From 1caeda5b537c5cd30f4fc2bf078a00265473894c Mon Sep 17 00:00:00 2001 From: John MacFarlane Date: Sat, 24 Jan 2015 21:13:50 -0800 Subject: Moved spec.txt to test/ directory. --- test/spec.txt | 7321 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 7321 insertions(+) create mode 100644 test/spec.txt (limited to 'test/spec.txt') diff --git a/test/spec.txt b/test/spec.txt new file mode 100644 index 0000000..e754810 --- /dev/null +++ b/test/spec.txt @@ -0,0 +1,7321 @@ +--- +title: CommonMark Spec +author: John MacFarlane +version: 0.17 +date: 2015-01-24 +license: '[CC-BY-SA 4.0](http://creativecommons.org/licenses/by-sa/4.0/)' +... + +# Introduction + +## What is Markdown? + +Markdown is a plain text format for writing structured documents, +based on conventions used for indicating formatting in email and +usenet posts. It was developed in 2004 by John Gruber, who wrote +the first Markdown-to-HTML converter in perl, and it soon became +widely used in websites. By 2014 there were dozens of +implementations in many languages. Some of them extended basic +Markdown syntax with conventions for footnotes, definition lists, +tables, and other constructs, and some allowed output not just in +HTML but in LaTeX and many other formats. + +## Why is a spec needed? + +John Gruber's [canonical description of Markdown's +syntax](http://daringfireball.net/projects/markdown/syntax) +does not specify the syntax unambiguously. Here are some examples of +questions it does not answer: + +1. How much indentation is needed for a sublist? The spec says that + continuation paragraphs need to be indented four spaces, but is + not fully explicit about sublists. It is natural to think that + they, too, must be indented four spaces, but `Markdown.pl` does + not require that. This is hardly a "corner case," and divergences + between implementations on this issue often lead to surprises for + users in real documents. (See [this comment by John + Gruber](http://article.gmane.org/gmane.text.markdown.general/1997).) + +2. Is a blank line needed before a block quote or header? + Most implementations do not require the blank line. However, + this can lead to unexpected results in hard-wrapped text, and + also to ambiguities in parsing (note that some implementations + put the header inside the blockquote, while others do not). + (John Gruber has also spoken [in favor of requiring the blank + lines](http://article.gmane.org/gmane.text.markdown.general/2146).) + +3. Is a blank line needed before an indented code block? + (`Markdown.pl` requires it, but this is not mentioned in the + documentation, and some implementations do not require it.) + + ``` markdown + paragraph + code? + ``` + +4. What is the exact rule for determining when list items get + wrapped in `

` tags? Can a list be partially "loose" and partially + "tight"? What should we do with a list like this? + + ``` markdown + 1. one + + 2. two + 3. three + ``` + + Or this? + + ``` markdown + 1. one + - a + + - b + 2. two + ``` + + (There are some relevant comments by John Gruber + [here](http://article.gmane.org/gmane.text.markdown.general/2554).) + +5. Can list markers be indented? Can ordered list markers be right-aligned? + + ``` markdown + 8. item 1 + 9. item 2 + 10. item 2a + ``` + +6. Is this one list with a horizontal rule in its second item, + or two lists separated by a horizontal rule? + + ``` markdown + * a + * * * * * + * b + ``` + +7. When list markers change from numbers to bullets, do we have + two lists or one? (The Markdown syntax description suggests two, + but the perl scripts and many other implementations produce one.) + + ``` markdown + 1. fee + 2. fie + - foe + - fum + ``` + +8. What are the precedence rules for the markers of inline structure? + For example, is the following a valid link, or does the code span + take precedence ? + + ``` markdown + [a backtick (`)](/url) and [another backtick (`)](/url). + ``` + +9. What are the precedence rules for markers of emphasis and strong + emphasis? For example, how should the following be parsed? + + ``` markdown + *foo *bar* baz* + ``` + +10. What are the precedence rules between block-level and inline-level + structure? For example, how should the following be parsed? + + ``` markdown + - `a long code span can contain a hyphen like this + - and it can screw things up` + ``` + +11. Can list items include section headers? (`Markdown.pl` does not + allow this, but does allow blockquotes to include headers.) + + ``` markdown + - # Heading + ``` + +12. Can list items be empty? + + ``` markdown + * a + * + * b + ``` + +13. Can link references be defined inside block quotes or list items? + + ``` markdown + > Blockquote [foo]. + > + > [foo]: /url + ``` + +14. If there are multiple definitions for the same reference, which takes + precedence? + + ``` markdown + [foo]: /url1 + [foo]: /url2 + + [foo][] + ``` + +In the absence of a spec, early implementers consulted `Markdown.pl` +to resolve these ambiguities. But `Markdown.pl` was quite buggy, and +gave manifestly bad results in many cases, so it was not a +satisfactory replacement for a spec. + +Because there is no unambiguous spec, implementations have diverged +considerably. As a result, users are often surprised to find that +a document that renders one way on one system (say, a github wiki) +renders differently on another (say, converting to docbook using +pandoc). To make matters worse, because nothing in Markdown counts +as a "syntax error," the divergence often isn't discovered right away. + +## About this document + +This document attempts to specify Markdown syntax unambiguously. +It contains many examples with side-by-side Markdown and +HTML. These are intended to double as conformance tests. An +accompanying script `spec_tests.py` can be used to run the tests +against any Markdown program: + + python test/spec_tests.py --spec spec.txt --program PROGRAM + +Since this document describes how Markdown is to be parsed into +an abstract syntax tree, it would have made sense to use an abstract +representation of the syntax tree instead of HTML. But HTML is capable +of representing the structural distinctions we need to make, and the +choice of HTML for the tests makes it possible to run the tests against +an implementation without writing an abstract syntax tree renderer. + +This document is generated from a text file, `spec.txt`, written +in Markdown with a small extension for the side-by-side tests. +The script `spec2md.pl` can be used to turn `spec.txt` into pandoc +Markdown, which can then be converted into other formats. + +In the examples, the `→` character is used to represent tabs. + +# Preliminaries + +## Characters and lines + +Any sequence of [character]s is a valid CommonMark +document. + +A [character](@character) is a unicode code point. +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](@line) is a sequence of zero or more [character]s +followed by a [line ending] or by the end of file. + +A [line ending](@line-ending) is, depending on the platform, a +newline (`U+000A`), carriage return (`U+000D`), or +carriage return + newline. + +For security reasons, a conforming parser must strip or replace the +Unicode character `U+0000`. + +A line containing no characters, or a line containing only spaces +(`U+0020`) or tabs (`U+0009`), is called a [blank line](@blank-line). + +The following definitions of character classes will be used in this spec: + +A [whitespace character](@whitespace-character) is a space +(`U+0020`), tab (`U+0009`), carriage return (`U+000D`), or +newline (`U+000A`). + +[Whitespace](@whitespace) is a sequence of one or more [whitespace +character]s. + +A [unicode whitespace character](@unicode-whitespace-character) is +any code point in the unicode `Zs` class, or a tab (`U+0009`), +carriage return (`U+000D`), newline (`U+000A`), or form feed +(`U+000C`). + +[Unicode whitespace](@unicode-whitespace) is a sequence of one +or more [unicode whitespace character]s. + +A [non-space character](@non-space-character) is anything but `U+0020`. + +An [ASCII punctuation character](@ascii-punctuation-character) +is `!`, `"`, `#`, `$`, `%`, `&`, `'`, `(`, `)`, +`*`, `+`, `,`, `-`, `.`, `/`, `:`, `;`, `<`, `=`, `>`, `?`, `@`, +`[`, `\`, `]`, `^`, `_`, `` ` ``, `{`, `|`, `}`, or `~`. + +A [punctuation character](@punctuation-character) is an [ASCII +punctuation character] or anything in +the unicode classes `Pc`, `Pd`, `Pe`, `Pf`, `Pi`, `Po`, or `Ps`. + +## Tab expansion + +Tabs in lines are expanded to spaces, with a tab stop of 4 characters: + +. +→foo→baz→→bim +. +

foo baz     bim
+
+. + +. + a→a + ὐ→a +. +
a   a
+ὐ   a
+
+. + +# Blocks and inlines + +We can think of a document as a sequence of +[blocks](@block)---structural +elements like paragraphs, block quotations, +lists, headers, rules, and code blocks. Blocks can contain other +blocks, or they can contain [inline](@inline) content: +words, spaces, links, emphasized text, images, and inline code. + +## Precedence + +Indicators of block structure always take precedence over indicators +of inline structure. So, for example, the following is a list with +two items, not a list with one item containing a code span: + +. +- `one +- two` +. + +. + +This means that parsing can proceed in two steps: first, the block +structure of the document can be discerned; second, text lines inside +paragraphs, headers, and other block constructs can be parsed for inline +structure. The second step requires information about link reference +definitions that will be available only at the end of the first +step. Note that the first step requires processing lines in sequence, +but the second can be parallelized, since the inline parsing of +one block element does not affect the inline parsing of any other. + +## Container blocks and leaf blocks + +We can divide blocks into two types: +[container block](@container-block)s, +which can contain other blocks, and [leaf block](@leaf-block)s, +which cannot. + +# Leaf blocks + +This section describes the different kinds of leaf block that make up a +Markdown document. + +## Horizontal rules + +A line consisting of 0-3 spaces of indentation, followed by a sequence +of three or more matching `-`, `_`, or `*` characters, each followed +optionally by any number of spaces, forms a +[horizontal rule](@horizontal-rule). + +. +*** +--- +___ +. +
+
+
+. + +Wrong characters: + +. ++++ +. +

