Couldn't find wdiff. Falling back to builtin diff colouring... Diff: spec.txt - spec.txt
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--- ---
title: CommonMark Spec title: CommonMark Spec
author: John MacFarlane author: John MacFarlane
version: 0.27 version: 0.28
date: '2016-11-18' date: '2017-08-01'
license: '[CC-BY-SA 4.0](http://creativecommons.org/licenses/by-sa/4.0/)' license: '[CC-BY-SA 4.0](http://creativecommons.org/licenses/by-sa/4.0/)'
... ...
# Introduction # Introduction
## What is Markdown? ## What is Markdown?
Markdown is a plain text format for writing structured documents, Markdown is a plain text format for writing structured documents,
based on conventions used for indicating formatting in email and based on conventions for indicating formatting in email
usenet posts. It was developed in 2004 by John Gruber, who wrote and usenet posts. It was developed by John Gruber (with
the first Markdown-to-HTML converter in Perl, and it soon became help from Aaron Swartz) and released in 2004 in the form of a
ubiquitous. In the next decade, dozens of implementations were [syntax description](http://daringfireball.net/projects/markdown/syntax)
and a Perl script (`Markdown.pl`) for converting Markdown to
HTML. In the next decade, dozens of implementations were
developed in many languages. Some extended the original developed in many languages. Some extended the original
Markdown syntax with conventions for footnotes, tables, and Markdown syntax with conventions for footnotes, tables, and
other document elements. Some allowed Markdown documents to be other document elements. Some allowed Markdown documents to be
rendered in formats other than HTML. Websites like Reddit, rendered in formats other than HTML. Websites like Reddit,
StackOverflow, and GitHub had millions of people using Markdown. StackOverflow, and GitHub had millions of people using Markdown.
And Markdown started to be used beyond the web, to author books, And Markdown started to be used beyond the web, to author books,
articles, slide shows, letters, and lecture notes. articles, slide shows, letters, and lecture notes.
What distinguishes Markdown from many other lightweight markup What distinguishes Markdown from many other lightweight markup
syntaxes, which are often easier to write, is its readability. syntaxes, which are often easier to write, is its readability.
skipping to change at line 315 skipping to change at line 317
The following definitions of character classes will be used in this spec: The following definitions of character classes will be used in this spec:
A [whitespace character](@) is a space A [whitespace character](@) is a space
(`U+0020`), tab (`U+0009`), newline (`U+000A`), line tabulation (`U+000B`), (`U+0020`), tab (`U+0009`), newline (`U+000A`), line tabulation (`U+000B`),
form feed (`U+000C`), or carriage return (`U+000D`). form feed (`U+000C`), or carriage return (`U+000D`).
[Whitespace](@) is a sequence of one or more [whitespace [Whitespace](@) is a sequence of one or more [whitespace
characters]. characters].
A [Unicode whitespace character](@) is A [Unicode whitespace character](@) is
any code point in the Unicode `Zs` class, or a tab (`U+0009`), any code point in the Unicode `Zs` general category, or a tab (`U+0009`),
carriage return (`U+000D`), newline (`U+000A`), or form feed carriage return (`U+000D`), newline (`U+000A`), or form feed
(`U+000C`). (`U+000C`).
[Unicode whitespace](@) is a sequence of one [Unicode whitespace](@) is a sequence of one
or more [Unicode whitespace characters]. or more [Unicode whitespace characters].
A [space](@) is `U+0020`. A [space](@) is `U+0020`.
A [non-whitespace character](@) is any character A [non-whitespace character](@) is any character
that is not a [whitespace character]. that is not a [whitespace character].
An [ASCII punctuation character](@) An [ASCII punctuation character](@)
is `!`, `"`, `#`, `$`, `%`, `&`, `'`, `(`, `)`, is `!`, `"`, `#`, `$`, `%`, `&`, `'`, `(`, `)`,
`*`, `+`, `,`, `-`, `.`, `/`, `:`, `;`, `<`, `=`, `>`, `?`, `@`, `*`, `+`, `,`, `-`, `.`, `/`, `:`, `;`, `<`, `=`, `>`, `?`, `@`,
`[`, `\`, `]`, `^`, `_`, `` ` ``, `{`, `|`, `}`, or `~`. `[`, `\`, `]`, `^`, `_`, `` ` ``, `{`, `|`, `}`, or `~`.
