pre>`, `</script>`, `</style>`, or `</textarea>` (case-insensitive; it need not match the start tag).

2. Start condition: line begins with the string `<!--`.
   End condition: line contains the string `-->`.

3. Start condition: line begins with the string `<?`.
   End condition: line contains the string `?>`.

4. Start condition: line begins with the string `<!` followed by an ASCII letter.
   End condition: line contains the character `>`.

5. Start condition: line begins with the string `<![CDATA[`.
   End condition: line contains the string `]]>`.

6. Start condition: line begins with the string `<` or `</` followed by one of the strings (case-insensitive) `address`, `article`, `aside`, `base`, `basefont`, `blockquote`, `body`, `caption`, `center`, `col`, `colgroup`, `dd`, `details`, `dialog`, `dir`, `div`, `dl`, `dt`, `fieldset`, `figcaption`, `figure`, `footer`, `form`, `frame`, `frameset`, `h1`, `h2`, `h3`, `h4`, `h5`, `h6`, `head`, `header`, `hr`, `html`, `iframe`, `legend`, `li`, `link`, `main`, `menu`, `menuitem`, `nav`, `noframes`, `ol`, `optgroup`, `option`, `p`, `param`, `search`, `section`, `summary`, `table`, `tbody`, `td`, `tfoot`, `th`, `thead`, `title`, `tr`, `track`, `ul`, followed by a space, a tab, the end of the line, the string `>`, or the string `/>`.
   End condition: line is followed by a blank line.

7. Start condition: line begins with a complete open tag (with any tag name other than `pre`, `script`, `style`, or `textarea`) or a complete closing tag, followed by zero or more spaces and tabs, followed by the end of the line.
   End condition: line is followed by a blank line.

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

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

Example 148Try It

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

    _world_.
    </pre>
    </td></tr></table>

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

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

All types of HTML blocks except type 7 may interrupt a paragraph. Blocks of type 7 may not interrupt a paragraph. (This restriction is intended to prevent unwanted interpretation of long tags inside a wrapped paragraph as starting HTML blocks.)

Some simple examples follow. Here are some basic HTML blocks of type 6:

Example 149Try It

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

    okay.

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

Example 150Try It

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

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

A block can also start with a closing tag:

Example 151Try It

    </div>
    *foo*

    </div>
    *foo*

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

Example 152Try It

    <DIV CLASS="foo">

    *Markdown*

    </DIV>

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

The tag on the first line can be partial, as long as it is split where there would be whitespace:

Example 153Try It

    <div id="foo"
      class="bar">
    </div>

    <div id="foo"
      class="bar">
    </div>

Example 154Try It

    <div id="foo" class="bar
      baz">
    </div>

    <div id="foo" class="bar
      baz">
    </div>

An open tag need not be closed:

Example 155Try It

    <div>
    *foo*

    *bar*

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

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

Example 156Try It

    <div id="foo"
    *hi*

    <div id="foo"
    *hi*

Example 157Try It

    <div class
    foo

    <div class
    foo

The initial tag doesn’t even need to be a valid tag, as long as it starts like one:

Example 158Try It

    <div *???-&&&-<---
    *foo*

    <div *???-&&&-<---
    *foo*

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

Example 159Try It

    <div><a href="bar">*foo*</a></div>

    <div><a href="bar">*foo*</a></div>

Example 160Try It

    <table><tr><td>
    foo
    </td></tr></table>

    <table><tr><td>
    foo
    </td></tr></table>

Everything until the next blank line or end of document gets included in the HTML block. So, in the following example, what looks like a Markdown code block is actually part of the HTML block, which continues until a blank line or the end of the document is reached:

Example 161Try It

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

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

To start an HTML block with a tag that is not in the list of block-level tags in (6), you must put the tag by itself on the first line (and it must be complete):

Example 162Try It

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

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

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

Example 163Try It

    <Warning>
    *bar*
    </Warning>

    <Warning>
    *bar*
    </Warning>

Example 164Try It

    <i class="foo">
    *bar*
    </i>

    <i class="foo">
    *bar*
    </i>

Example 165Try It

    </ins>
    *bar*

    </ins>
    *bar*

These rules are designed to allow us to work with tags that can function as either block-level or inline-level tags. The `<del>` tag is a nice example. We can surround content with `<del>` tags in three different ways. In this case, we get a raw HTML block, because the `<del>` tag is on a line by itself:

Example 166Try It

    <del>
    *foo*
    </del>

    <del>
    *foo*
    </del>

In this case, we get a raw HTML block that just includes the `<del>` tag (because it ends with the following blank line). So the contents get interpreted as CommonMark:

Example 167Try It

    <del>

    *foo*

    </del>

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

Finally, in this case, the `<del>` tags are interpreted as raw HTML inside the CommonMark paragraph. (Because the tag is not on a line by itself, we get inline HTML rather than an HTML block.)

Example 168Try It

    <del>*foo*</del>

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

HTML tags designed to contain literal content (`pre`, `script`, `style`, `textarea`), comments, processing instructions, and declarations are treated somewhat differently. Instead of ending at the first blank line, these blocks end at the first line containing a corresponding end tag. As a result, these blocks can contain blank lines:

A pre tag (type 1):

Example 169Try It

    <pre language="haskell"><code>
    import Text.HTML.TagSoup

    main :: IO ()
    main = print $ parseTags tags
    </code></pre>
    okay

    <pre language="haskell"><code>
    import Text.HTML.TagSoup

    main :: IO ()
    main = print $ parseTags tags
    </code></pre>
    <p>okay</p>

A script tag (type 1):

Example 170Try It

    <script type="text/javascript">
    // JavaScript example

    document.getElementById("demo").innerHTML = "Hello JavaScript!";
    </script>
    okay

    <script type="text/javascript">
    // JavaScript example

    document.getElementById("demo").innerHTML = "Hello JavaScript!";
    </script>
    <p>okay</p>

A textarea tag (type 1):

Example 171Try It

    <textarea>

    *foo*

    _bar_

    </textarea>

    <textarea>

    *foo*

    _bar_

    </textarea>

A style tag (type 1):

Example 172Try It

    <style
      type="text/css">
    h1 {color:red;}

    p {color:blue;}
    </style>
    okay

    <style
      type="text/css">
    h1 {color:red;}

    p {color:blue;}
    </style>
    <p>okay</p>

If there is no matching end tag, the block will end at the end of the document (or the enclosing block quote or list item):

Example 173Try It

    <style
      type="text/css">

    foo

    <style
      type="text/css">

    foo

Example 174Try It

    > <div>
    > foo

    bar

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

Example 175Try It

    - <div>
    - foo

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

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

Example 176Try It

    <style>p{color:red;}</style>
    *foo*

    <style>p{color:red;}</style>
    <p><em>foo</em></p>

Example 177Try It

    <!-- foo -->*bar*
    *baz*

    <!-- foo -->*bar*
    <p><em>baz</em></p>

Note that anything on the last line after the end tag will be included in the HTML block:

Example 178Try It

    <script>
    foo
    </script>1. *bar*

    <script>
    foo
    </script>1. *bar*

A comment (type 2):

Example 179Try It

    <!-- Foo

    bar
       baz -->
    okay

    <!-- Foo

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

A processing instruction (type 3):

Example 180Try It

    <?php

      echo '>';

    ?>
    okay

    <?php

      echo '>';

    ?>
    <p>okay</p>

A declaration (type 4):

Example 181Try It

    <!DOCTYPE html>

    <!DOCTYPE html>

CDATA (type 5):

Example 182Try It

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

      } else {

        return 0;
      }
    }
    ]]>
    okay

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

      } else {

        return 0;
      }
    }
    ]]>
    <p>okay</p>

The opening tag can be preceded by up to three spaces of indentation, but not four:

Example 183Try It

      <!-- foo -->

        <!-- foo -->

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

Example 184Try It

      <div>

        <div>

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

An HTML block of types 1–6 can interrupt a paragraph, and need not be preceded by a blank line.

Example 185Try It

    Foo
    <div>
    bar
    </div>

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

However, a following blank line is needed, except at the end of a document, and except for blocks of types 1–5, above:

Example 186Try It

    <div>
    bar
    </div>
    *foo*

    <div>
    bar
    </div>
    *foo*

HTML blocks of type 7 cannot interrupt a paragraph:

Example 187Try It

    Foo
    <a href="bar">
    baz

    <p>Foo
    <a href="bar">
    baz</p>

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

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

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

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

Most Markdown implementations (including some of Gruber’s own) do not respect all of these restrictions.