+++

+. + +. +=== +. +

===

+. + +Not enough characters: + +. +-- +** +__ +. +

-- +** +__

+. + +One to three spaces indent are allowed: + +. + *** + *** + *** +. +
+
+
+. + +Four spaces is too many: + +. + *** +. +
***
+
+. + +. +Foo + *** +. +

Foo +***

+. + +More than three characters may be used: + +. +_____________________________________ +. +
+. + +Spaces are allowed between the characters: + +. + - - - +. +
+. + +. + ** * ** * ** * ** +. +
+. + +. +- - - - +. +
+. + +Spaces are allowed at the end: + +. +- - - - +. +
+. + +However, no other characters may occur in the line: + +. +_ _ _ _ a + +a------ + +---a--- +. +

_ _ _ _ a

+

a------

+

---a---

+. + +It is required that all of the [non-space character]s be the same. +So, this is not a horizontal rule: + +. + *-* +. +

-

+. + +Horizontal rules do not need blank lines before or after: + +. +- foo +*** +- bar +. + +
+ +. + +Horizontal rules can interrupt a paragraph: + +. +Foo +*** +bar +. +

Foo

+
+

bar

+. + +If a line of dashes that meets the above conditions for being a +horizontal rule could also be interpreted as the underline of a [setext +header], the interpretation as a +[setext header] takes precedence. Thus, for example, +this is a setext header, not a paragraph followed by a horizontal rule: + +. +Foo +--- +bar +. +

Foo

+

bar

+. + +When both a horizontal rule and a list item are possible +interpretations of a line, the horizontal rule takes precedence: + +. +* Foo +* * * +* Bar +. + +
+ +. + +If you want a horizontal rule in a list item, use a different bullet: + +. +- Foo +- * * * +. + +. + +## ATX headers + +An [ATX header](@atx-header) +consists of a string of characters, parsed as inline content, between an +opening sequence of 1--6 unescaped `#` characters and an optional +closing sequence of any number of `#` characters. The opening sequence +of `#` characters cannot be followed directly by a +[non-space character]. +The optional closing sequence of `#`s must be preceded by a space and may be +followed by spaces only. The opening `#` character may be indented 0-3 +spaces. The raw contents of the header are stripped of leading and +trailing spaces before being parsed as inline content. The header level +is equal to the number of `#` characters in the opening sequence. + +Simple headers: + +. +# foo +## foo +### foo +#### foo +##### foo +###### foo +. +

foo

+

foo

+

foo

+

foo

+
foo
+
foo
+. + +More than six `#` characters is not a header: + +. +####### foo +. +

####### foo

+. + +A space is required between the `#` characters and the header's +contents. Note that many implementations currently do not require +the space. However, the space was required by the [original ATX +implementation](http://www.aaronsw.com/2002/atx/atx.py), and it helps +prevent things like the following from being parsed as headers: + +. +#5 bolt +. +

#5 bolt

+. + +This is not a header, because the first `#` is escaped: + +. +\## foo +. +

## foo

+. + +Contents are parsed as inlines: + +. +# foo *bar* \*baz\* +. +

foo bar *baz*

+. + +Leading and trailing blanks are ignored in parsing inline content: + +. +# foo +. +

foo

+. + +One to three spaces indentation are allowed: + +. + ### foo + ## foo + # foo +. +

foo

+

foo

+

foo

+. + +Four spaces are too much: + +. + # foo +. +
# foo
+
+. + +. +foo + # bar +. +

foo +# bar

+. + +A closing sequence of `#` characters is optional: + +. +## foo ## + ### bar ### +. +

foo

+

bar

+. + +It need not be the same length as the opening sequence: + +. +# foo ################################## +##### foo ## +. +

foo

+
foo
+. + +Spaces are allowed after the closing sequence: + +. +### foo ### +. +

foo

+. + +A sequence of `#` characters with a +[non-space character] following it +is not a closing sequence, but counts as part of the contents of the +header: + +. +### foo ### b +. +

foo ### b

+. + +The closing sequence must be preceded by a space: + +. +# foo# +. +

foo#

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

foo ###

+

foo ###

+

foo #

+. + +ATX headers need not be separated from surrounding content by blank +lines, and they can interrupt paragraphs: + +. +**** +## foo +**** +. +
+

foo

+
+. + +. +Foo bar +# baz +Bar foo +. +

Foo bar

+

baz

+

Bar foo

+. + +ATX headers can be empty: + +. +## +# +### ### +. +

+

+

+. + +## Setext headers + +A [setext header](@setext-header) +consists of a line of text, containing at least one +[non-space character], +with no more than 3 spaces indentation, followed by a [setext header +underline]. The line of text must be +one that, were it not followed by the setext header underline, +would be interpreted as part of a paragraph: it cannot be a code +block, header, blockquote, horizontal rule, or list. + +A [setext header underline](@setext-header-underline) is a sequence of +`=` characters or a sequence of `-` characters, with no more than 3 +spaces indentation and any number of trailing spaces. If a line +containing a single `-` can be interpreted as an +empty [list items], it should be interpreted this way +and not as a [setext header underline]. + +The header is a level 1 header if `=` characters are used in the +[setext header underline], and a level 2 +header if `-` characters are used. The contents of the header are the +result of parsing the first line as Markdown inline content. + +In general, a setext header need not be preceded or followed by a +blank line. However, it cannot interrupt a paragraph, so when a +setext header comes after a paragraph, a blank line is needed between +them. + +Simple examples: + +. +Foo *bar* +========= + +Foo *bar* +--------- +. +

Foo bar

+

Foo bar

+. + +The underlining can be any length: + +. +Foo +------------------------- + +Foo += +. +

Foo

+

Foo

+. + +The header content can be indented up to three spaces, and need +not line up with the underlining: + +. + Foo +--- + + Foo +----- + + Foo + === +. +

Foo

+

Foo

+

Foo

+. + +Four spaces indent is too much: + +. + Foo + --- + + Foo +--- +. +
Foo
+---
+
+Foo
+
+
+. + +The setext header underline can be indented up to three spaces, and +may have trailing spaces: + +. +Foo + ---- +. +

Foo

+. + +Four spaces is too much: + +. +Foo + --- +. +

Foo +---

+. + +The setext header underline cannot contain internal spaces: + +. +Foo += = + +Foo +--- - +. +

Foo += =

+

Foo

+
+. + +Trailing spaces in the content line do not cause a line break: + +. +Foo +----- +. +

Foo

+. + +Nor does a backslash at the end: + +. +Foo\ +---- +. +

Foo\

+. + +Since indicators of block structure take precedence over +indicators of inline structure, the following are setext headers: + +. +`Foo +---- +` + + +. +

`Foo

+

`

+

<a title="a lot

+

of dashes"/>

+. + +The setext header underline cannot be a [lazy continuation +line] in a list item or block quote: + +. +> Foo +--- +. +
+

Foo

+
+
+. + +. +- Foo +--- +. + +
+. + +A setext header cannot interrupt a paragraph: + +. +Foo +Bar +--- + +Foo +Bar +=== +. +

Foo +Bar

+
+

Foo +Bar +===

+. + +But in general a blank line is not required before or after: + +. +--- +Foo +--- +Bar +--- +Baz +. +
+

Foo

+

Bar

+

Baz

+. + +Setext headers cannot be empty: + +. + +==== +. +

====

+. + +Setext header text lines must not be interpretable as block +constructs other than paragraphs. So, the line of dashes +in these examples gets interpreted as a horizontal rule: + +. +--- +--- +. +
+
+. + +. +- foo +----- +. + +
+. + +. + foo +--- +. +
foo
+
+
+. + +. +> foo +----- +. +
+

foo

+
+
+. + +If you want a header with `> foo` as its literal text, you can +use backslash escapes: + +. +\> foo +------ +. +

> foo

+. + +## Indented code blocks + +An [indented code block](@indented-code-block) is composed of one or more +[indented chunk]s separated by blank lines. +An [indented chunk](@indented-chunk) is a sequence of non-blank lines, +each indented four or more spaces. The contents of the code block are +the literal contents of the lines, including trailing +[line ending]s, 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.) + +. + a simple + indented code block +. +
a simple
+  indented code block
+
+. + +The contents are literal text, and do not get parsed as Markdown: + +. + + *hi* + + - one +. +
<a/>
+*hi*
+
+- one
+
+. + +Here we have three chunks separated by blank lines: + +. + chunk1 + + chunk2 + + + + chunk3 +. +
chunk1
+
+chunk2
+
+
+
+chunk3
+
+. + +Any initial spaces beyond four will be included in the content, even +in interior blank lines: + +. + chunk1 + + chunk2 +. +
chunk1
+  
+  chunk2
+
+. + +An indented code block cannot interrupt a paragraph. (This +allows hanging indents and the like.) + +. +Foo + bar + +. +

Foo +bar

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

bar

+. + +And indented code can occur immediately before and after other kinds of +blocks: + +. +# Header + foo +Header +------ + foo +---- +. +