A [punctuation character](@) is an [ASCII A [punctuation character](@) is an [ASCII
punctuation character] or anything in punctuation character] or anything in
the Unicode classes `Pc`, `Pd`, `Pe`, `Pf`, `Pi`, `Po`, or `Ps`. the general Unicode categories `Pc`, `Pd`, `Pe`, `Pf`, `Pi`, `Po`, or `Ps`.
## Tabs ## Tabs
Tabs in lines are not expanded to [spaces]. However, Tabs in lines are not expanded to [spaces]. However,
in contexts where whitespace helps to define block structure, in contexts where whitespace helps to define block structure,
tabs behave as if they were replaced by spaces with a tab stop tabs behave as if they were replaced by spaces with a tab stop
of 4 characters. of 4 characters.
Thus, for example, a tab can be used instead of four spaces Thus, for example, a tab can be used instead of four spaces
in an indented code block. (Note, however, that internal in an indented code block. (Note, however, that internal
skipping to change at line 405 skipping to change at line 407
<p>foo</p> <p>foo</p>
<pre><code> bar <pre><code> bar
</code></pre> </code></pre>
</li> </li>
</ul> </ul>
```````````````````````````````` ````````````````````````````````
Normally the `>` that begins a block quote may be followed Normally the `>` that begins a block quote may be followed
optionally by a space, which is not considered part of the optionally by a space, which is not considered part of the
content. In the following case `>` is followed by a tab, content. In the following case `>` is followed by a tab,
which is treated as if it were expanded into spaces. which is treated as if it were expanded into three spaces.
Since one of theses spaces is considered part of the Since one of these spaces is considered part of the
delimiter, `foo` is considered to be indented six spaces delimiter, `foo` is considered to be indented six spaces
inside the block quote context, so we get an indented inside the block quote context, so we get an indented
code block starting with two spaces. code block starting with two spaces.
```````````````````````````````` example ```````````````````````````````` example
>→→foo >→→foo
. .
<blockquote> <blockquote>
<pre><code> foo <pre><code> foo
</code></pre> </code></pre>
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For security reasons, the Unicode character `U+0000` must be replaced For security reasons, the Unicode character `U+0000` must be replaced
with the REPLACEMENT CHARACTER (`U+FFFD`). with the REPLACEMENT CHARACTER (`U+FFFD`).
# Blocks and inlines # Blocks and inlines
We can think of a document as a sequence of We can think of a document as a sequence of
[blocks](@)---structural elements like paragraphs, block [blocks](@)---structural elements like paragraphs, block
quotations, lists, headings, rules, and code blocks. Some blocks (like quotations, lists, headings, rules, and code blocks. Some blocks (like
block quotes and list items) contain other blocks; others (like block quotes and list items) contain other blocks; others (like
headings and paragraphs) contain [inline](@) content---text, headings and paragraphs) contain [inline](@) content---text,
links, emphasized text, images, code, and so on. links, emphasized text, images, code spans, and so on.
## Precedence ## Precedence
Indicators of block structure always take precedence over indicators Indicators of block structure always take precedence over indicators
of inline structure. So, for example, the following is a list with of inline structure. So, for example, the following is a list with
two items, not a list with one item containing a code span: two items, not a list with one item containing a code span:
```````````````````````````````` example ```````````````````````````````` example
- `one - `one
- two` - two`
skipping to change at line 1559 skipping to change at line 1561
~~~ ~~~
< <
> >
~~~ ~~~
. .
<pre><code>&lt; <pre><code>&lt;
&gt; &gt;
</code></pre> </code></pre>
```````````````````````````````` ````````````````````````````````
Fewer than three backticks is not enough:
```````````````````````````````` example
``
foo
``
.
<p><code>foo</code></p>
````````````````````````````````
The closing code fence must use the same character as the opening The closing code fence must use the same character as the opening
fence: fence:
```````````````````````````````` example ```````````````````````````````` example
``` ```
aaa aaa
~~~ ~~~
``` ```
. .
<pre><code>aaa <pre><code>aaa
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by [whitespace], the end of the line, the string `>`, or by [whitespace], the end of the line, the string `>`, or
the string `/>`.\ the string `/>`.\
**End condition:** line is followed by a [blank line]. **End condition:** line is followed by a [blank line].
7. **Start condition:** line begins with a complete [open tag] 7. **Start condition:** line begins with a complete [open tag]
or [closing tag] (with any [tag name] other than `script`, or [closing tag] (with any [tag name] other than `script`,
`style`, or `pre`) followed only by [whitespace] `style`, or `pre`) followed only by [whitespace]
or the end of the line.\ or the end of the line.\
**End condition:** line is followed by a [blank line]. **End condition:** line is followed by a [blank line].
HTML blocks continue until they are closed by their appropriate
[end condition], or the last line of the document or other [container block].