There is one respect, however, in which Gruber’s rule is more liberal than the one given here, since it allows blank lines to occur inside an HTML block. There are two reasons for disallowing them here. First, it removes the need to parse balanced tags, which is expensive and can require backtracking from the end of the document if no matching end tag is found. Second, it provides a very simple and flexible way of including Markdown content inside HTML tags: simply separate the Markdown from the HTML using blank lines:

Compare:

Example 188Try It

    <div>

    *Emphasized* text.

    </div>

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

Example 189Try It

    <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 190Try It

    <table>

    <tr>

    <td>
    Hi
    </td>

    </tr>

    </table>

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

There are problems, however, if the inner tags are indented and separated by spaces, as then they will be interpreted as an indented code block:

Example 191Try It

    <table>

      <tr>

        <td>
          Hi
        </td>

      </tr>

    </table>

    <table>
      <tr>
    <pre><code>&lt;td&gt;
      Hi
    &lt;/td&gt;
    </code></pre>
      </tr>
    </table>

Fortunately, blank lines are usually not necessary and can be deleted. The exception is inside `<pre>` tags, but as described above, raw HTML blocks starting with `<pre>` can contain blank lines.

## 4.7Link reference definitions

A link reference definition consists of a link label, optionally preceded by up to three spaces of indentation, followed by a colon (`:`), optional spaces or tabs (including up to one line ending), a link destination, optional spaces or tabs (including up to one line ending), and an optional link title, which if it is present must be separated from the link destination by spaces or tabs. No further character may occur.

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 192Try It

    [foo]: /url "title"

    [foo]

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

Example 193Try It

       [foo]:
          /url
               'the title'

    [foo]

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

Example 194Try It

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

    [Foo*bar\]]

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

Example 195Try It

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

    [Foo bar]

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

The title may extend over multiple lines:

Example 196Try It

    [foo]: /url '
    title
    line1
    line2
    '

    [foo]

    <p><a href="/url" title="
    title
    line1
    line2
    ">foo</a></p>

However, it may not contain a blank line:

Example 197Try It

    [foo]: /url 'title

    with blank line'

    [foo]

    <p>[foo]: /url 'title</p>
    <p>with blank line'</p>
    <p>[foo]</p>

The title may be omitted:

Example 198Try It

    [foo]:
    /url

    [foo]

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

The link destination may not be omitted:

Example 199Try It

    [foo]:

    [foo]

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

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

Example 200Try It

    [foo]: <>

    [foo]

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

The title must be separated from the link destination by spaces or tabs:

Example 201Try It

    [foo]: <bar>(baz)

    [foo]

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

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

Example 202Try It

    [foo]: /url\bar\*baz "foo\"bar\baz"

    [foo]

    <p><a href="/url%5Cbar*baz" title="foo&quot;bar\baz">foo</a></p>

A link can come before its corresponding definition:

Example 203Try It

    [foo]

    [foo]: url

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

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

Example 204Try It

    [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 205Try It

    [FOO]: /url

    [Foo]

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

Example 206Try It

    [ΑΓΩ]: /φου

    [αγω]

    <p><a href="/%CF%86%CE%BF%CF%85">αγω</a></p>

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

Example 207Try It

    [foo]: /url

Here is another one:

Example 208Try It

    [
    foo
    ]: /url
    bar

    <p>bar</p>

This is not a link reference definition, because there are characters other than spaces or tabs after the title:

Example 209Try It

    [foo]: /url "title" ok

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

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

Example 210Try It

    [foo]: /url
    "title" ok

    <p>&quot;title&quot; ok</p>

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

Example 211Try It

        [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 212Try It

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

    [foo]

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

A link reference definition cannot interrupt a paragraph.

Example 213Try It

    Foo
    [bar]: /baz

    [bar]

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

However, it can directly follow other block elements, such as headings and thematic breaks, and it need not be followed by a blank line.

Example 214Try It

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

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

Example 215Try It

    [foo]: /url
    bar
    ===
    [foo]

    <h1>bar</h1>
    <p><a href="/url">foo</a></p>

Example 216Try It

    [foo]: /url
    ===
    [foo]

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

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

Example 217Try It

    [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 218Try It

    [foo]

    > [foo]: /url

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

## 4.8Paragraphs

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 or tabs.

A simple example with two paragraphs:

Example 219Try It

    aaa

    bbb

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

Paragraphs can contain multiple lines, but no blank lines:

Example 220Try It

    aaa
    bbb

    ccc
    ddd

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

Multiple blank lines between paragraphs have no effect:

Example 221Try It

    aaa

    bbb

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

Leading spaces or tabs are skipped:

Example 222Try It

      aaa
     bbb

    <p>aaa
    bbb</p>

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

Example 223Try It

    aaa
                 bbb
                                           ccc

    <p>aaa
    bbb
    ccc</p>

However, the first line may be preceded by up to three spaces of indentation. Four spaces of indentation is too many:

Example 224Try It

       aaa
    bbb

    <p>aaa
    bbb</p>

Example 225Try It

        aaa
    bbb

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

Final spaces or tabs are stripped before inline parsing, so a paragraph that ends with two or more spaces will not end with a hard line break:

Example 226Try It

    aaa
    bbb

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

## 4.9Blank 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 227Try It

    aaa

    # aaa

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

# 5Container 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.)

## 5.1Block quotes

A block quote marker, optionally preceded by up to three spaces of indentation, consists of (a) the character `>` together with a following space of indentation, or (b) a single character `>` not followed by a space of indentation.

The following rules define block quotes:

1. Basic case. If a string of lines Ls constitute a sequence of blocks Bs, then the result of prepending a block quote marker to the beginning of each line in Ls is a block quote containing Bs.

2. Laziness. If a string of lines Ls constitute a block quote with contents Bs, then the result of deleting the initial block quote marker from one or more lines in which the next character other than a space or tab after the block quote marker is paragraph continuation text is a block quote with Bs as its content. Paragraph continuation text is text that will be parsed as part of the content of a paragraph, but does not occur at the beginning of the paragraph.

3. Consecutiveness. A document cannot contain two block quotes in a row unless there is a blank line between them.

Nothing else counts as a block quote.

Here is a simple example:

Example 228Try It

    > # Foo
    > bar
    > baz

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

The space or tab after the `>` characters can be omitted:

Example 229Try It

    ># Foo
    >bar
    > baz

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

The `>` characters can be preceded by up to three spaces of indentation:

Example 230Try It

       > # Foo
       > bar
     > baz

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

Four spaces of indentation is too many:

Example 231Try It

        > # Foo
        > bar
        > baz

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

The Laziness clause allows us to omit the `>` before paragraph continuation text:

Example 232Try It

    > # 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 233Try It

    > bar
    baz
    > foo

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

Laziness only applies to lines that would have been continuations of paragraphs had they been prepended with block quote markers. For example, the `>` cannot be omitted in the second line of

    > foo
    > ---

without changing the meaning:

Example 234Try It

    > foo
    ---

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

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

    > - foo
    > - bar

then the block quote ends after the first line:

Example 235Try It

    > - foo
    - bar

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

For the same reason, we can’t omit the `>` in front of subsequent lines of an indented or fenced code block:

Example 236Try It

    >     foo
        bar

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

Example 237Try It

    > ```
    foo
    ```

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

Note that in the following case, we have a lazy continuation line:

Example 238Try It

    > foo
        - bar

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

To see why, note that in

    > foo
    >     - bar

the `- bar` is indented too far to start a list, and can’t be an indented code block because indented code blocks cannot interrupt paragraphs, so it is paragraph continuation text.

A block quote can be empty:

Example 239Try It

    >

    <blockquote>
    </blockquote>

Example 240Try It

    >
    >
    >

    <blockquote>
    </blockquote>

A block quote can have initial or final blank lines:

Example 241Try It

    >
    > foo
    >

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

A blank line always separates block quotes:

Example 242Try It

    > 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 243Try It

    > foo
    > bar

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

To get a block quote with two paragraphs, use:

Example 244Try It

    > foo
    >
    > bar

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

Block quotes can interrupt paragraphs:

Example 245Try It

    foo
    > bar

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

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

Example 246Try It

    > 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 247Try It

    > bar
    baz

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

Example 248Try It

    > bar

    baz

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

Example 249Try It

    > 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 250Try It

    > > > foo
    bar

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

Example 251Try It

    >>> 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 of indentation. So five spaces are needed after the `>`:

Example 252Try It

    >     code

    >    not code

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

## 5.2List items

A list marker is a bullet list marker or an ordered list marker.