Header

+
foo
+
+

Header

+
foo
+
+
+. + +The first line can be indented more than four spaces: + +. + foo + bar +. +
    foo
+bar
+
+. + +Blank lines preceding or following an indented code block +are not included in it: + +. + + + foo + + +. +
foo
+
+. + +Trailing spaces are included in the code block's content: + +. + foo +. +
foo  
+
+. + + +## Fenced code blocks + +A [code fence](@code-fence) is a sequence +of at least three consecutive backtick characters (`` ` ``) or +tildes (`~`). (Tildes and backticks cannot be mixed.) +A [fenced code block](@fenced-code-block) +begins with a code fence, indented no more than three spaces. + +The line with the opening code fence may optionally contain some text +following the code fence; this is trimmed of leading and trailing +spaces and called the [info string](@info-string). +The [info string] may not contain any backtick +characters. (The reason for this restriction is that otherwise +some inline code would be incorrectly interpreted as the +beginning of a fenced code block.) + +The content of the code block consists of all subsequent lines, until +a closing [code fence] of the same type as the code block +began with (backticks or tildes), and with at least as many backticks +or tildes as the opening code fence. If the leading code fence is +indented N spaces, then up to N spaces of indentation are removed from +each line of the content (if present). (If a content line is not +indented, it is preserved unchanged. If it is indented less than N +spaces, all of the indentation is removed.) + +The closing code fence may be indented up to three spaces, and may be +followed only by spaces, which are ignored. If the end of the +containing block (or document) is reached and no closing code fence +has been found, the code block contains all of the lines after the +opening code fence until the end of the containing block (or +document). (An alternative spec would require backtracking in the +event that a closing code fence is not found. But this makes parsing +much less efficient, and there seems to be no real down side to the +behavior described here.) + +A fenced code block may interrupt a paragraph, and does not require +a blank line either before or after. + +The content of a code fence is treated as literal text, not parsed +as inlines. The first word of the [info string] is typically used to +specify the language of the code sample, and rendered in the `class` +attribute of the `code` tag. However, this spec does not mandate any +particular treatment of the [info string]. + +Here is a simple example with backticks: + +. +``` +< + > +``` +. +
<
+ >
+
+. + +With tildes: + +. +~~~ +< + > +~~~ +. +
<
+ >
+
+. + +The closing code fence must use the same character as the opening +fence: + +. +``` +aaa +~~~ +``` +. +
aaa
+~~~
+
+. + +. +~~~ +aaa +``` +~~~ +. +
aaa
+```
+
+. + +The closing code fence must be at least as long as the opening fence: + +. +```` +aaa +``` +`````` +. +
aaa
+```
+
+. + +. +~~~~ +aaa +~~~ +~~~~ +. +
aaa
+~~~
+
+. + +Unclosed code blocks are closed by the end of the document: + +. +``` +. +
+. + +. +````` + +``` +aaa +. +

+```
+aaa
+
+. + +A code block can have all empty lines as its content: + +. +``` + + +``` +. +

+  
+
+. + +A code block can be empty: + +. +``` +``` +. +
+. + +Fences can be indented. If the opening fence is indented, +content lines will have equivalent opening indentation removed, +if present: + +. + ``` + aaa +aaa +``` +. +
aaa
+aaa
+
+. + +. + ``` +aaa + aaa +aaa + ``` +. +
aaa
+aaa
+aaa
+
+. + +. + ``` + aaa + aaa + aaa + ``` +. +
aaa
+ aaa
+aaa
+
+. + +Four spaces indentation produces an indented code block: + +. + ``` + aaa + ``` +. +
```
+aaa
+```
+
+. + +Closing fences may be indented by 0-3 spaces, and their indentation +need not match that of the opening fence: + +. +``` +aaa + ``` +. +
aaa
+
+. + +. + ``` +aaa + ``` +. +
aaa
+
+. + +This is not a closing fence, because it is indented 4 spaces: + +. +``` +aaa + ``` +. +
aaa
+    ```
+
+. + + +Code fences (opening and closing) cannot contain internal spaces: + +. +``` ``` +aaa +. +

+aaa

+. + +. +~~~~~~ +aaa +~~~ ~~ +. +
aaa
+~~~ ~~
+
+. + +Fenced code blocks can interrupt paragraphs, and can be followed +directly by paragraphs, without a blank line between: + +. +foo +``` +bar +``` +baz +. +

foo

+
bar
+
+

baz

+. + +Other blocks can also occur before and after fenced code blocks +without an intervening blank line: + +. +foo +--- +~~~ +bar +~~~ +# baz +. +

foo

+
bar
+
+

baz

+. + +An [info string] can be provided after the opening code fence. +Opening and closing spaces will be stripped, and the first word, prefixed +with `language-`, is used as the value for the `class` attribute of the +`code` element within the enclosing `pre` element. + +. +```ruby +def foo(x) + return 3 +end +``` +. +
def foo(x)
+  return 3
+end
+
+. + +. +~~~~ ruby startline=3 $%@#$ +def foo(x) + return 3 +end +~~~~~~~ +. +
def foo(x)
+  return 3
+end
+
+. + +. +````; +```` +. +
+. + +[Info string]s for backtick code blocks cannot contain backticks: + +. +``` aa ``` +foo +. +