This means any HTML **within an HTML block** that might otherwise be recognised
as a start condition will be ignored by the parser and passed through as-is,
without changing the parser's state.
For instance, `<pre>` within a HTML block started by `<table>` will not affect
the parser state; as the HTML block was started in by start condition 6, it
will end at any blank line. This can be surprising:
```````````````````````````````` example
<table><tr><td>
<pre>
**Hello**,
_world_.
</pre>
</td></tr></table>
.
<table><tr><td>
<pre>
**Hello**,
<p><em>world</em>.
</pre></p>
</td></tr></table>
````````````````````````````````
In this case, the HTML block is terminated by the newline — the `**hello**`
text remains verbatim — and regular parsing resumes, with a paragraph,
emphasised `world` and inline and block HTML following.
All types of [HTML blocks] except type 7 may interrupt All types of [HTML blocks] except type 7 may interrupt
a paragraph. Blocks of type 7 may not interrupt a paragraph. a paragraph. Blocks of type 7 may not interrupt a paragraph.
(This restriction is intended to prevent unwanted interpretation (This restriction is intended to prevent unwanted interpretation
of long tags inside a wrapped paragraph as starting HTML blocks.) of long tags inside a wrapped paragraph as starting HTML blocks.)
Some simple examples follow. Here are some basic HTML blocks Some simple examples follow. Here are some basic HTML blocks
of type 6: of type 6:
```````````````````````````````` example ```````````````````````````````` example
<table> <table>
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blocks *Bs* starting with a [non-whitespace character] and not separated blocks *Bs* starting with a [non-whitespace character] and not separated
from each other by more than one blank line, and *M* is a list from each other by more than one blank line, and *M* is a list
marker of width *W* followed by 1 ≤ *N* ≤ 4 spaces, then the result marker of width *W* followed by 1 ≤ *N* ≤ 4 spaces, then the result
of prepending *M* and the following spaces to the first line of 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 *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 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. (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 If the list item is ordered, then it is also assigned a start
number, based on the ordered list marker. number, based on the ordered list marker.
Exceptions: When the first list item in a [list] interrupts Exceptions:
a paragraph---that is, when it starts on a line that would
otherwise count as [paragraph continuation text]---then (a) 1. When the first list item in a [list] interrupts
the lines *Ls* must not begin with a blank line, and (b) if a paragraph---that is, when it starts on a line that would
the list item is ordered, the start number must be 1. otherwise count as [paragraph continuation text]---then (a)
the lines *Ls* must not begin with a blank line, and (b) if
the list item is ordered, the start number must be 1.
2. If any line is a [thematic break][thematic breaks] then
that line is not a list item.
For example, let *Ls* be the lines For example, let *Ls* be the lines
```````````````````````````````` example ```````````````````````````````` example
A paragraph A paragraph
with two lines. with two lines.
indented code indented code
> A block quote. > A block quote.
skipping to change at line 5458 skipping to change at line 5505
. .
<p>```foo``</p> <p>```foo``</p>
```````````````````````````````` ````````````````````````````````
```````````````````````````````` example ```````````````````````````````` example
`foo `foo
. .
<p>`foo</p> <p>`foo</p>
```````````````````````````````` ````````````````````````````````
The following case also illustrates the need for opening and
closing backtick strings to be equal in length:
```````````````````````````````` example
`foo``bar``
.
<p>`foo<code>bar</code></p>
````````````````````````````````
## Emphasis and strong emphasis ## Emphasis and strong emphasis
John Gruber's original [Markdown syntax John Gruber's original [Markdown syntax
description](http://daringfireball.net/projects/markdown/syntax#em) says: description](http://daringfireball.net/projects/markdown/syntax#em) says:
> Markdown treats asterisks (`*`) and underscores (`_`) as indicators of > Markdown treats asterisks (`*`) and underscores (`_`) as indicators of
> emphasis. Text wrapped with one `*` or `_` will be wrapped with an HTML > 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>` > `<em>` tag; double `*`'s or `_`'s will be wrapped with an HTML `<strong>`
> tag. > tag.
skipping to change at line 5506 skipping to change at line 5562
``` markdown ``` markdown
internal emphasis: foo*bar*baz internal emphasis: foo*bar*baz
no emphasis: foo_bar_baz no emphasis: foo_bar_baz
``` ```
The rules given below capture all of these patterns, while allowing The rules given below capture all of these patterns, while allowing
for efficient parsing strategies that do not backtrack. for efficient parsing strategies that do not backtrack.