A bullet list marker is a `-`, `+`, or `*` character.

An ordered list marker is a sequence of 1–9 arabic digits (`0-9`), followed by either a `.` character or a `)` character. (The reason for the length limit is that with 10 digits we start seeing integer overflows in some browsers.)

The following rules define list items:

1. Basic case. If a sequence of lines Ls constitute a sequence of blocks Bs starting with a character other than a space or tab, and M is a list marker of width W followed by 1 ≤ N ≤ 4 spaces of indentation, then the result of prepending M and the following spaces to the first line of Ls, and indenting subsequent lines of Ls by W + N spaces, is a list item with Bs as its contents. The type of the list item (bullet or ordered) is determined by the type of its list marker. If the list item is ordered, then it is also assigned a start number, based on the ordered list marker.

   Exceptions:

   1. When the first list item in a list interrupts a paragraph—that is, when it starts on a line that would otherwise count as paragraph continuation text—then (a) the lines Ls must not begin with a blank line, and (b) if the list item is ordered, the start number must be 1.
   2. If any line is a thematic break then that line is not a list item.

For example, let Ls be the lines

Example 253Try It

    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 254Try It

    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 of indentation, and there are three spaces between the list marker and the next character other than a space or tab, 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 255Try It

    - one

     two

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

Example 256Try It

    - one

      two

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

Example 257Try It

     -    one

         two

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

Example 258Try It

     -    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 character other than a space or tab after the list marker. However, that is not quite right. The spaces of indentation 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 259Try It

       > > 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 260Try It

    >>- one
    >>
      >  > two

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

Note that at least one space or tab is needed between the list marker and any following content, so these are not list items:

Example 261Try It

    -one

    2.two

    <p>-one</p>
    <p>2.two</p>

A list item may contain blocks that are separated by more than one blank line.

Example 262Try It

    - foo

      bar

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

A list item may contain any kind of block:

Example 263Try It

    1.  foo

        ```
        bar
        ```

        baz

        > bam

    <ol>
    <li>
    <p>foo</p>
    <pre><code>bar
    </code></pre>
    <p>baz</p>
    <blockquote>
    <p>bam</p>
    </blockquote>
    </li>
    </ol>

A list item that contains an indented code block will preserve empty lines within the code block verbatim.

Example 264Try It

    - Foo

          bar

          baz

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

    baz
    </code></pre>
    </li>
    </ul>

Note that ordered list start numbers must be nine digits or less:

Example 265Try It

    123456789. ok

    <ol start="123456789">
    <li>ok</li>
    </ol>

Example 266Try It

    1234567890. not ok

    <p>1234567890. not ok</p>

A start number may begin with 0s:

Example 267Try It

    0. ok

    <ol start="0">
    <li>ok</li>
    </ol>

Example 268Try It

    003. ok

    <ol start="3">
    <li>ok</li>
    </ol>

A start number may not be negative:

Example 269Try It

    -1. not ok

    <p>-1. not ok</p>

2. Item starting with indented code. If a sequence of lines Ls constitute a sequence of blocks Bs starting with an indented code block, and M is a list marker of width W followed by one space of indentation, 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 preceded by four spaces of indentation beyond the edge of the region where text will be included in the list item. In the following case that is 6 spaces:

Example 270Try It

    - foo

          bar

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

And in this case it is 11 spaces:

Example 271Try It

      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 preceded by one space of indentation after the list marker:

Example 272Try It

        indented code

    paragraph

        more code

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

Example 273Try It

    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 of indentation is interpreted as space inside the code block:

Example 274Try It

    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 character other than a space or tab, and (b) cases in which they begin with an indented code block. In a case like the following, where the first block begins with three spaces of indentation, the rules do not allow us to form a list item by indenting the whole thing and prepending a list marker:

Example 275Try It

       foo

    bar

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

Example 276Try It

    -    foo

      bar

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

This is not a significant restriction, because when a block is preceded by up to three spaces of indentation, the indentation can always be removed without a change in interpretation, allowing rule #1 to be applied. So, in the above case:

Example 277Try It

    -  foo

       bar

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

3. Item starting with a blank line. If a sequence of lines Ls starting with a single blank line constitute a (possibly empty) sequence of blocks Bs, and M is a list marker of width W, then the result of prepending M to the first line of Ls, and preceding subsequent lines of Ls by W + 1 spaces of indentation, is a list item with Bs as its contents. If a line is empty, then it need not be indented. The type of the list item (bullet or ordered) is determined by the type of its list marker. If the list item is ordered, then it is also assigned a start number, based on the ordered list marker.

Here are some list items that start with a blank line but are not empty:

Example 278Try It

    -
      foo
    -
      ```
      bar
      ```
    -
          baz

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

When the list item starts with a blank line, the number of spaces following the list marker doesn’t change the required indentation:

Example 279Try It

    -
      foo

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

A list item can begin with at most one blank line. In the following example, `foo` is not part of the list item:

Example 280Try It

    -

      foo

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

Here is an empty bullet list item:

Example 281Try It

    - foo
    -
    - bar

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

It does not matter whether there are spaces or tabs following the list marker:

Example 282Try It

    - foo
    -
    - bar

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

Here is an empty ordered list item:

Example 283Try It

    1. foo
    2.
    3. bar

    <ol>
    <li>foo</li>
    <li></li>
    <li>bar</li>
    </ol>

A list may start or end with an empty list item:

Example 284Try It

    *

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

However, an empty list item cannot interrupt a paragraph:

Example 285Try It

    foo
    *

    foo
    1.

    <p>foo
    *</p>
    <p>foo
    1.</p>

4. Indentation. If a sequence of lines Ls constitutes a list item according to rule #1, #2, or #3, then the result of preceding each line of Ls by up to three spaces of indentation (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 286Try It

     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 287Try It

      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 288Try It

       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 289Try It

        1.  A paragraph
            with two lines.

                indented code

            > A block quote.

    <pre><code>1.  A paragraph
        with two lines.

            indented code

        &gt; A block quote.
    </code></pre>

5. Laziness. If a string of lines Ls constitute a list item with contents Bs, then the result of deleting some or all of the indentation from one or more lines in which the next character other than a space or tab after the indentation is paragraph continuation text is a list item with the same contents and attributes. The unindented lines are called lazy continuation lines.

Here is an example with lazy continuation lines:

Example 290Try It

      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 291Try It

      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 292Try It

    > 1. > Blockquote
    continued here.

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

Example 293Try It

    > 1. > Blockquote
    > continued here.

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

6. That’s all. Nothing that is not counted as a list item by rules #1–5 counts as a list item.

The rules for sublists follow from the general rules above. A sublist must be indented the same number of spaces of indentation 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 294Try It

    - foo
      - bar
        - baz
          - boo

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

One is not enough:

Example 295Try It

    - foo
     - bar
      - baz
       - boo

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

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

Example 296Try It

    10) foo
        - bar

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

Three is not enough:

Example 297Try It

    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 298Try It

    - - foo

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

Example 299Try It

    1. - 2. foo

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

A list item can contain a heading:

Example 300Try It

    - # Foo
    - Bar
      ---
      baz

    <ul>
    <li>
    <h1>Foo</h1>
    </li>
    <li>
    <h2>Bar</h2>
    baz</li>
    </ul>

### 5.2.1Motivation

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

1. “List markers typically start at the left margin, but may be indented by up to three spaces. List markers must be followed by one or more spaces or a tab.”

2. “To make lists look nice, you can wrap items with hanging indents…. But if you don’t want to, you don’t have to.”

3. “List items may consist of multiple paragraphs. Each subsequent paragraph in a list item must be indented by either 4 spaces or one tab.”

4. “It looks nice if you indent every line of the subsequent paragraphs, but here again, Markdown will allow you to be lazy.”

5. “To put a blockquote within a list item, the blockquote’s `>` delimiters need to be indented.”

6. “To put a code block within a list item, the code block needs to be indented twice — 8 spaces or two tabs.”

These rules specify that a paragraph under a list item must be indented four spaces (presumably, from the left margin, rather than the start of the list marker, but this is not said), and that code under a list item must be indented eight spaces instead of the usual four. They also say that a block quote must be indented, but not by how much; however, the example given has four spaces indentation. Although nothing is said about other kinds of block-level content, it is certainly reasonable to infer that all block elements under a list item, including other lists, must be indented four spaces. This principle has been called the four-space rule.