aa +foo

+. + +Closing code fences cannot have [info string]s: + +. +``` +``` aaa +``` +. +
``` aaa
+
+. + + +## HTML blocks + +An [HTML block tag](@html-block-tag) is +an [open tag] or [closing tag] whose tag +name is one of the following (case-insensitive): +`article`, `header`, `aside`, `hgroup`, `blockquote`, `hr`, `iframe`, +`body`, `li`, `map`, `button`, `object`, `canvas`, `ol`, `caption`, +`output`, `col`, `p`, `colgroup`, `pre`, `dd`, `progress`, `div`, +`section`, `dl`, `table`, `td`, `dt`, `tbody`, `embed`, `textarea`, +`fieldset`, `tfoot`, `figcaption`, `th`, `figure`, `thead`, `footer`, +`tr`, `form`, `ul`, `h1`, `h2`, `h3`, `h4`, `h5`, `h6`, `video`, +`script`, `style`. + +An [HTML block](@html-block) begins with an +[HTML block tag], [HTML comment], [processing instruction], +[declaration], or [CDATA section]. +It ends when a [blank line] or the end of the +input is encountered. The initial line may be indented up to three +spaces, and subsequent lines may have any indentation. The contents +of the HTML block are interpreted as raw HTML, and will not be escaped +in HTML output. + +Some simple examples: + +. + + + + +
+ hi +
+ +okay. +. + + + + +
+ hi +
+

okay.

+. + +. +
+ *hello* + +. +
+ *hello* + +. + +Here we have two HTML blocks with a Markdown paragraph between them: + +. +
+ +*Markdown* + +
+. +
+

Markdown

+
+. + +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: + +. +
+``` c +int x = 33; +``` +. +
+``` c +int x = 33; +``` +. + +A comment: + +. + +. + +. + +A processing instruction: + +. +'; +?> +. +'; +?> +. + +CDATA: + +. + +. + +. + +The opening tag can be indented 1-3 spaces, but not 4: + +. + + + +. + +
<!-- foo -->
+
+. + +An HTML block can interrupt a paragraph, and need not be preceded +by a blank line. + +. +Foo +
+bar +
+. +

Foo

+
+bar +
+. + +However, a following blank line is always needed, except at the end of +a document: + +. +
+bar +
+*foo* +. +
+bar +
+*foo* +. + +An incomplete HTML block tag may also start an HTML block: + +. +
The only restrictions are that block-level HTML elements — +> e.g. `
`, ``, `
`, `
`, etc. — must be separated from
+> surrounding content by blank lines, and the start and end tags of the
+> block should not be indented with tabs or spaces.
+
+In some ways Gruber's rule is more restrictive than the one given
+here:
+
+- It requires that an HTML block be preceded by a blank line.
+- It does not allow the start tag to be indented.
+- It requires a matching end tag, which it also does not allow to
+  be indented.
+
+Indeed, most Markdown implementations, including some of Gruber's
+own perl implementations, do not impose these restrictions.
+
+There is one respect, however, in which Gruber's rule is more liberal
+than the one given here, since it allows blank lines to occur inside
+an HTML block.  There are two reasons for disallowing them here.
+First, it removes the need to parse balanced tags, which is
+expensive and can require backtracking from the end of the document
+if no matching end tag is found. Second, it provides a very simple
+and flexible way of including Markdown content inside HTML tags:
+simply separate the Markdown from the HTML using blank lines:
+
+.
+

+
+*Emphasized* text.
+
+

+.
+

+
Emphasized text.

+

+.
+
+Compare:
+
+.
+

+*Emphasized* text.
+

+.
+

+*Emphasized* text.
+

+.
+
+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:
+
+.
+
+ + + + + + + +
+Hi +
+. + + + + +
+Hi +
+. + +Moreover, blank lines are usually not necessary and can be +deleted. The exception is inside `
` tags; here, one can
+replace the blank lines with `
` entities.
+
+So there is no important loss of expressive power with the new rule.
+
+## Link reference definitions
+
+A [link reference definition](@link-reference-definition)
+consists of a [link label], indented up to three spaces, followed
+by a colon (`:`), optional [whitespace] (including up to one
+[line ending]), a [link destination],
+optional [whitespace] (including up to one
+[line ending]), and an optional [link
+title], which if it is present must be separated
+from the [link destination] by [whitespace].
+No further [non-space character]s may occur on the line.
+
+A [link reference-definition]
+does not correspond to a structural element of a document.  Instead, it
+defines a label which can be used in [reference link]s
+and reference-style [images] elsewhere in the document.  [Link
+reference definitions] can come either before or after the links that use
+them.
+
+.
+[foo]: /url "title"
+
+[foo]
+.
+
foo

+.
+
+.
+   [foo]: 
+      /url  
+           'the title'  
+
+[foo]
+.
+
foo

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

+.
+
+.
+[Foo bar]:
+
+'title'
+
+[Foo bar]
+.
+
Foo bar

+.
+
+The title may be omitted:
+
+.
+[foo]:
+/url
+
+[foo]
+.
+
foo

+.
+
+The link destination may not be omitted:
+
+.
+[foo]:
+
+[foo]
+.
+
[foo]:

+
[foo]

+.
+
+A link can come before its corresponding definition:
+
+.
+[foo]
+
+[foo]: url
+.
+
foo

+.
+
+If there are several matching definitions, the first one takes
+precedence:
+
+.
+[foo]
+
+[foo]: first
+[foo]: second
+.
+
foo

+.
+
+As noted in the section on [Links], matching of labels is
+case-insensitive (see [matches]).
+
+.
+[FOO]: /url
+
+[Foo]
+.
+
Foo

+.
+
+.
+[ΑΓΩ]: /φου
+
+[αγω]
+.
+
αγω

+.
+
+Here is a link reference definition with no corresponding link.
+It contributes nothing to the document.
+
+.
+[foo]: /url
+.
+.
+
+This is not a link reference definition, because there are
+[non-space character]s after the title:
+
+.
+[foo]: /url "title" ok
+.
+
[foo]: /url "title" ok

+.
+
+This is not a link reference definition, because it is indented
+four spaces:
+
+.
+    [foo]: /url "title"
+
+[foo]
+.
+
[foo]: /url "title"
+

+
[foo]

+.
+
+This is not a link reference definition, because it occurs inside
+a code block:
+
+.
+```
+[foo]: /url
+```
+
+[foo]
+.
+
[foo]: /url
+

+
[foo]

+.
+
+A [link reference definition] cannot interrupt a paragraph.
+
+.
+Foo
+[bar]: /baz
+
+[bar]
+.
+
Foo
+[bar]: /baz

+
[bar]

+.
+
+However, it can directly follow other block elements, such as headers
+and horizontal rules, and it need not be followed by a blank line.
+
+.
+# [Foo]
+[foo]: /url
+> bar
+.
+
Foo

+

+
bar

+

+.
+
+Several [link reference definition]s
+can occur one after another, without intervening blank lines.
+
+.
+[foo]: /foo-url "foo"
+[bar]: /bar-url
+  "bar"
+[baz]: /baz-url
+
+[foo],
+[bar],
+[baz]
+.
+
foo,
+bar,
+baz

+.
+
+[Link reference definition]s can occur
+inside block containers, like lists and block quotations.  They
+affect the entire document, not just the container in which they
+are defined:
+
+.
+[foo]
+
+> [foo]: /url
+.
+
foo

+

+

+.
+
+
+## Paragraphs
+
+A sequence of non-blank lines that cannot be interpreted as other
+kinds of blocks forms a [paragraph](@paragraph).
+The contents of the paragraph are the result of parsing the
+paragraph's raw content as inlines.  The paragraph's raw content
+is formed by concatenating the lines and removing initial and final
+[whitespace].
+
+A simple example with two paragraphs:
+
+.
+aaa
+
+bbb
+.
+
aaa

+
bbb

+.
+
+Paragraphs can contain multiple lines, but no blank lines:
+
+.
+aaa
+bbb
+
+ccc
+ddd
+.
+
aaa
+bbb

+
ccc
+ddd

+.
+
+Multiple blank lines between paragraph have no effect:
+
+.
+aaa
+
+
+bbb
+.
+
aaa

+
bbb

+.
+
+Leading spaces are skipped:
+
+.
+  aaa
+ bbb
+.
+
aaa
+bbb

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

+.
+
+However, the first line may be indented at most three spaces,
+or an indented code block will be triggered:
+
+.
+   aaa
+bbb
+.
+
aaa
+bbb

+.
+
+.
+    aaa
+bbb
+.
+
aaa
+

+
bbb

+.
+
+Final spaces are stripped before inline parsing, so a paragraph
+that ends with two or more spaces will not end with a [hard line
+break]:
+
+.
+aaa     
+bbb     
+.
+
aaa

+bbb

+.
+
+## Blank lines
+
+[Blank line]s 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.
+
+.
+  
+
+aaa
+  
+
+# aaa
+
+  
+.
+
aaa

+
aaa

+.
+
+
+# Container blocks
+
+A [container block] is a block that has other
+blocks as its contents.  There are two basic kinds of container blocks:
+[block quotes] and [list items].
+[Lists] are meta-containers for [list items].
+
+We define the syntax for container blocks recursively.  The general
+form of the definition is:
+
+> If X is a sequence of blocks, then the result of
+> transforming X in such-and-such a way is a container of type Y
+> with these blocks as its content.
+
+So, we explain what counts as a block quote or list item by explaining