First, some definitions. A [delimiter run](@) is either First, some definitions. A [delimiter run](@) is either
a sequence of one or more `*` characters that is not preceded or a sequence of one or more `*` characters that is not preceded or
followed by a `*` character, or a sequence of one or more `_` followed by a non-backslash-escaped `*` character, or a sequence
characters that is not preceded or followed by a `_` character. of one or more `_` characters that is not preceded or followed by
a non-backslash-escaped `_` character.
A [left-flanking delimiter run](@) is A [left-flanking delimiter run](@) is
a [delimiter run] that is (a) not followed by [Unicode whitespace], a [delimiter run] that is (a) not followed by [Unicode whitespace],
and (b) either not followed by a [punctuation character], or and (b) not followed by a [punctuation character], or
preceded by [Unicode whitespace] or a [punctuation character]. preceded by [Unicode whitespace] or a [punctuation character].
For purposes of this definition, the beginning and the end of For purposes of this definition, the beginning and the end of
the line count as Unicode whitespace. the line count as Unicode whitespace.
A [right-flanking delimiter run](@) is A [right-flanking delimiter run](@) is
a [delimiter run] that is (a) not preceded by [Unicode whitespace], a [delimiter run] that is (a) not preceded by [Unicode whitespace],
and (b) either not preceded by a [punctuation character], or and (b) not preceded by a [punctuation character], or
followed by [Unicode whitespace] or a [punctuation character]. followed by [Unicode whitespace] or a [punctuation character].
For purposes of this definition, the beginning and the end of For purposes of this definition, the beginning and the end of
the line count as Unicode whitespace. the line count as Unicode whitespace.
Here are some examples of delimiter runs. Here are some examples of delimiter runs.
- left-flanking but not right-flanking: - left-flanking but not right-flanking:
``` ```
***abc ***abc
skipping to change at line 5597 skipping to change at line 5654
6. A double `__` [can open strong emphasis] iff 6. A double `__` [can open strong emphasis] iff
it is part of a [left-flanking delimiter run] it is part of a [left-flanking delimiter run]
and either (a) not part of a [right-flanking delimiter run] and either (a) not part of a [right-flanking delimiter run]
or (b) part of a [right-flanking delimiter run] or (b) part of a [right-flanking delimiter run]
preceded by punctuation. preceded by punctuation.
7. A double `**` [can close strong emphasis](@) 7. A double `**` [can close strong emphasis](@)
iff it is part of a [right-flanking delimiter run]. iff it is part of a [right-flanking delimiter run].
8. A double `__` [can close strong emphasis] 8. A double `__` [can close strong emphasis] iff
it is part of a [right-flanking delimiter run] it is part of a [right-flanking delimiter run]
and either (a) not part of a [left-flanking delimiter run] and either (a) not part of a [left-flanking delimiter run]
or (b) part of a [left-flanking delimiter run] or (b) part of a [left-flanking delimiter run]
followed by punctuation. followed by punctuation.
9. Emphasis begins with a delimiter that [can open emphasis] and ends 9. Emphasis begins with a delimiter that [can open emphasis] and ends
with a delimiter that [can close emphasis], and that uses the same with a delimiter that [can close emphasis], and that uses the same
character (`_` or `*`) as the opening delimiter. The character (`_` or `*`) as the opening delimiter. The
opening and closing delimiters must belong to separate opening and closing delimiters must belong to separate
[delimiter runs]. If one of the delimiters can both [delimiter runs]. If one of the delimiters can both
skipping to change at line 5637 skipping to change at line 5694
`_`-delimited emphasis or `__`-delimited strong emphasis, unless it `_`-delimited emphasis or `__`-delimited strong emphasis, unless it
is backslash-escaped. is backslash-escaped.
Where rules 1--12 above are compatible with multiple parsings, Where rules 1--12 above are compatible with multiple parsings,
the following principles resolve ambiguity: the following principles resolve ambiguity:
13. The number of nestings should be minimized. Thus, for example, 13. The number of nestings should be minimized. Thus, for example,
an interpretation `<strong>...</strong>` is always preferred to an interpretation `<strong>...</strong>` is always preferred to
`<em><em>...</em></em>`. `<em><em>...</em></em>`.