The four-space rule is clear and principled, and if the reference implementation `Markdown.pl` had followed it, it probably would have become the standard. However, `Markdown.pl` allowed paragraphs and sublists to start with only two spaces indentation, at least on the outer level. Worse, its behavior was inconsistent: a sublist of an outer-level list needed two spaces indentation, but a sublist of this sublist needed three spaces. It is not surprising, then, that different implementations of Markdown have developed very different rules for determining what comes under a list item. (Pandoc and python-Markdown, for example, stuck with Gruber’s syntax description and the four-space rule, while discount, redcarpet, marked, PHP Markdown, and others followed `Markdown.pl`’s behavior more closely.)

Unfortunately, given the divergences between implementations, there is no way to give a spec for list items that will be guaranteed not to break any existing documents. However, the spec given here should correctly handle lists formatted with either the four-space rule or the more forgiving `Markdown.pl` behavior, provided they are laid out in a way that is natural for a human to read.

The strategy here is to let the width and indentation of the list marker determine the indentation necessary for blocks to fall under the list item, rather than having a fixed and arbitrary number. The writer can think of the body of the list item as a unit which gets indented to the right enough to fit the list marker (and any indentation on the list marker). (The laziness rule, #5, then allows continuation lines to be unindented if needed.)

This rule is superior, we claim, to any rule requiring a fixed level of indentation from the margin. The four-space rule is clear but unnatural. It is quite unintuitive that

    - foo

      bar

      - baz

should be parsed as two lists with an intervening paragraph,

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

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

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

The choice of four spaces is arbitrary. It can be learned, but it is not likely to be guessed, and it trips up beginners regularly.

Would it help to adopt a two-space rule? The problem is that such a rule, together with the rule allowing up to three spaces of indentation for the initial list marker, allows text that is indented less than the original list marker to be included in the list item. For example, `Markdown.pl` parses

       - one

      two

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

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

and similarly

    >   - one
    >
    >  two

as

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

This is extremely unintuitive.

Rather than requiring a fixed indent from the margin, we could require a fixed indent (say, two spaces, or even one space) from the list marker (which may itself be indented). This proposal would remove the last anomaly discussed. Unlike the spec presented above, it would count the following as a list item with a subparagraph, even though the paragraph `bar` is not indented as far as the first paragraph `foo`:

     10. foo

       bar

Arguably this text does read like a list item with `bar` as a subparagraph, which may count in favor of the proposal. However, on this proposal indented code would have to be indented six spaces after the list marker. And this would break a lot of existing Markdown, which has the pattern:

    1.  foo

            indented code

where the code is indented eight spaces. The spec above, by contrast, will parse this text as expected, since the code block’s indentation is measured from the beginning of `foo`.

The one case that needs special treatment is a list item that starts with indented code. How much indentation is required in that case, since we don’t have a “first paragraph” to measure from? Rule #2 simply stipulates that in such cases, we require one space indentation from the list marker (and then the normal four spaces for the indented code). This will match the four-space rule in cases where the list marker plus its initial indentation takes four spaces (a common case), but diverge in other cases.

## 5.3Lists

A list is a sequence of one or more list items of the same type. The list items may be separated by any number of blank lines.

Two list items are of the same type if they begin with a list marker of the same type. Two list markers are of the same type if (a) they are bullet list markers using the same character (`-`, `+`, or `*`) or (b) they are ordered list numbers with the same delimiter (either `.` or `)`).

A list is an ordered list if its constituent list items begin with ordered list markers, and a bullet list if its constituent list items begin with bullet list markers.

The start number of an ordered list is determined by the list number of its initial list item. The numbers of subsequent list items are disregarded.

A list is loose if any of its constituent list items are separated by blank lines, or if any of its constituent list items directly contain two block-level elements with a blank line between them. Otherwise a list is tight. (The difference in HTML output is that paragraphs in a loose list are wrapped in `<p>` tags, while paragraphs in a tight list are not.)

Changing the bullet or ordered list delimiter starts a new list:

Example 301Try It

    - foo
    - bar
    + baz

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

Example 302Try It

    1. foo
    2. bar
    3) baz

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

In CommonMark, a list can interrupt a paragraph. That is, no blank line is needed to separate a paragraph from a following list:

Example 303Try It

    Foo
    - bar
    - baz

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

`Markdown.pl` does not allow this, through fear of triggering a list via a numeral in a hard-wrapped line:

    The number of windows in my house is
    14.  The number of doors is 6.

Oddly, though, `Markdown.pl` does allow a blockquote to interrupt a paragraph, even though the same considerations might apply.

In CommonMark, we do allow lists to interrupt paragraphs, for two reasons. First, it is natural and not uncommon for people to start lists without blank lines:

    I need to buy
    - new shoes
    - a coat
    - a plane ticket

Second, we are attracted to a

> principle of uniformity: if a chunk of text has a certain meaning, it will continue to have the same meaning when put into a container block (such as a list item or blockquote).

(Indeed, the spec for list items and block quotes presupposes this principle.) This principle implies that if

      * I need to buy
        - new shoes
        - a coat
        - a plane ticket

is a list item containing a paragraph followed by a nested sublist, as all Markdown implementations agree it is (though the paragraph may be rendered without `<p>` tags, since the list is “tight”), then

    I need to buy
    - new shoes
    - a coat
    - a plane ticket

by itself should be a paragraph followed by a nested sublist.

Since it is well established Markdown practice to allow lists to interrupt paragraphs inside list items, the principle of uniformity requires us to allow this outside list items as well. (reStructuredText takes a different approach, requiring blank lines before lists even inside other list items.)

In order to solve the problem of unwanted lists in paragraphs with hard-wrapped numerals, we allow only lists starting with `1` to interrupt paragraphs. Thus,

Example 304Try It

    The number of windows in my house is
    14.  The number of doors is 6.

    <p>The number of windows in my house is
    14.  The number of doors is 6.</p>

We may still get an unintended result in cases like

Example 305Try It

    The number of windows in my house is
    1.  The number of doors is 6.

    <p>The number of windows in my house is</p>
    <ol>
    <li>The number of doors is 6.</li>
    </ol>

but this rule should prevent most spurious list captures.

There can be any number of blank lines between items:

Example 306Try It

    - foo

    - bar

    - baz

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

Example 307Try It

    - foo
      - bar
        - baz

          bim

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

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

Example 308Try It

    - foo
    - bar

    <!-- -->

    - baz
    - bim

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

Example 309Try It

    -   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 310Try It

    - a
     - b
      - c
       - d
      - e
     - f
    - g

    <ul>
    <li>a</li>
    <li>b</li>
    <li>c</li>
    <li>d</li>
    <li>e</li>
    <li>f</li>
    <li>g</li>
    </ul>

Example 311Try It

    1. a

      2. b

       3. c

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

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

Example 312Try It

    - a
     - b
      - c
       - d
        - e

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

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

Example 313Try It

    1. a

      2. b

        3. c

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

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

Example 314Try It

    - 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 315Try It

    * a
    *

    * c

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

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

Example 316Try It

    - 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 317Try It

    - 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 318Try It

    - a
    - ```
      b

      ```
    - c

    <ul>
    <li>a</li>
    <li>
    <pre><code>b

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

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

Example 319Try It

    - 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 320Try It

    * 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 321Try It

    - 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 322Try It

    - a

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

Example 323Try It

    - a
      - b

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

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

Example 324Try It

    1. ```
       foo
       ```

       bar

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

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

Example 325Try It

    * foo
      * bar

      baz

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

Example 326Try It

    - 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>

# 6Inlines

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 327Try It

    `hi`lo`

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

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

## 6.1Code spans

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

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

- First, line endings are converted to spaces.
- If the resulting string both begins and ends with a space character, but does not consist entirely of space characters, a single space character is removed from the front and back. This allows you to include code that begins or ends with backtick characters, which must be separated by whitespace from the opening or closing backtick strings.