+how these can be *generated* from their contents. This should suffice
+to define the syntax, although it does not give a recipe for *parsing*
+these constructions.  (A recipe is provided below in the section entitled
+[A parsing strategy](#appendix-a-a-parsing-strategy).)
+
+## Block quotes
+
+A [block quote marker](@block-quote-marker)
+consists of 0-3 spaces of initial indent, plus (a) the character `>` together
+with a following space, or (b) a single character `>` not followed by a space.
+
+The following rules define [block quotes]:
+
+1.  **Basic case.**  If a string of lines *Ls* constitute a sequence
+    of blocks *Bs*, then the result of prepending a [block quote
+    marker] to the beginning of each line in *Ls*
+    is a [block quote](#block-quotes) containing *Bs*.
+
+2.  **Laziness.**  If a string of lines *Ls* constitute a [block
+    quote](#block-quotes) with contents *Bs*, then the result of deleting
+    the initial [block quote marker] from one or
+    more lines in which the next [non-space character] after the [block
+    quote marker] is [paragraph continuation
+    text] is a block quote with *Bs* as its content.
+    [Paragraph continuation text](@paragraph-continuation-text) is text
+    that will be parsed as part of the content of a paragraph, but does
+    not occur at the beginning of the paragraph.
+
+3.  **Consecutiveness.**  A document cannot contain two [block
+    quotes] in a row unless there is a [blank line] between them.
+
+Nothing else counts as a [block quote](#block-quotes).
+
+Here is a simple example:
+
+.
+> # Foo
+> bar
+> baz
+.
+

+
Foo

+
bar
+baz

+

+.
+
+The spaces after the `>` characters can be omitted:
+
+.
+># Foo
+>bar
+> baz
+.
+

+
Foo

+
bar
+baz

+

+.
+
+The `>` characters can be indented 1-3 spaces:
+
+.
+   > # Foo
+   > bar
+ > baz
+.
+

+
Foo

+
bar
+baz

+

+.
+
+Four spaces gives us a code block:
+
+.
+    > # Foo
+    > bar
+    > baz
+.
+
> # Foo
+> bar
+> baz
+

+.
+
+The Laziness clause allows us to omit the `>` before a
+paragraph continuation line:
+
+.
+> # Foo
+> bar
+baz
+.
+

+
Foo

+
bar
+baz

+

+.
+
+A block quote can contain some lazy and some non-lazy
+continuation lines:
+
+.
+> bar
+baz
+> foo
+.
+

+
bar
+baz
+foo

+

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

+
foo

+

+

+.
+
+.
+> - foo
+- bar
+.
+

+
    
+
  • foo
    • 
+

+

+
    
+
  • bar
    • 
+

+.
+
+.
+>     foo
+    bar
+.
+

+
foo
+

+

+
bar
+

+.
+
+.
+> ```
+foo
+```
+.
+

+

+

+
foo

+

+.
+
+A block quote can be empty:
+
+.
+>
+.
+

+

+.
+
+.
+>
+>  
+> 
+.
+

+

+.
+
+A block quote can have initial or final blank lines:
+
+.
+>
+> foo
+>  
+.
+

+
foo

+

+.
+
+A blank line always separates block quotes:
+
+.
+> foo
+
+> bar
+.
+

+
foo

+

+

+
bar

+

+.
+
+(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:
+
+.
+> foo
+> bar
+.
+

+
foo
+bar

+

+.
+
+To get a block quote with two paragraphs, use:
+
+.
+> foo
+>
+> bar
+.
+

+
foo

+
bar

+

+.
+
+Block quotes can interrupt paragraphs:
+
+.
+foo
+> bar
+.
+
foo

+

+
bar

+

+.
+
+In general, blank lines are not needed before or after block
+quotes:
+
+.
+> aaa
+***
+> bbb
+.
+

+
aaa

+

+

+

+
bbb

+

+.
+
+However, because of laziness, a blank line is needed between
+a block quote and a following paragraph:
+
+.
+> bar
+baz
+.
+

+
bar
+baz

+

+.
+
+.
+> bar
+
+baz
+.
+

+
bar

+

+
baz

+.
+
+.
+> bar
+>
+baz
+.
+

+
bar

+

+
baz

+.
+
+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:
+
+.
+> > > foo
+bar
+.
+

+

+

+
foo
+bar

+

+

+

+.
+
+.
+>>> foo
+> bar
+>>baz
+.
+

+

+

+
foo
+bar
+baz

+

+

+

+.
+
+When including an indented code block in a block quote,
+remember that the [block quote marker] includes
+both the `>` and a following space.  So *five spaces* are needed after
+the `>`:
+
+.
+>     code
+
+>    not code
+.
+

+
code
+

+

+

+
not code

+

+.
+
+
+## List items
+
+A [list marker](@list-marker) is a
+[bullet list marker] or an [ordered list marker].
+
+A [bullet list marker](@bullet-list-marker)
+is a `-`, `+`, or `*` character.
+
+An [ordered list marker](@ordered-list-marker)
+is a sequence of one of more digits (`0-9`), followed by either a
+`.` character or a `)` character.
+
+The following rules define [list items]:
+
+1.  **Basic case.**  If a sequence of lines *Ls* constitute a sequence of
+    blocks *Bs* starting with a [non-space character] and not separated
+    from each other by more than one blank line, and *M* is a list
+    marker *M* of width *W* followed by 0 < *N* < 5 spaces, then the result
+    of prepending *M* and the following spaces to the first line of
+    *Ls*, and indenting subsequent lines of *Ls* by *W + N* spaces, is a
+    list item with *Bs* as its contents.  The type of the list item
+    (bullet or ordered) is determined by the type of its list marker.
+    If the list item is ordered, then it is also assigned a start
+    number, based on the ordered list marker.
+
+For example, let *Ls* be the lines
+
+.
+A paragraph
+with two lines.
+
+    indented code
+
+> A block quote.
+.
+
A paragraph
+with two lines.

+
indented code
+

+

+
A block quote.

+

+.
+
+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*:
+
+.
+1.  A paragraph
+    with two lines.
+
+        indented code
+
+    > A block quote.
+.
+
    
+
  1. 
+
    A paragraph
+with two lines.
    
+
    indented code
+
    
+
    
+
    A block quote.
    
+
    
+
    2. 
+

+.
+
+The most important thing to notice is that the position of
+the text after the list marker determines how much indentation
+is needed in subsequent blocks in the list item.  If the list
+marker takes up two spaces, and there are three spaces between
+the list marker and the next [non-space character], then blocks
+must be indented five spaces in order to fall under the list
+item.
+
+Here are some examples showing how far content must be indented to be
+put under the list item:
+
+.
+- one
+
+ two
+.
+
    
+
  • one
    • 
+

+
two

+.
+
+.
+- one
+
+  two
+.
+
    
+
  • 
+
    one
    
+
    two
    
+
    • 
+

+.
+
+.
+ -    one
+
+     two
+.
+
    
+
  • one
    • 
+

+
 two
+

+.
+
+.
+ -    one
+
+      two
+.
+
    
+
  • 
+
    one
    
+
    two
    
+
    • 
+

+.
+
+It is tempting to think of this in terms of columns:  the continuation
+blocks must be indented at least to the column of the first
+[non-space character] after the list marker. However, that is not quite right.
+The spaces after the list marker determine how much relative indentation
+is needed.  Which column this indentation reaches will depend on
+how the list item is embedded in other constructions, as shown by
+this example:
+
+.
+   > > 1.  one
+>>
+>>     two
+.
+

+

+
    
+
  1. 
+
    one
    
+
    two
    
+
    2. 
+

+

+

+.
+
+Here `two` occurs in the same column as the list marker `1.`,
+but is actually contained in the list item, because there is
+sufficent 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:
+
+.
+>>- one
+>>
+  >  > two
+.
+

+

+
    
+
  • one
    • 
+

+
two

+

+

+.
+
+A list item may not contain blocks that are separated by more than
+one blank line.  Thus, two blank lines will end a list, unless the
+two blanks are contained in a [fenced code block].
+
+.
+- foo
+
+  bar
+
+- foo
+
+
+  bar
+
+- ```
+  foo
+
+
+  bar
+  ```
+
+- baz
+
+  + ```
+    foo
+
+
+    bar
+    ```
+.
+
    
+
  • 
+
    foo
    
+
    bar
    
+
    • 
+
  • 
+
    foo
    
+
    • 
+

+
bar

+
    
+
  • 
+
    foo
+
+
+bar
+
    
+
    • 
+
  • 
+
    baz
    
+
      
+
    • 
+
      foo
+
+
+bar
+
      
+
      • 
+
    
+
    • 
+

+.
+
+A list item may contain any kind of block:
+
+.
+1.  foo
+
+    ```
+    bar
+    ```
+
+    baz
+
+    > bam
+.
+
    
+
  1. 
+
    foo
    
+
    bar
+
    
+
    baz
    
+
    
+
    bam
    
+
    
+
    2. 
+

+.
+
+2.  **Item starting with indented code.**  If a sequence of lines *Ls*
+    constitute a sequence of blocks *Bs* starting with an indented code
+    block and not separated from each other by more than one blank line,
+    and *M* is a list marker *M* of width *W* followed by
+    one space, then the result of prepending *M* and the following
+    space to the first line of *Ls*, and indenting subsequent lines of
+    *Ls* by *W + 1* spaces, is a list item with *Bs* as its contents.
+    If a line is empty, then it need not be indented.  The type of the
+    list item (bullet or ordered) is determined by the type of its list
+    marker.  If the list item is ordered, then it is also assigned a