14. An interpretation `<strong><em>...</em></strong>` is always 14. An interpretation `<em><strong>...</strong></em>` is always
preferred to `<em><strong>..</strong></em>`. preferred to `<strong><em>...</em></strong>`.
15. When two potential emphasis or strong emphasis spans overlap, 15. When two potential emphasis or strong emphasis spans overlap,
so that the second begins before the first ends and ends after so that the second begins before the first ends and ends after
the first ends, the first takes precedence. Thus, for example, the first ends, the first takes precedence. Thus, for example,
`*foo _bar* baz_` is parsed as `<em>foo _bar</em> baz_` rather `*foo _bar* baz_` is parsed as `<em>foo _bar</em> baz_` rather
than `*foo <em>bar* baz</em>`. than `*foo <em>bar* baz</em>`.
16. When there are two potential emphasis or strong emphasis spans 16. When there are two potential emphasis or strong emphasis spans
with the same closing delimiter, the shorter one (the one that with the same closing delimiter, the shorter one (the one that
opens later) takes precedence. Thus, for example, opens later) takes precedence. Thus, for example,
skipping to change at line 6542 skipping to change at line 6599
******foo****** ******foo******
. .
<p><strong><strong><strong>foo</strong></strong></strong></p> <p><strong><strong><strong>foo</strong></strong></strong></p>
```````````````````````````````` ````````````````````````````````
Rule 14: Rule 14:
```````````````````````````````` example ```````````````````````````````` example
***foo*** ***foo***
. .
<p><strong><em>foo</em></strong></p> <p><em><strong>foo</strong></em></p>
```````````````````````````````` ````````````````````````````````
```````````````````````````````` example ```````````````````````````````` example
_____foo_____ _____foo_____
. .
<p><strong><strong><em>foo</em></strong></strong></p> <p><em><strong><strong>foo</strong></strong></em></p>
```````````````````````````````` ````````````````````````````````
Rule 15: Rule 15:
```````````````````````````````` example ```````````````````````````````` example
*foo _bar* baz_ *foo _bar* baz_
. .
<p><em>foo _bar</em> baz_</p> <p><em>foo _bar</em> baz_</p>
```````````````````````````````` ````````````````````````````````
skipping to change at line 6674 skipping to change at line 6731
A [link destination](@) consists of either A [link destination](@) consists of either
- a sequence of zero or more characters between an opening `<` and a - a sequence of zero or more characters between an opening `<` and a
closing `>` that contains no spaces, line breaks, or unescaped closing `>` that contains no spaces, line breaks, or unescaped
`<` or `>` characters, or `<` or `>` characters, or
- a nonempty sequence of characters that does not include - a nonempty sequence of characters that does not include
ASCII space or control characters, and includes parentheses ASCII space or control characters, and includes parentheses
only if (a) they are backslash-escaped or (b) they are part of only if (a) they are backslash-escaped or (b) they are part of
a balanced pair of unescaped parentheses that is not itself a balanced pair of unescaped parentheses. (Implementations
inside a balanced pair of unescaped parentheses. 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 [link title](@) consists of either
- a sequence of zero or more characters between straight double-quote - a sequence of zero or more characters between straight double-quote
characters (`"`), including a `"` character only if it is characters (`"`), including a `"` character only if it is
backslash-escaped, or backslash-escaped, or
- a sequence of zero or more characters between straight single-quote - a sequence of zero or more characters between straight single-quote
characters (`'`), including a `'` character only if it is characters (`'`), including a `'` character only if it is
backslash-escaped, or backslash-escaped, or
skipping to change at line 6774 skipping to change at line 6832
```````````````````````````````` ````````````````````````````````
Parentheses inside the link destination may be escaped: Parentheses inside the link destination may be escaped:
```````````````````````````````` example ```````````````````````````````` example
[link](\(foo\)) [link](\(foo\))
. .
<p><a href="(foo)">link</a></p> <p><a href="(foo)">link</a></p>
```````````````````````````````` ````````````````````````````````
One level of balanced parentheses is allowed without escaping: Any number of parentheses are allowed without escaping, as long as they are
balanced:
```````````````````````````````` example
[link]((foo)and(bar))
.
<p><a href="(foo)and(bar)">link</a></p>
````````````````````````````````
However, if you have parentheses within parentheses, you need to escape
or use the `<...>` form:
```````````````````````````````` example ```````````````````````````````` example
[link](foo(and(bar))) [link](foo(and(bar)))
. .