This is a simple code span:

Example 328Try It

    `foo`

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

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

Example 329Try It

    `` foo ` bar ``

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

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

Example 330Try It

    ` `` `

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

Note that only one space is stripped:

Example 331Try It

    `  ``  `

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

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

Example 332Try It

    ` a`

    <p><code> a</code></p>

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

Example 333Try It

    ` b `

    <p><code> b </code></p>

No stripping occurs if the code span contains only spaces:

Example 334Try It

    ` `
    `  `

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

Line endings are treated like spaces:

Example 335Try It

    ``
    foo
    bar
    baz
    ``

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

Example 336Try It

    ``
    foo
    ``

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

Interior spaces are not collapsed:

Example 337Try It

    `foo   bar
    baz`

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

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

    code{white-space: pre-wrap;}

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

Example 338Try It

    `foo\`bar`

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

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

Example 339Try It

    ``foo`bar``

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

Example 340Try It

    ` foo `` bar `

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

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

Example 341Try It

    *foo`*`

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

And this is not parsed as a link:

Example 342Try It

    [not a `link](/foo`)

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

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

Example 343Try It

    `<a href="`">`

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

But this is an HTML tag:

Example 344Try It

    <a href="`">`

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

And this is code:

Example 345Try It

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

    <p><code>&lt;https://foo.bar.</code>baz&gt;`</p>

But this is an autolink:

Example 346Try It

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

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

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

Example 347Try It

    ```foo``

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

Example 348Try It

    `foo

    <p>`foo</p>

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

Example 349Try It

    `foo``bar``

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

## 6.2Emphasis and strong emphasis

John Gruber’s original Markdown syntax description says:

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

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

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

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

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

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

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

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

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

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

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

Here are some examples of delimiter runs.

- left-flanking but not right-flanking:

      ***abc
        _abc
      **"abc"
       _"abc"

- right-flanking but not left-flanking:

       abc***
       abc_
      "abc"**
      "abc"_

- Both left and right-flanking:

       abc***def
      "abc"_"def"

- Neither left nor right-flanking:

      abc *** def
      a _ b

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

The following rules define emphasis and strong emphasis:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

These rules can be illustrated through a series of examples.

Rule 1:

Example 350Try It

    *foo bar*

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

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

Example 351Try It

    a * foo bar*

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

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

Example 352Try It

    a*"foo"*

    <p>a*&quot;foo&quot;*</p>

Unicode nonbreaking spaces count as whitespace, too:

Example 353Try It

    * a *

    <p>* a *</p>

Unicode symbols count as punctuation, too:

Example 354Try It

    *$*alpha.

    *£*bravo.

    *€*charlie.

    <p>*$*alpha.</p>
    <p>*£*bravo.</p>
    <p>*€*charlie.</p>

Intraword emphasis with `*` is permitted:

Example 355Try It

    foo*bar*

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

Example 356Try It

    5*6*78

    <p>5<em>6</em>78</p>

Rule 2:

Example 357Try It

    _foo bar_

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

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

Example 358Try It

    _ foo bar_

    <p>_ foo bar_</p>

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

Example 359Try It

    a_"foo"_

    <p>a_&quot;foo&quot;_</p>

Emphasis with `_` is not allowed inside words:

Example 360Try It

    foo_bar_

    <p>foo_bar_</p>

Example 361Try It

    5_6_78

    <p>5_6_78</p>

Example 362Try It

    пристаням_стремятся_

    <p>пристаням_стремятся_</p>

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

Example 363Try It

    aa_"bb"_cc

    <p>aa_&quot;bb&quot;_cc</p>

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

Example 364Try It

    foo-_(bar)_

    <p>foo-<em>(bar)</em></p>

Rule 3:

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

Example 365Try It

    _foo*

    <p>_foo*</p>

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

Example 366Try It

    *foo bar *

    <p>*foo bar *</p>

A line ending also counts as whitespace:

Example 367Try It

    *foo bar
    *

    <p>*foo bar
    *</p>

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

Example 368Try It

    *(*foo)

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

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

Example 369Try It

    *(*foo*)*

    <p><em>(<em>foo</em>)</em></p>

Intraword emphasis with `*` is allowed:

Example 370Try It

    *foo*bar

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

Rule 4:

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

Example 371Try It

    _foo bar _

    <p>_foo bar _</p>

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

Example 372Try It

    _(_foo)

    <p>_(_foo)</p>

This is emphasis within emphasis:

Example 373Try It

    _(_foo_)_

    <p><em>(<em>foo</em>)</em></p>

Intraword emphasis is disallowed for `_`:

Example 374Try It

    _foo_bar

    <p>_foo_bar</p>

Example 375Try It

    _пристаням_стремятся

    <p>_пристаням_стремятся</p>

Example 376Try It

    _foo_bar_baz_

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

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

Example 377Try It

    _(bar)_.

    <p><em>(bar)</em>.</p>

Rule 5:

Example 378Try It

    **foo bar**

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

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

Example 379Try It

    ** foo bar**

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

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

Example 380Try It

    a**"foo"**

    <p>a**&quot;foo&quot;**</p>

Intraword strong emphasis with `**` is permitted:

Example 381Try It

    foo**bar**

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

Rule 6:

Example 382Try It

    __foo bar__

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

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

Example 383Try It

    __ foo bar__

    <p>__ foo bar__</p>

A line ending counts as whitespace:

Example 384Try It

    __
    foo bar__

    <p>__
    foo bar__</p>

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

Example 385Try It

    a__"foo"__

    <p>a__&quot;foo&quot;__</p>

Intraword strong emphasis is forbidden with `__`:

Example 386Try It

    foo__bar__

    <p>foo__bar__</p>

Example 387Try It

    5__6__78

    <p>5__6__78</p>

Example 388Try It

    пристаням__стремятся__

    <p>пристаням__стремятся__</p>

Example 389Try It

    __foo, __bar__, baz__

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

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

Example 390Try It

    foo-__(bar)__

    <p>foo-<strong>(bar)</strong></p>

Rule 7:

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

Example 391Try It

    **foo bar **

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

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

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

Example 392Try It

    **(**foo)

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

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

Example 393Try It

    *(**foo**)*

    <p><em>(<strong>foo</strong>)</em></p>

Example 394Try It

    **Gomphocarpus (*Gomphocarpus physocarpus*, syn.
    *Asclepias physocarpa*)**

    <p><strong>Gomphocarpus (<em>Gomphocarpus physocarpus</em>, syn.
    <em>Asclepias physocarpa</em>)</strong></p>

Example 395Try It

    **foo "*bar*" foo**

    <p><strong>foo &quot;<em>bar</em>&quot; foo</strong></p>

Intraword emphasis:

Example 396Try It

    **foo**bar

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

Rule 8:

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

Example 397Try It

    __foo bar __

    <p>__foo bar __</p>

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

Example 398Try It

    __(__foo)

    <p>__(__foo)</p>

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

Example 399Try It

    _(__foo__)_

    <p><em>(<strong>foo</strong>)</em></p>

Intraword strong emphasis is forbidden with `__`:

Example 400Try It

    __foo__bar

    <p>__foo__bar</p>

Example 401Try It

    __пристаням__стремятся

    <p>__пристаням__стремятся</p>

Example 402Try It

    __foo__bar__baz__

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

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

Example 403Try It

    __(bar)__.

    <p><strong>(bar)</strong>.</p>

Rule 9:

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

Example 404Try It

    *foo [bar](/url)*

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

Example 405Try It

    *foo
    bar*

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

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

Example 406Try It

    _foo __bar__ baz_

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

Example 407Try It

    _foo _bar_ baz_

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

Example 408Try It

    __foo_ bar_

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

Example 409Try It

    *foo *bar**

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

Example 410Try It

    *foo **bar** baz*

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

Example 411Try It

    *foo**bar**baz*

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

Note that in the preceding case, the interpretation

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

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

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

Example 412Try It

    *foo**bar*

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

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

Example 413Try It

    ***foo** bar*

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

Example 414Try It

    *foo **bar***

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

Example 415Try It

    *foo**bar***

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

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

Example 416Try It

    foo***bar***baz

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

Example 417Try It

    foo******bar*********baz

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

Indefinite levels of nesting are possible:

Example 418Try It

    *foo **bar *baz* bim** bop*

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

Example 419Try It

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

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

There can be no empty emphasis or strong emphasis:

Example 420Try It

    ** is not an empty emphasis

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

Example 421Try It

    **** is not an empty strong emphasis

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

Rule 10:

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

Example 422Try It

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

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

Example 423Try It

    **foo
    bar**

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

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

Example 424Try It

    __foo _bar_ baz__

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

Example 425Try It

    __foo __bar__ baz__

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

Example 426Try It

    ____foo__ bar__

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

Example 427Try It

    **foo **bar****

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

Example 428Try It

    **foo *bar* baz**

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

Example 429Try It

    **foo*bar*baz**

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

Example 430Try It

    ***foo* bar**

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

Example 431Try It

    **foo *bar***

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

Indefinite levels of nesting are possible:

Example 432Try It

    **foo *bar **baz**
    bim* bop**

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

Example 433Try It

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

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

There can be no empty emphasis or strong emphasis:

Example 434Try It

    __ is not an empty emphasis

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

Example 435Try It

    ____ is not an empty strong emphasis

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

Rule 11:

Example 436Try It

    foo ***

    <p>foo ***</p>

Example 437Try It

    foo *\**

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

Example 438Try It

    foo *_*

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

Example 439Try It

    foo *****

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

Example 440Try It

    foo **\***

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

Example 441Try It

    foo **_**

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

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

Example 442Try It

    **foo*

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

Example 443Try It

    *foo**

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

Example 444Try It

    ***foo**

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

Example 445Try It

    ****foo*

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

Example 446Try It

    **foo***

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

Example 447Try It

    *foo****

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

Rule 12:

Example 448Try It

    foo ___

    <p>foo ___</p>

Example 449Try It

    foo _\__

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

Example 450Try It

    foo _*_

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

Example 451Try It

    foo _____

    <p>foo _____</p>

Example 452Try It

    foo __\___

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

Example 453Try It

    foo __*__

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

Example 454Try It

    __foo_

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

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

Example 455Try It

    _foo__

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

Example 456Try It

    ___foo__

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

Example 457Try It

    ____foo_

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

Example 458Try It

    __foo___

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

Example 459Try It

    _foo____

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

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

Example 460Try It

    **foo**

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

Example 461Try It

    *_foo_*

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

Example 462Try It

    __foo__

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

Example 463Try It

    _*foo*_

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

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

Example 464Try It

    ****foo****

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

Example 465Try It

    ____foo____

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

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

Example 466Try It

    ******foo******

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

Rule 14:

Example 467Try It

    ***foo***

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

Example 468Try It

    _____foo_____

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

Rule 15:

Example 469Try It

    *foo _bar* baz_

    <p><em>foo _bar</em> baz_</p>

Example 470Try It

    *foo __bar *baz bim__ bam*

    <p><em>foo <strong>bar *baz bim</strong> bam</em></p>

Rule 16:

Example 471Try It

    **foo **bar baz**

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

Example 472Try It

    *foo *bar baz*

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

Rule 17:

Example 473Try It

    *[bar*](/url)

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

Example 474Try It

    _foo [bar_](/url)

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

Example 475Try It

    *<img src="foo" title="*"/>

    <p>*<img src="foo" title="*"/></p>

Example 476Try It

    **<a href="**">

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

Example 477Try It

    __<a href="__">

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

Example 478Try It

    *a `*`*

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

Example 479Try It

    _a `_`_

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

Example 480Try It

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

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

Example 481Try It

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

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

## 6.3Links

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

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

- Links may not contain other links, at any level of nesting. If multiple otherwise valid link definitions appear nested inside each other, the inner-most definition is used.

- Brackets are allowed in the link text only if (a) they are backslash-escaped or (b) they appear as a matched pair of brackets, with an open bracket `[`, a sequence of zero or more inlines, and a close bracket `]`.

- Backtick code spans, autolinks, and raw HTML tags bind more tightly than the brackets in link text. Thus, for example, `[foo`]`` could not be a link text, since the second `]` is part of a code span.

- The brackets in link text bind more tightly than markers for emphasis and strong emphasis. Thus, for example, `*[foo*](url)` is a link.

A link destination consists of either

- a sequence of zero or more characters between an opening `<` and a closing `>` that contains no line endings or unescaped `<` or `>` characters, or

- a nonempty sequence of characters that does not start with `<`, does not include ASCII control characters or space character, and includes parentheses only if (a) they are backslash-escaped or (b) they are part of a balanced pair of unescaped parentheses. (Implementations may impose limits on parentheses nesting to avoid performance issues, but at least three levels of nesting should be supported.)

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 `(` or `)` character only if it is backslash-escaped.

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

An inline link consists of a link text followed immediately by a left parenthesis `(`, an optional link destination, an optional link title, and a right parenthesis `)`. These four components may be separated by spaces, tabs, and up to one line ending. If both link destination and link title are present, they must be separated by spaces, tabs, and up to one line ending.

The link’s text consists of the inlines contained in the link text (excluding the enclosing square brackets). The link’s URI consists of the link destination, excluding enclosing `<...>` if present, with backslash-escapes in effect as described above. The link’s title consists of the link title, excluding its enclosing delimiters, with backslash-escapes in effect as described above.

Here is a simple inline link:

Example 482Try It

    [link](/uri "title")

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

The title, the link text and even the destination may be omitted:

Example 483Try It

    [link](/uri)

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

Example 484Try It

    [](./target.md)

    <p><a href="./target.md"></a></p>

Example 485Try It

    [link]()

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

Example 486Try It

    [link](<>)

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

Example 487Try It

    []()

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

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

Example 488Try It

    [link](/my uri)

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

Example 489Try It

    [link](</my uri>)

    <p><a href="/my%20uri">link</a></p>

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

Example 490Try It

    [link](foo
    bar)

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

Example 491Try It

    [link](<foo
    bar>)

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

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

Example 492Try It

    [a](<b)c>)

    <p><a href="b)c">a</a></p>

Pointy brackets that enclose links must be unescaped:

Example 493Try It

    [link](<foo\>)

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

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

Example 494Try It

    [a](<b)c
    [a](<b)c>
    [a](<b>c)

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

Parentheses inside the link destination may be escaped:

Example 495Try It

    [link](\(foo\))

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

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

Example 496Try It

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

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

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

Example 497Try It

    [link](foo(and(bar))

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

Example 498Try It

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

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

Example 499Try It

    [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 500Try It

    [link](foo\)\:)

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

A link can contain fragment identifiers and queries:

Example 501Try It

    [link](#fragment)

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

    [link](https://example.com?foo=3#frag)

    <p><a href="#fragment">link</a></p>
    <p><a href="https://example.com#fragment">link</a></p>
    <p><a href="https://example.com?foo=3#frag">link</a></p>

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

Example 502Try It

    [link](foo\bar)

    <p><a href="foo%5Cbar">link</a></p>

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

Example 503Try It

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

    <p><a href="foo%20b%C3%A4">link</a></p>

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

Example 504Try It

    [link]("title")

    <p><a href="%22title%22">link</a></p>

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

Example 505Try It

    [link](/url "title")
    [link](/url 'title')
    [link](/url (title))

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

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

Example 506Try It

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

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

Titles must be separated from the link using spaces, tabs, and up to one line ending. Other Unicode whitespace like non-breaking space doesn’t work.

Example 507Try It

    [link](/url "title")

    <p><a href="/url%C2%A0%22title%22">link</a></p>

Nested balanced quotes are not allowed without escaping:

Example 508Try It

    [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 509Try It

    [link](/url 'title "and" title')

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

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

Spaces, tabs, and up to one line ending is allowed around the destination and title:

Example 510Try It

    [link](   /uri
      "title"  )

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

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

Example 511Try It

    [link] (/uri)

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

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

Example 512Try It

    [link [foo [bar]]](/uri)

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

Example 513Try It

    [link] bar](/uri)

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

Example 514Try It

    [link [bar](/uri)

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

Example 515Try It

    [link \[bar](/uri)

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

The link text may contain inline content:

Example 516Try It

    [link *foo **bar** `#`*](/uri)

    <p><a href="/uri">link <em>foo <strong>bar</strong> <code>#</code></em></a></p>

Example 517Try It

    [![moon](moon.jpg)](/uri)

    <p><a href="/uri"><img src="moon.jpg" alt="moon" /></a></p>

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

Example 518Try It

    [foo [bar](/uri)](/uri)

    <p>[foo <a href="/uri">bar</a>](/uri)</p>

Example 519Try It

    [foo *[bar [baz](/uri)](/uri)*](/uri)

    <p>[foo <em>[bar <a href="/uri">baz</a>](/uri)</em>](/uri)</p>

Example 520Try It

    ![[[foo](uri1)](uri2)](uri3)

    <p><img src="uri3" alt="[foo](uri2)" /></p>

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

Example 521Try It

    *[foo*](/uri)

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

Example 522Try It

    [foo *bar](baz*)

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

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

Example 523Try It

    *foo [bar* baz]

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

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

Example 524Try It

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

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

Example 525Try It

    [foo`](/uri)`

    <p>[foo<code>](/uri)</code></p>

Example 526Try It

    [foo<https://example.com/?search=](uri)>

    <p>[foo<a href="https://example.com/?search=%5D(uri)">https://example.com/?search=](uri)</a></p>

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

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

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

One label matches another just in case their normalized forms are equal. To normalize a label, strip off the opening and closing brackets, perform the Unicode case fold, strip leading and trailing spaces, tabs, and line endings, and collapse consecutive internal spaces, tabs, and line endings 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 link’s URI and title are provided by the matching link reference definition.