+    start number, based on the ordered list marker.
+
+An indented code block will have to be indented four spaces beyond
+the edge of the region where text will be included in the list item.
+In the following case that is 6 spaces:
+
+.
+- foo
+
+      bar
+.
+
    
+
  • 
+
    foo
    
+
    bar
+
    
+
    • 
+

+.
+
+And in this case it is 11 spaces:
+
+.
+  10.  foo
+
+           bar
+.
+
    
+
  1. 
+
    foo
    
+
    bar
+
    
+
    2. 
+

+.
+
+If the *first* block in the list item is an indented code block,
+then by rule #2, the contents must be indented *one* space after the
+list marker:
+
+.
+    indented code
+
+paragraph
+
+    more code
+.
+
indented code
+

+
paragraph

+
more code
+

+.
+
+.
+1.     indented code
+
+   paragraph
+
+       more code
+.
+
    
+
  1. 
+
    indented code
+
    
+
    paragraph
    
+
    more code
+
    
+
    2. 
+

+.
+
+Note that an additional space indent is interpreted as space
+inside the code block:
+
+.
+1.      indented code
+
+   paragraph
+
+       more code
+.
+
    
+
  1. 
+
     indented code
+
    
+
    paragraph
    
+
    more code
+
    
+
    2. 
+

+.
+
+Note that rules #1 and #2 only apply to two cases:  (a) cases
+in which the lines to be included in a list item begin with a
+[non-space character], and (b) cases in which
+they begin with an indented code
+block.  In a case like the following, where the first block begins with
+a three-space indent, the rules do not allow us to form a list item by
+indenting the whole thing and prepending a list marker:
+
+.
+   foo
+
+bar
+.
+
foo

+
bar

+.
+
+.
+-    foo
+
+  bar
+.
+
    
+
  • foo
    • 
+

+
bar

+.
+
+This is not a significant restriction, because when a block begins
+with 1-3 spaces indent, the indentation can always be removed without
+a change in interpretation, allowing rule #1 to be applied.  So, in
+the above case:
+
+.
+-  foo
+
+   bar
+.
+
    
+
  • 
+
    foo
    
+
    bar
    
+
    • 
+

+.
+
+3. **Empty list item.**  A [list marker] followed by a
+line containing only [whitespace] is a list item with no contents.
+
+Here is an empty bullet list item:
+
+.
+- foo
+-
+- bar
+.
+
    
+
  • foo
    • 
+
  • 
+
  • bar
    • 
+

+.
+
+It does not matter whether there are spaces following the [list marker]:
+
+.
+- foo
+-   
+- bar
+.
+
    
+
  • foo
    • 
+
  • 
+
  • bar
    • 
+

+.
+
+Here is an empty ordered list item:
+
+.
+1. foo
+2.
+3. bar
+.
+
    
+
  1. foo
    2. 
+
  2. 
+
  3. bar
    4. 
+

+.
+
+A list may start or end with an empty list item:
+
+.
+*
+.
+
    
+
  • 
+

+.
+
+4.  **Indentation.**  If a sequence of lines *Ls* constitutes a list item
+    according to rule #1, #2, or #3, then the result of indenting each line
+    of *L* by 1-3 spaces (the same for each line) also constitutes a
+    list item with the same contents and attributes.  If a line is
+    empty, then it need not be indented.
+
+Indented one space:
+
+.
+ 1.  A paragraph
+     with two lines.
+
+         indented code
+
+     > A block quote.
+.
+
    
+
  1. 
+
    A paragraph
+with two lines.
    
+
    indented code
+
    
+
    
+
    A block quote.
    
+
    
+
    2. 
+

+.
+
+Indented two spaces:
+
+.
+  1.  A paragraph
+      with two lines.
+
+          indented code
+
+      > A block quote.
+.
+
    
+
  1. 
+
    A paragraph
+with two lines.
    
+
    indented code
+
    
+
    
+
    A block quote.
    
+
    
+
    2. 
+

+.
+
+Indented three spaces:
+
+.
+   1.  A paragraph
+       with two lines.
+
+           indented code
+
+       > A block quote.
+.
+
    
+
  1. 
+
    A paragraph
+with two lines.
    
+
    indented code
+
    
+
    
+
    A block quote.
    
+
    
+
    2. 
+

+.
+
+Four spaces indent gives a code block:
+
+.
+    1.  A paragraph
+        with two lines.
+
+            indented code
+
+        > A block quote.
+.
+
1.  A paragraph
+    with two lines.
+
+        indented code
+
+    > A block quote.
+

+.
+
+
+5.  **Laziness.**  If a string of lines *Ls* constitute a [list
+    item](#list-items) with contents *Bs*, then the result of deleting
+    some or all of the indentation from one or more lines in which the
+    next [non-space character] after the indentation is
+    [paragraph continuation text] is a
+    list item with the same contents and attributes.  The unindented
+    lines are called
+    [lazy continuation line](@lazy-continuation-line)s.
+
+Here is an example with [lazy continuation line]s:
+
+.
+  1.  A paragraph
+with two lines.
+
+          indented code
+
+      > A block quote.
+.
+
    
+
  1. 
+
    A paragraph
+with two lines.
    
+
    indented code
+
    
+
    
+
    A block quote.
    
+
    
+
    2. 
+

+.
+
+Indentation can be partially deleted:
+
+.
+  1.  A paragraph
+    with two lines.
+.
+
    
+
  1. A paragraph
+with two lines.
    2. 
+

+.
+
+These examples show how laziness can work in nested structures:
+
+.
+> 1. > Blockquote
+continued here.
+.
+

+
    
+
  1. 
+
    
+
    Blockquote
+continued here.
    
+
    
+
    2. 
+

+

+.
+
+.
+> 1. > Blockquote
+> continued here.
+.
+

+
    
+
  1. 
+
    
+
    Blockquote
+continued here.
    
+
    
+
    2. 
+

+

+.
+
+
+6.  **That's all.** Nothing that is not counted as a list item by rules
+    #1--5 counts as a [list item](#list-items).
+
+The rules for sublists follow from the general rules above.  A sublist
+must be indented the same number of spaces a paragraph would need to be
+in order to be included in the list item.
+
+So, in this case we need two spaces indent:
+
+.
+- foo
+  - bar
+    - baz
+.
+
    
+
  • foo
+
      
+
    • bar
+
        
+
      • baz
        • 
+
      
+
      • 
+
    
+
    • 
+

+.
+
+One is not enough:
+
+.
+- foo
+ - bar
+  - baz
+.
+
    
+
  • foo
    • 
+
  • bar
    • 
+
  • baz
    • 
+

+.
+
+Here we need four, because the list marker is wider:
+
+.
+10) foo
+    - bar
+.
+
    
+
  1. foo
+
      
+
    • bar
      • 
+
    
+
    2. 
+

+.
+
+Three is not enough:
+
+.
+10) foo
+   - bar
+.
+
    
+
  1. foo
    2. 
+

+
    
+
  • bar
    • 
+

+.
+
+A list may be the first block in a list item:
+
+.
+- - foo
+.
+
    
+
  • 
+
      
+
    • foo
      • 
+
    
+
    • 
+

+.
+
+.
+1. - 2. foo
+.
+
    
+
  1. 
+
      
+
    • 
+
        
+
      1. foo
        2. 
+
      
+
      • 
+
    
+
    2. 
+

+.
+
+A list item can contain a header:
+
+.
+- # Foo
+- Bar
+  ---
+  baz
+.
+
    
+
  • 
+
    Foo
    
+
    • 
+
  • 
+
    Bar
    
+baz
    • 
+

+.
+
+### Motivation
+
+John Gruber's Markdown spec says the following about list items:
+
+1. "List markers typically start at the left margin, but may be indented
+   by up to three spaces. List markers must be followed by one or more
+   spaces or a tab."
+
+2. "To make lists look nice, you can wrap items with hanging indents....
+   But if you don't want to, you don't have to."
+
+3. "List items may consist of multiple paragraphs. Each subsequent
+   paragraph in a list item must be indented by either 4 spaces or one
+   tab."
+
+4. "It looks nice if you indent every line of the subsequent paragraphs,
+   but here again, Markdown will allow you to be lazy."
+
+5. "To put a blockquote within a list item, the blockquote's `>`
+   delimiters need to be indented."
+
+6. "To put a code block within a list item, the code block needs to be
+   indented twice — 8 spaces or two tabs."
+
+These rules specify that a paragraph under a list item must be indented
+four spaces (presumably, from the left margin, rather than the start of
+the list marker, but this is not said), and that code under a list item
+must be indented eight spaces instead of the usual four.  They also say
+that a block quote must be indented, but not by how much; however, the
+example given has four spaces indentation.  Although nothing is said
+about other kinds of block-level content, it is certainly reasonable to
+infer that *all* block elements under a list item, including other
+lists, must be indented four spaces.  This principle has been called the
+*four-space rule*.
+
+The four-space rule is clear and principled, and if the reference
+implementation `Markdown.pl` had followed it, it probably would have
+become the standard.  However, `Markdown.pl` allowed paragraphs and
+sublists to start with only two spaces indentation, at least on the
+outer level.  Worse, its behavior was inconsistent: a sublist of an
+outer-level list needed two spaces indentation, but a sublist of this
+sublist needed three spaces.  It is not surprising, then, that different