<p>[link](foo(and(bar)))</p> <p><a href="foo(and(bar))">link</a></p>
```````````````````````````````` ````````````````````````````````
However, if you have unbalanced parentheses, you need to escape or use the
`<...>` form:
```````````````````````````````` example ```````````````````````````````` example
[link](foo(and\(bar\))) [link](foo\(and\(bar\))
. .
<p><a href="foo(and(bar))">link</a></p> <p><a href="foo(and(bar)">link</a></p>
```````````````````````````````` ````````````````````````````````
```````````````````````````````` example ```````````````````````````````` example
[link](<foo(and(bar))>) [link](<foo(and(bar)>)
. .
<p><a href="foo(and(bar))">link</a></p> <p><a href="foo(and(bar)">link</a></p>
```````````````````````````````` ````````````````````````````````
Parentheses and other symbols can also be escaped, as usual Parentheses and other symbols can also be escaped, as usual
in Markdown: in Markdown:
```````````````````````````````` example ```````````````````````````````` example
[link](foo\)\:) [link](foo\)\:)
. .
<p><a href="foo):">link</a></p> <p><a href="foo):">link</a></p>
```````````````````````````````` ````````````````````````````````
skipping to change at line 7056 skipping to change at line 7109
[full](#full-reference-link), [collapsed](#collapsed-reference-link), [full](#full-reference-link), [collapsed](#collapsed-reference-link),
and [shortcut](#shortcut-reference-link). and [shortcut](#shortcut-reference-link).
A [full reference link](@) A [full reference link](@)
consists of a [link text] immediately followed by a [link label] consists of a [link text] immediately followed by a [link label]
that [matches] a [link reference definition] elsewhere in the document. that [matches] a [link reference definition] elsewhere in the document.
A [link label](@) begins with a left bracket (`[`) and ends A [link label](@) begins with a left bracket (`[`) and ends
with the first right bracket (`]`) that is not backslash-escaped. with the first right bracket (`]`) that is not backslash-escaped.
Between these brackets there must be at least one [non-whitespace character]. Between these brackets there must be at least one [non-whitespace character].
Unescaped square bracket characters are not allowed in Unescaped square bracket characters are not allowed inside the
[link labels]. A link label can have at most 999 opening and closing square brackets of [link labels]. A link
characters inside the square brackets. label can have at most 999 characters inside the square
brackets.
One label [matches](@) One label [matches](@)
another just in case their normalized forms are equal. To normalize a another just in case their normalized forms are equal. To normalize a
label, perform the *Unicode case fold* and collapse consecutive internal label, strip off the opening and closing brackets,
perform the *Unicode case fold*, strip leading and trailing
[whitespace] and collapse consecutive internal
[whitespace] to a single space. If there are multiple [whitespace] to a single space. If there are multiple
matching reference link definitions, the one that comes first in the matching reference link definitions, the one that comes first in the
document is used. (It is desirable in such cases to emit a warning.) document is used. (It is desirable in such cases to emit a warning.)
The contents of the first link label are parsed as inlines, which are The contents of the first link label are parsed as inlines, which are
used as the link's text. The link's URI and title are provided by the used as the link's text. The link's URI and title are provided by the
matching [link reference definition]. matching [link reference definition].
Here is a simple example: Here is a simple example:
skipping to change at line 7752 skipping to change at line 7808
The link labels are case-insensitive: The link labels are case-insensitive:
```````````````````````````````` example ```````````````````````````````` example
![Foo] ![Foo]
[foo]: /url "title" [foo]: /url "title"
. .
<p><img src="/url" alt="Foo" title="title" /></p> <p><img src="/url" alt="Foo" title="title" /></p>
```````````````````````````````` ````````````````````````````````
If you just want bracketed text, you can backslash-escape the If you just want a literal `!` followed by bracketed text, you can
opening `!` and `[`: backslash-escape the opening `[`:
```````````````````````````````` example ```````````````````````````````` example
\!\[foo] !\[foo]
[foo]: /url "title" [foo]: /url "title"
. .
<p>![foo]</p> <p>![foo]</p>
```````````````````````````````` ````````````````````````````````
If you want a link after a literal `!`, backslash-escape the If you want a link after a literal `!`, backslash-escape the
`!`: `!`:
```````````````````````````````` example ```````````````````````````````` example
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