Here is a simple example:

Example 527Try It

    [foo][bar]

    [bar]: /url "title"

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

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

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

Example 528Try It

    [link [foo [bar]]][ref]

    [ref]: /uri

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

Example 529Try It

    [link \[bar][ref]

    [ref]: /uri

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

The link text may contain inline content:

Example 530Try It

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

    [ref]: /uri

    <p><a href="/uri">link <em>foo <strong>bar</strong> <code>#</code></em></a></p>

Example 531Try It

    [![moon](moon.jpg)][ref]

    [ref]: /uri

    <p><a href="/uri"><img src="moon.jpg" alt="moon" /></a></p>

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

Example 532Try It

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

    [ref]: /uri

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

Example 533Try It

    [foo *bar [baz][ref]*][ref]

    [ref]: /uri

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

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

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

Example 534Try It

    *[foo*][ref]

    [ref]: /uri

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

Example 535Try It

    [foo *bar][ref]*

    [ref]: /uri

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

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

Example 536Try It

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

    [ref]: /uri

    <p>[foo <bar attr="][ref]"></p>

Example 537Try It

    [foo`][ref]`

    [ref]: /uri

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

Example 538Try It

    [foo<https://example.com/?search=][ref]>

    [ref]: /uri

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

Matching is case-insensitive:

Example 539Try It

    [foo][BaR]

    [bar]: /url "title"

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

Unicode case fold is used:

Example 540Try It

    [ẞ]

    [SS]: /url

    <p><a href="/url">ẞ</a></p>

Consecutive internal spaces, tabs, and line endings are treated as one space for purposes of determining matching:

Example 541Try It

    [Foo
      bar]: /url

    [Baz][Foo bar]

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

No spaces, tabs, or line endings are allowed between the link text and the link label:

Example 542Try It

    [foo] [bar]

    [bar]: /url "title"

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

Example 543Try It

    [foo]
    [bar]

    [bar]: /url "title"

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

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

    [foo]
    [bar]

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

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

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

Example 544Try It

    [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 545Try It

    [bar][foo\!]

    [foo!]: /url

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

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

Example 546Try It

    [foo][ref[]

    [ref[]: /uri

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

Example 547Try It

    [foo][ref[bar]]

    [ref[bar]]: /uri

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

Example 548Try It

    [[[foo]]]

    [[[foo]]]: /url

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

Example 549Try It

    [foo][ref\[]

    [ref\[]: /uri

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

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

Example 550Try It

    [bar\\]: /uri

    [bar\\]

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

A link label must contain at least one character that is not a space, tab, or line ending:

Example 551Try It

    []

    []: /uri

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

Example 552Try It

    [
     ]

    [
     ]: /uri

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

A collapsed reference link consists of a link label that matches a link reference definition elsewhere in the document, followed by the string `[]`. The contents of the 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 553Try It

    [foo][]

    [foo]: /url "title"

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

Example 554Try It

    [*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 555Try It

    [Foo][]

    [foo]: /url "title"

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

As with full reference links, spaces, tabs, or line endings are not allowed between the two sets of brackets:

Example 556Try It

    [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 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 557Try It

    [foo]

    [foo]: /url "title"

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

Example 558Try It

    [*foo* bar]

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

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

Example 559Try It

    [[*foo* bar]]

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

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

Example 560Try It

    [[bar [foo]

    [foo]: /url

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

The link labels are case-insensitive:

Example 561Try It

    [Foo]

    [foo]: /url "title"

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

A space after the link text should be preserved:

Example 562Try It

    [foo] bar

    [foo]: /url

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

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

Example 563Try It

    \[foo]

    [foo]: /url "title"

    <p>[foo]</p>

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

Example 564Try It

    [foo*]: /url

    *[foo*]

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

Full and collapsed references take precedence over shortcut references:

Example 565Try It

    [foo][bar]

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

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

Example 566Try It

    [foo][]

    [foo]: /url1

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

Inline links also take precedence:

Example 567Try It

    [foo]()

    [foo]: /url1

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

Example 568Try It

    [foo](not a link)

    [foo]: /url1

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

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

Example 569Try It

    [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 570Try It

    [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 571Try It

    [foo][bar][baz]

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

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

## 6.4Images

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

Example 572Try It

    ![foo](/url "title")

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

Example 573Try It

    ![foo *bar*]

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

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

Example 574Try It

    ![foo ![bar](/url)](/url2)

    <p><img src="/url2" alt="foo bar" /></p>

Example 575Try It

    ![foo [bar](/url)](/url2)

    <p><img src="/url2" alt="foo bar" /></p>

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

Example 576Try It

    ![foo *bar*][]

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

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

Example 577Try It

    ![foo *bar*][foobar]

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

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

Example 578Try It

    ![foo](train.jpg)

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

Example 579Try It

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

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

Example 580Try It

    ![foo](<url>)

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

Example 581Try It

    ![](/url)

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

Reference-style:

Example 582Try It

    ![foo][bar]

    [bar]: /url

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

Example 583Try It

    ![foo][bar]

    [BAR]: /url

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

Collapsed:

Example 584Try It

    ![foo][]

    [foo]: /url "title"

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

Example 585Try It

    ![*foo* bar][]

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

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

The labels are case-insensitive:

Example 586Try It

    ![Foo][]

    [foo]: /url "title"

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

As with reference links, spaces, tabs, and line endings, are not allowed between the two sets of brackets:

Example 587Try It

    ![foo]
    []

    [foo]: /url "title"

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

Shortcut:

Example 588Try It

    ![foo]

    [foo]: /url "title"

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

Example 589Try It

    ![*foo* bar]

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

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

Note that link labels cannot contain unescaped brackets:

Example 590Try It

    ![[foo]]

    [[foo]]: /url "title"

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

The link labels are case-insensitive:

Example 591Try It

    ![Foo]

    [foo]: /url "title"

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

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

Example 592Try It

    !\[foo]

    [foo]: /url "title"

    <p>![foo]</p>

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

Example 593Try It

    \![foo]

    [foo]: /url "title"

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

## 6.5Autolinks

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

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

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

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

Here are some valid autolinks:

Example 594Try It

    <http://foo.bar.baz>

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

Example 595Try It

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

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

Example 596Try It

    <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 597Try It

    <MAILTO:FOO@BAR.BAZ>

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

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

Example 598Try It

    <a+b+c:d>

    <p><a href="a+b+c:d">a+b+c:d</a></p>

Example 599Try It

    <made-up-scheme://foo,bar>

    <p><a href="made-up-scheme://foo,bar">made-up-scheme://foo,bar</a></p>

Example 600Try It

    <https://../>

    <p><a href="https://../">https://../</a></p>

Example 601Try It

    <localhost:5001/foo>

    <p><a href="localhost:5001/foo">localhost:5001/foo</a></p>

Spaces are not allowed in autolinks:

Example 602Try It

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

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

Backslash-escapes do not work inside autolinks:

Example 603Try It

    <https://example.com/\[\>

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

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

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

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

Examples of email autolinks:

Example 604Try It

    <foo@bar.example.com>

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

Example 605Try It

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

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

Backslash-escapes do not work inside email autolinks:

Example 606Try It

    <foo\+@bar.example.com>

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

These are not autolinks:

Example 607Try It

    <>

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

Example 608Try It

    < https://foo.bar >

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

Example 609Try It

    <m:abc>

    <p>&lt;m:abc&gt;</p>

Example 610Try It

    <foo.bar.baz>

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

Example 611Try It

    https://example.com

    <p>https://example.com</p>

Example 612Try It

    foo@bar.example.com

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

## 6.6Raw HTML

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

Here is the grammar for tags:

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

An attribute consists of spaces, tabs, and up to one line ending, 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 spaces, tabs, and up to one line ending, a `=` character, optional spaces, tabs, and up to one line ending, 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, tabs, line endings, `"`, `'`, `=`, `<`, `>`, 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 spaces, tabs, and up to one line ending, an optional `/` character, and a `>` character.