+implementations of Markdown have developed very different rules for
+determining what comes under a list item.  (Pandoc and python-Markdown,
+for example, stuck with Gruber's syntax description and the four-space
+rule, while discount, redcarpet, marked, PHP Markdown, and others
+followed `Markdown.pl`'s behavior more closely.)
+
+Unfortunately, given the divergences between implementations, there
+is no way to give a spec for list items that will be guaranteed not
+to break any existing documents.  However, the spec given here should
+correctly handle lists formatted with either the four-space rule or
+the more forgiving `Markdown.pl` behavior, provided they are laid out
+in a way that is natural for a human to read.
+
+The strategy here is to let the width and indentation of the list marker
+determine the indentation necessary for blocks to fall under the list
+item, rather than having a fixed and arbitrary number.  The writer can
+think of the body of the list item as a unit which gets indented to the
+right enough to fit the list marker (and any indentation on the list
+marker).  (The laziness rule, #5, then allows continuation lines to be
+unindented if needed.)
+
+This rule is superior, we claim, to any rule requiring a fixed level of
+indentation from the margin.  The four-space rule is clear but
+unnatural. It is quite unintuitive that
+
+``` markdown
+- foo
+
+  bar
+
+  - baz
+```
+
+should be parsed as two lists with an intervening paragraph,
+
+``` html
+
    
+
  • foo
    • 
+

+
bar

+
    
+
  • baz
    • 
+

+```
+
+as the four-space rule demands, rather than a single list,
+
+``` html
+
    
+
  • 
+
    foo
    
+
    bar
    
+
      
+
    • baz
      • 
+
    
+
    • 
+

+```
+
+The choice of four spaces is arbitrary.  It can be learned, but it is
+not likely to be guessed, and it trips up beginners regularly.
+
+Would it help to adopt a two-space rule?  The problem is that such
+a rule, together with the rule allowing 1--3 spaces indentation of the
+initial list marker, allows text that is indented *less than* the
+original list marker to be included in the list item. For example,
+`Markdown.pl` parses
+
+``` markdown
+   - one
+
+  two
+```
+
+as a single list item, with `two` a continuation paragraph:
+
+``` html
+
    
+
  • 
+
    one
    
+
    two
    
+
    • 
+

+```
+
+and similarly
+
+``` markdown
+>   - one
+>
+>  two
+```
+
+as
+
+``` html
+

+
    
+
  • 
+
    one
    
+
    two
    
+
    • 
+

+

+```
+
+This is extremely unintuitive.
+
+Rather than requiring a fixed indent from the margin, we could require
+a fixed indent (say, two spaces, or even one space) from the list marker (which
+may itself be indented).  This proposal would remove the last anomaly
+discussed.  Unlike the spec presented above, it would count the following
+as a list item with a subparagraph, even though the paragraph `bar`
+is not indented as far as the first paragraph `foo`:
+
+``` markdown
+ 10. foo
+
+   bar  
+```
+
+Arguably this text does read like a list item with `bar` as a subparagraph,
+which may count in favor of the proposal.  However, on this proposal indented
+code would have to be indented six spaces after the list marker.  And this
+would break a lot of existing Markdown, which has the pattern:
+
+``` markdown
+1.  foo
+
+        indented code
+```
+
+where the code is indented eight spaces.  The spec above, by contrast, will
+parse this text as expected, since the code block's indentation is measured
+from the beginning of `foo`.
+
+The one case that needs special treatment is a list item that *starts*
+with indented code.  How much indentation is required in that case, since
+we don't have a "first paragraph" to measure from?  Rule #2 simply stipulates
+that in such cases, we require one space indentation from the list marker
+(and then the normal four spaces for the indented code).  This will match the
+four-space rule in cases where the list marker plus its initial indentation
+takes four spaces (a common case), but diverge in other cases.
+
+## Lists
+
+A [list](@list) is a sequence of one or more
+list items [of the same type].  The list items
+may be separated by single [blank lines], but two
+blank lines end all containing lists.
+
+Two list items are [of the same type](@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](@ordered-list)
+if its constituent list items begin with
+[ordered list marker]s, and a
+[bullet list](@bullet-list) if its constituent list
+items begin with [bullet list marker]s.
+
+The [start number](@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](@loose) if it any of its constituent
+list items are separated by blank lines, or if any of its constituent
+list items directly contain two block-level elements with a blank line
+between them.  Otherwise a list is [tight](@tight).
+(The difference in HTML output is that paragraphs in a loose list are
+wrapped in `
` tags, while paragraphs in a tight list are not.)
+
+Changing the bullet or ordered list delimiter starts a new list:
+
+.
+- foo
+- bar
++ baz
+.
+
    
+
  • foo
    • 
+
  • bar
    • 
+

+
    
+
  • baz
    • 
+

+.
+
+.
+1. foo
+2. bar
+3) baz
+.
+
    
+
  1. foo
    2. 
+
  2. bar
    3. 
+

+
    
+
  1. baz
    2. 
+

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

+
    
+
  • bar
    • 
+
  • baz
    • 
+

+.
+
+`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.
+.
+
The number of windows in my house is

+
    
+
  1. The number of doors is 6.
    2. 
+

+.
+
+Oddly, `Markdown.pl` *does* allow a blockquote to interrupt a paragraph,
+even though the same considerations might apply.  We think that the two
+cases should be treated the same.  Here are two reasons for allowing
+lists to interrupt paragraphs:
+
+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](@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 `
` 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.
+
+Our adherence to the [principle of uniformity]
+thus inclines us to think that there are two coherent packages:
+
+1.  Require blank lines before *all* lists and blockquotes,
+    including lists that occur as sublists inside other list items.
+
+2.  Require blank lines in none of these places.
+
+[reStructuredText](http://docutils.sourceforge.net/rst.html) takes
+the first approach, for which there is much to be said.  But the second
+seems more consistent with established practice with Markdown.
+
+There can be blank lines between items, but two blank lines end
+a list:
+
+.
+- foo
+
+- bar
+
+
+- baz
+.
+
    
+
  • 
+
    foo
    
+
    • 
+
  • 
+
    bar
    
+
    • 
+

+
    
+
  • baz
    • 
+

+.
+
+As illustrated above in the section on [list items],
+two blank lines between blocks *within* a list item will also end a
+list:
+
+.
+- foo
+
+
+  bar
+- baz
+.
+
    
+
  • foo
    • 
+

+
bar

+
    
+
  • baz
    • 
+

+.
+
+Indeed, two blank lines will end *all* containing lists:
+
+.
+- foo
+  - bar
+    - baz
+
+
+      bim
+.
+
    
+
  • foo
+
      
+
    • bar
+
        
+
      • baz
        • 
+
      
+
      • 
+
    
+
    • 
+

+
  bim
+

+.
+
+Thus, two blank lines can be used to separate consecutive lists of
+the same type, or to separate a list from an indented code block
+that would otherwise be parsed as a subparagraph of the final list
+item:
+
+.
+- foo
+- bar
+
+
+- baz
+- bim
+.
+
    
+
  • foo
    • 
+
  • bar
    • 
+

+
    
+
  • baz
    • 
+
  • bim
    • 
+

+.
+
+.
+-   foo
+
+    notcode
+
+-   foo
+
+
+    code
+.
+
    
+
  • 
+
    foo
    
+
    notcode
    
+
    • 
+
  • 
+
    foo
    
+
    • 
+

+
code
+

+.
+
+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:
+
+.
+- a
+ - b
+  - c
+   - d
+  - e
+ - f
+- g
+.
+
    
+
  • a
    • 
+
  • b
    • 
+
  • c
    • 
+
  • d
    • 
+
  • e
    • 
+
  • f
    • 
+
  • g
    • 
+

+.
+
+This is a loose list, because there is a blank line between
+two of the list items:
+
+.
+- a
+- b
+
+- c
+.
+
    
+
  • 
+
    a
    
+
    • 
+
  • 
+
    b
    
+
    • 
+
  • 
+
    c
    
+
    • 
+

+.
+
+So is this, with a empty second item:
+
+.
+* a
+*
+
+* c
+.
+
    
+
  • 
+
    a
    
+
    • 
+
  • 
+
  • 
+
    c
    
+
    • 
+

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

+.
+
+.
+- a
+- b
+
+  [ref]: /url
+- d
+.
+
    
+
  • 
+
    a
    
+
    • 
+
  • 
+
    b
    
+
    • 
+
  • 
+
    d
    
+
    • 
+

+.
+
+This is a tight list, because the blank lines are in a code block:
+
+.
+- a
+- ```
+  b
+
+
+  ```
+- c
+.
+
    