A closing tag consists of the string `</`, a tag name, optional spaces, tabs, and up to one line ending, and the character `>`.

An HTML comment consists of `<!-->`, `<!--->`, or `<!--`, a string of characters not including the string `-->`, and `-->` (see the HTML spec).

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

A declaration consists of the string `<!`, an ASCII letter, zero or more characters not including the character `>`, and the character `>`.

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

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

Here are some simple open tags:

Example 613Try It

    <a><bab><c2c>

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

Empty elements:

Example 614Try It

    <a/><b2/>

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

Whitespace is allowed:

Example 615Try It

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

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

With attributes:

Example 616Try It

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

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

Custom tag names can be used:

Example 617Try It

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

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

Illegal tag names, not parsed as HTML:

Example 618Try It

    <33> <__>

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

Illegal attribute names:

Example 619Try It

    <a h*#ref="hi">

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

Illegal attribute values:

Example 620Try It

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

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

Illegal whitespace:

Example 621Try It

    < a><
    foo><bar/ >
    <foo bar=baz
    bim!bop />

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

Missing whitespace:

Example 622Try It

    <a href='bar'title=title>

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

Closing tags:

Example 623Try It

    </a></foo >

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

Illegal attributes in closing tag:

Example 624Try It

    </a href="foo">

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

Comments:

Example 625Try It

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

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

Example 626Try It

    foo <!--> foo -->

    foo <!---> foo -->

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

Processing instructions:

Example 627Try It

    foo <?php echo $a; ?>

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

Declarations:

Example 628Try It

    foo <!ELEMENT br EMPTY>

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

CDATA sections:

Example 629Try It

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

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

Entity and numeric character references are preserved in HTML attributes:

Example 630Try It

    foo <a href="&ouml;">

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

Backslash escapes do not work in HTML attributes:

Example 631Try It

    foo <a href="\*">

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

Example 632Try It

    <a href="\"">

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

## 6.7Hard line breaks

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

Example 633Try It

    foo
    baz

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

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

Example 634Try It

    foo\
    baz

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

More than two spaces can be used:

Example 635Try It

    foo
    baz

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

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

Example 636Try It

    foo
         bar

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

Example 637Try It

    foo\
         bar

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

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

Example 638Try It

    *foo
    bar*

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

Example 639Try It

    *foo\
    bar*

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

Hard line breaks do not occur inside code spans

Example 640Try It

    `code
    span`

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

Example 641Try It

    `code\
    span`

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

or HTML tags:

Example 642Try It

    <a href="foo
    bar">

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

Example 643Try It

    <a href="foo\
    bar">

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

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

Example 644Try It

    foo\

    <p>foo\</p>

Example 645Try It

    foo

    <p>foo</p>

Example 646Try It

    ### foo\

    <h3>foo\</h3>

Example 647Try It

    ### foo

    <h3>foo</h3>

## 6.8Soft line breaks

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

Example 648Try It

    foo
    baz

    <p>foo
    baz</p>

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

Example 649Try It

    foo
     baz

    <p>foo
    baz</p>

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

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

## 6.9Textual content

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

Example 650Try It

    hello $.;'there

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

Example 651Try It

    Foo χρῆν

    <p>Foo χρῆν</p>

Internal spaces are preserved verbatim:

Example 652Try It

    Multiple     spaces

    <p>Multiple     spaces</p>

# Appendix: A parsing strategy

In this appendix we describe some features of the parsing strategy used in the CommonMark reference implementations.

## Overview

Parsing has two phases:

1. 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.

2. In the second phase, the raw text contents of paragraphs and headings 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.

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"

## Phase 1: block structure

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:

1. One or more open blocks may be closed.
2. One or more new blocks may be created as children of the last open block.
3. 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.

For each line, we follow this procedure:

1. First we iterate through the open blocks, starting with the root document, and descending through last children down to the last open block. Each block imposes a condition that the line must satisfy if the block is to remain open. For example, a block quote requires a `>` character. A paragraph requires a non-blank line. In this phase we may match all or just some of the open blocks. But we cannot close unmatched blocks yet, because we may have a lazy continuation line.

2. Next, after consuming the continuation markers for existing blocks, we look for new block starts (e.g. `>` for a block quote). If we encounter a new block start, we close any blocks unmatched in step 1 before creating the new block as a child of the last matched container block.

3. Finally, we look at the remainder of the line (after block markers like `>`, list markers, and indentation have been consumed). This is text that can be incorporated into the last open block (a paragraph, code block, heading, or raw HTML).

Setext headings are formed when we see a line of a paragraph that is a setext heading underline.

Reference link definitions are detected when a paragraph is closed; the accumulated text lines are parsed to see if they begin with one or more reference link definitions. Any remainder becomes a normal paragraph.

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"

## Phase 2: inline structure

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 headings 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 line ending in the first paragraph has been parsed as a `softbreak`, and the asterisks in the first list item have become an `emph`.

### An algorithm for parsing nested emphasis and links

By far the trickiest part of inline parsing is handling emphasis, strong emphasis, links, and images. This is done using the following algorithm.

When we’re parsing inlines and we hit either

- a run of `*` or `_` characters, or
- a `[` or `![`

we insert a text node with these symbols as its literal content, and we add a pointer to this text node to the delimiter stack.

The delimiter stack is a doubly linked list. Each element contains a pointer to a text node, plus information about

- the type of delimiter (`[`, `![`, `*`, `_`)
- the number of delimiters,
- whether the delimiter is “active” (all are active to start), and
- whether the delimiter is a potential opener, a potential closer, or both (which depends on what sort of characters precede and follow the delimiters).

When we hit a `]` character, we call the look for link or image procedure (see below).

When we hit the end of the input, we call the process emphasis procedure (see below), with `stack_bottom` = NULL.

#### look for link or image

Starting at the top of the delimiter stack, we look backwards through the stack for an opening `[` or `![` delimiter.

- If we don’t find one, we return a literal text node `]`.

- If we do find one, but it’s not active, we remove the inactive delimiter from the stack, and return a literal text node `]`.

- If we find one and it’s active, then we parse ahead to see if we have an inline link/image, reference link/image, collapsed reference link/image, or shortcut reference link/image.

  - If we don’t, then we remove the opening delimiter from the delimiter stack and return a literal text node `]`.

  - If we do, then

    - We return a link or image node whose children are the inlines after the text node pointed to by the opening delimiter.

    - We run process emphasis on these inlines, with the `[` opener as `stack_bottom`.

    - We remove the opening delimiter.

    - If we have a link (and not an image), we also set all `[` delimiters before the opening delimiter to inactive. (This will prevent us from getting links within links.)

#### process emphasis

Parameter `stack_bottom` sets a lower bound to how far we descend in the delimiter stack. If it is NULL, we can go all the way to the bottom. Otherwise, we stop before visiting `stack_bottom`.

Let `current_position` point to the element on the delimiter stack just above `stack_bottom` (or the first element if `stack_bottom` is NULL).

We keep track of the `openers_bottom` for each delimiter type (`*`, `_`), indexed to the length of the closing delimiter run (modulo 3) and to whether the closing delimiter can also be an opener. Initialize this to `stack_bottom`.

Then we repeat the following until we run out of potential closers:

- Move `current_position` forward in the delimiter stack (if needed) until we find the first potential closer with delimiter `*` or `_`. (This will be the potential closer closest to the beginning of the input – the first one in parse order.)

- Now, look back in the stack (staying above `stack_bottom` and the `openers_bottom` for this delimiter type) for the first matching potential opener (“matching” means same delimiter).

- If one is found:

  - Figure out whether we have emphasis or strong emphasis: if both closer and opener spans have length >= 2, we have strong, otherwise regular.

  - Insert an emph or strong emph node accordingly, after the text node corresponding to the opener.

  - Remove any delimiters between the opener and closer from the delimiter stack.

  - Remove 1 (for regular emph) or 2 (for strong emph) delimiters from the opening and closing text nodes. If they become empty as a result, remove them and remove the corresponding element of the delimiter stack. If the closing node is removed, reset `current_position` to the next element in the stack.

- If none is found:

  - Set `openers_bottom` to the element before `current_position`. (We know that there are no openers for this kind of closer up to and including this point, so this puts a lower bound on future searches.)

  - If the closer at `current_position` is not a potential opener, remove it from the delimiter stack (since we know it can’t be a closer either).

  - Advance `current_position` to the next element in the stack.

After we’re done, we remove all delimiters above `stack_bottom` from the delimiter stack.