+
  • a
    • 
+
  • 
+
    b
+
+
+
    
+
    • 
+
  • c
    • 
+

+.
+
+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:
+
+.
+- a
+  - b
+
+    c
+- d
+.
+
    
+
  • a
+
      
+
    • 
+
      b
      
+
      c
      
+
      • 
+
    
+
    • 
+
  • d
    • 
+

+.
+
+This is a tight list, because the blank line is inside the
+block quote:
+
+.
+* a
+  > b
+  >
+* c
+.
+
    
+
  • a
+
    
+
    b
    
+
    
+
    • 
+
  • c
    • 
+

+.
+
+This list is tight, because the consecutive block elements
+are not separated by blank lines:
+
+.
+- a
+  > b
+  ```
+  c
+  ```
+- d
+.
+
    
+
  • a
+
    
+
    b
    
+
    
+
    c
+
    
+
    • 
+
  • d
    • 
+

+.
+
+A single-paragraph list is tight:
+
+.
+- a
+.
+
    
+
  • a
    • 
+

+.
+
+.
+- a
+  - b
+.
+
    
+
  • a
+
      
+
    • b
      • 
+
    
+
    • 
+

+.
+
+This list is loose, because of the blank line between the
+two block elements in the list item:
+
+.
+1. ```
+   foo
+   ```
+
+   bar
+.
+
    
+
  1. 
+
    foo
+
    
+
    bar
    
+
    2. 
+

+.
+
+Here the outer list is loose, the inner list tight:
+
+.
+* foo
+  * bar
+
+  baz
+.
+
    
+
  • 
+
    foo
    
+
      
+
    • bar
      • 
+
    
+
    baz
    
+
    • 
+

+.
+
+.
+- a
+  - b
+  - c
+
+- d
+  - e
+  - f
+.
+
    
+
  • 
+
    a
    
+
      
+
    • b
      • 
+
    • c
      • 
+
    
+
    • 
+
  • 
+
    d
    
+
      
+
    • e
      • 
+
    • f
      • 
+
    
+
    • 
+

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

+.
+
+`hi` is parsed as code, leaving the backtick at the end as a literal
+backtick.
+
+## Backslash escapes
+
+Any ASCII punctuation character may be backslash-escaped:
+
+.
+\!\"\#\$\%\&\'\(\)\*\+\,\-\.\/\:\;\<\=\>\?\@\[\\\]\^\_\`\{\|\}\~
+.
+
!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~

+.
+
+Backslashes before other characters are treated as literal
+backslashes:
+
+.
+\→\A\a\ \3\φ\«
+.
+
\   \A\a\ \3\φ\«

+.
+
+Escaped characters are treated as regular characters and do
+not have their usual Markdown meanings:
+
+.
+\*not emphasized*
+\
 not a tag
+\[not a link](/foo)
+\`not code`
+1\. not a list
+\* not a list
+\# not a header
+\[foo]: /url "not a reference"
+.
+
*not emphasized*
+<br/> not a tag
+[not a link](/foo)
+`not code`
+1. not a list
+* not a list
+# not a header
+[foo]: /url "not a reference"

+.
+
+If a backslash is itself escaped, the following character is not:
+
+.
+\\*emphasis*
+.
+
\emphasis

+.
+
+A backslash at the end of the line is a [hard line break]:
+
+.
+foo\
+bar
+.
+
foo

+bar

+.
+
+Backslash escapes do not work in code blocks, code spans, autolinks, or
+raw HTML:
+
+.
+`` \[\` ``
+.
+
\[\`

+.
+
+.
+    \[\]
+.
+
\[\]
+

+.
+
+.
+~~~
+\[\]
+~~~
+.
+
\[\]
+

+.
+
+.
+
+.
+
http://example.com?find=\*

+.
+
+.
+
+.
+

+.
+
+But they work in all other contexts, including URLs and link titles,
+link references, and [info string]s in [fenced code block]s:
+
+.
+[foo](/bar\* "ti\*tle")
+.
+
foo

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

+.
+
+.
+``` foo\+bar
+foo
+```
+.
+
foo
+

+.
+
+
+## Entities
+
+With the goal of making this standard as HTML-agnostic as possible, all
+valid HTML entities (except in code blocks and code spans)
+are recognized as such and converted into unicode characters before
+they are stored in the AST. This means that renderers to formats other
+than HTML need not be HTML-entity aware.  HTML renderers may either escape
+unicode characters as entities or leave them as they are.  (However,
+`"`, `&`, `<`, and `>` must always be rendered as entities.)
+
+[Named entities](@name-entities) consist of `&`
++ any of the valid HTML5 entity names + `;`. The
+[following document](https://html.spec.whatwg.org/multipage/entities.json)
+is used as an authoritative source of the valid entity names and their
+corresponding codepoints.
+
+.
+  & © Æ Ď ¾ ℋ ⅆ ∲
+.
+
  & © Æ Ď ¾ ℋ ⅆ ∲

+.
+
+[Decimal entities](@decimal-entities)
+consist of `&#` + a string of 1--8 arabic digits + `;`. Again, these
+entities need to be recognised and tranformed into their corresponding
+UTF8 codepoints. Invalid Unicode codepoints will be written as the
+"unknown codepoint" character (`0xFFFD`)
+
+.
+# Ӓ Ϡ �
+.
+
# Ӓ Ϡ �

+.
+
+[Hexadecimal entities](@hexadecimal-entities)
+consist of `&#` + either `X` or `x` + a string of 1-8 hexadecimal digits
++ `;`. They will also be parsed and turned into their corresponding UTF8 values in the AST.
+
+.
+" ആ ಫ
+.
+
" ആ ಫ

+.
+
+Here are some nonentities:
+
+.
+  &x; &#; &#x; &ThisIsWayTooLongToBeAnEntityIsntIt; &hi?;
+.
+
&nbsp &x; &#; &#x; &ThisIsWayTooLongToBeAnEntityIsntIt; &hi?;

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

+.
+
+Strings that are not on the list of HTML5 named entities are not
+recognized as entities either:
+
+.
+&MadeUpEntity;
+.
+
&MadeUpEntity;

+.
+
+Entities are recognized in any context besides code spans or
+code blocks, including raw HTML, URLs, [link title]s, and
+[fenced code block] [info string]s:
+
+.
+
+.
+

+.
+
+.
+[foo](/föö "föö")
+.
+
foo

+.
+
+.
+[foo]
+
+[foo]: /föö "föö"
+.
+
foo

+.
+
+.
+``` föö
+foo
+```
+.
+
foo
+

+.
+
+Entities are treated as literal text in code spans and code blocks:
+
+.
+`föö`
+.
+
f&ouml;&ouml;

+.
+
+.
+    föfö
+.
+
f&ouml;f&ouml;
+

+.
+
+## Code spans
+
+A [backtick string](@backtick-string)
+is a string of one or more backtick characters (`` ` ``) that is neither
+preceded nor followed by a backtick.
+
+A [code span](@code-span) begins with a backtick string and ends with
+a backtick string of equal length.  The contents of the code span are
+the characters between the two backtick strings, with leading and
+trailing spaces and [line ending]s removed, and
+[whitespace] collapsed to single spaces.
+
+This is a simple code span:
+
+.
+`foo`
+.
+
foo

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

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

+.
+
+[Line ending]s are treated like spaces:
+
+.
+``
+foo
+``
+.
+
foo

+.
+
+Interior spaces and [line ending]s are collapsed into
+single spaces, just as they would be by a browser:
+
+.
+`foo   bar
+  baz`
+.
+
foo bar baz

+.
+
+Q: Why not just leave the spaces, since browsers will collapse them
+anyway?  A:  Because we might be targeting a non-HTML format, and we
+shouldn't rely on HTML-specific rendering assumptions.
+
+(Existing implementations differ in their treatment of internal
+spaces and [line ending]s.  Some, including `Markdown.pl` and
+`showdown`, convert an internal [line ending] into a
+`
` tag.  But this makes things difficult for those who like to
+hard-wrap their paragraphs, since a line break in the midst of a code
+span will cause an unintended line break in the output.  Others just
+leave internal spaces as they are, which is fine if only HTML is being
+targeted.)
+
+.
+`foo `` bar`
+.
+
foo `` bar

+.
+
+Note that backslash escapes do not work in code spans. All backslashes
+are treated literally:
+
+.
+`foo\`bar`
+.
+
foo\bar`

+.
+
+Backslash escapes are never needed, because one can always choose a
+string of *n* backtick characters as delimiters, where the code does
+not contain any strings of exactly *n* backtick characters.
+
+Code span backticks have higher precedence than any other inline
+constructs except HTML tags and autolinks.  Thus, for example, this is
+not parsed as emphasized text, since the second `*` is part of a code
+span:
+
+.
+*foo`*`
+.
+
*foo*

+.
+
+And this is not parsed as a link:
+
+.
+[not a `link](/foo`)
+.
+
[not a link](/foo)

+.
+
+Code spans, HTML tags, and autolinks have the same precedence.
+Thus, this is code:
+
+.
+``
+.
+
<a href="">`

+.
+
+But this is an HTML tag:
+
+.
+`
+.
+
`

+.
+
+And this is code:
+
+.
+``
+.
+
<http://foo.bar.baz>`

+.
+
+But this is an autolink:
+
+.
+`
+.
+
http://foo.bar.`baz`

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

+.
+
+.
+`foo
+.
+
`foo

+.
+
+## Emphasis and strong emphasis
+
+John Gruber's original [Markdown syntax
+description](http://daringfireball.net/projects/markdown/syntax#em) says:
+
+> Markdown treats asterisks (`*`) and underscores (`_`) as indicators of
+> emphasis. Text wrapped with one `*` or `_` will be wrapped with an HTML
+> `` tag; double `*`'s or `_`'s will be wrapped with an HTML ``
+> 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:
+
+``` markdown
+***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):
+
+``` markdown
+*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.)
+
+``` markdown
+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](@delimiter-run) is either
+a sequence of one or more `*` characters that is not preceded or
+followed by a `*` character, or a sequence of one or more `_`
+characters that is not preceded or followed by a `_` character.
+
+A [left-flanking delimiter run](@left-flanking-delimiter-run) is
+a [delimiter run] that is (a) not followed by [unicode whitespace],
+and (b) either not followed by a [punctuation character], or
+preceded by [unicode whitespace] or a [punctuation character].
+
+A [right-flanking delimiter run](@right-flanking-delimiter-run) is
+a [delimiter run] that is (a) not preceded by [unicode whitespace],
+and (b) either not preceded by a [punctuation character], or
+followed by [unicode whitespace] or a [punctuation character].
+
+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 right and right-flanking:
+
+    ```
+    abc***def
+    "abc"_"def"
+    ```
+
+  - Neither right 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](http://www.vfmd.org/vfmd-spec/specification/#procedure-for-identifying-emphasis-tags).
+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](@can-open-emphasis)
+    iff 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 not part of a [right-flanking delimiter run].
+
+3.  A single `*` character [can close emphasis](@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 not part of a [left-flanking delimiter run].
+
+5.  A double `**` [can open strong emphasis](@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 not part of a [right-flanking delimiter run].
+
+7.  A double `**` [can close strong emphasis](@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 not part of a [left-flanking delimiter run].
+
+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.  There must
+    be a nonempty sequence of inlines between the open delimiter
+    and the closing delimiter; these form the contents of the emphasis
+    inline.
+
+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.
+    There must be a nonempty sequence of inlines between the open
+    delimiter and the closing delimiter; these form the contents of
+    the strong emphasis inline.
+
+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 `...` is always preferred to
+    `...`.
+
+14. An interpretation `...` is always
+    preferred to `..`.
+
+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 `foo _bar baz_` rather
+    than `*foo bar* baz`.  For the same reason,
+    `**foo*bar**` is parsed as `foobar*`
+    rather than `foo*bar`.
+
+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 bar baz`
+    rather than `foo **bar baz`.
+
+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 `*foo*` rather than as
+    `[foo](bar)`.
+
+These rules can be illustrated through a series of examples.
+
+Rule 1:
+
+.
+*foo bar*
+.
+
foo bar

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

+.
+
+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]:
+
+.
+a*"foo"*
+.
+
a*"foo"*

+.
+
+Unicode nonbreaking spaces count as whitespace, too:
+
+.
+* a *
+.
+
* a *

+.
+
+Intraword emphasis with `*` is permitted:
+
+.
+foo*bar*
+.
+
foobar

+.
+
+.
+5*6*78
+.
+
5678

+.
+
+Rule 2:
+
+.
+_foo bar_
+.
+
foo bar

+.
+
+This is not emphasis, because the opening `_` is followed by
+whitespace:
+
+.
+_ foo bar_
+.
+
_ foo bar_

+.
+
+This is not emphasis, because the opening `_` is preceded
+by an alphanumeric and followed by punctuation:
+
+.
+a_"foo"_
+.
+
a_"foo"_

+.
+
+Emphasis with `_` is not allowed inside words:
+
+.
+foo_bar_
+.
+
foo_bar_

+.
+
+.
+5_6_78
+.
+
5_6_78

+.
+
+.
+пристаням_стремятся_
+.
+
пристаням_стремятся_

+.
+
+Here `_` does not generate emphasis, because the first delimiter run
+is right-flanking and the second left-flanking:
+
+.
+aa_"bb"_cc
+.
+
aa_"bb"_cc

+.
+
+Here there is no emphasis, because the delimiter runs are
+both left- and right-flanking:
+
+.
+"aa"_"bb"_"cc"
+.
+
"aa"_"bb"_"cc"

+.
+
+Rule 3:
+
+This is not emphasis, because the closing delimiter does
+not match the opening delimiter:
+
+.
+_foo*
+.
+
_foo*

+.
+
+This is not emphasis, because the closing `*` is preceded by
+whitespace:
+
+.
+*foo bar *
+.
+
*foo bar *

+.
+
+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]:
+
+.
+*(*foo)
+.
+
*(*foo)

+.
+
+The point of this restriction is more easily appreciated
+with this example:
+
+.
+*(*foo*)*
+.
+
(foo)

+.
+
+Intraword emphasis with `*` is allowed:
+
+.
+*foo*bar
+.
+
foobar

+.
+
+
+Rule 4:
+
+This is not emphasis, because the closing `_` is preceded by
+whitespace:
+
+.
+_foo bar _
+.
+
_foo bar _

+.
+
+This is not emphasis, because the second `_` is
+preceded by punctuation and followed by an alphanumeric:
+
+.
+_(_foo)
+.
+
_(_foo)

+.
+
+This is emphasis within emphasis:
+
+.
+_(_foo_)_
+.
+
(foo)

+.
+
+Intraword emphasis is disallowed for `_`:
+
+.
+_foo_bar
+.
+
_foo_bar

+.
+
+.
+_пристаням_стремятся
+.
+
_пристаням_стремятся

+.
+
+.
+_foo_bar_baz_
+.
+
foo_bar_baz

+.
+
+Rule 5:
+
+.
+**foo bar**
+.
+
foo bar

+.
+
+This is not strong emphasis, because the opening delimiter is
+followed by whitespace:
+
+.
+** foo bar**
+.
+
** foo bar**

+.
+
+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]:
+
+.
+a**"foo"**
+.
+
a**"foo"**

+.
+
+Intraword strong emphasis with `**` is permitted:
+
+.
+foo**bar**
+.
+
foobar

+.
+
+Rule 6:
+
+.
+__foo bar__
+.
+
foo bar

+.
+
+This is not strong emphasis, because the opening delimiter is
+followed by whitespace:
+
+.
+__ foo bar__
+.
+
__ foo bar__

+.
+
+This is not strong emphasis, because the opening `__` is preceded
+by an alphanumeric and followed by punctuation:
+
+.
+a__"foo"__
+.
+
a__"foo"__

+.
+
+Intraword strong emphasis is forbidden with `__`:
+
+.
+foo__bar__
+.
+
foo__bar__

+.
+
+.
+5__6__78
+.
+
5__6__78

+.
+
+.
+пристаням__стремятся__
+.
+
пристаням__стремятся__

+.
+
+.
+__foo, __bar__, baz__
+.
+
foo, bar, baz

+.
+
+Rule 7:
+
+This is not strong emphasis, because the closing delimiter is preceded
+by whitespace:
+
+.
+**foo bar **
+.
+
**foo bar **

+.
+
+(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:
+
+.
+**(**foo)
+.
+
**(**foo)

+.
+
+The point of this restriction is more easily appreciated
+with these examples:
+
+.
+*(**foo**)*
+.
+
(foo)

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

+.
+
+.
+**foo "*bar*" foo**
+.
+
foo "bar" foo

+.
+
+Intraword emphasis:
+
+.
+**foo**bar
+.
+
foobar

+.
+
+Rule 8:
+
+This is not strong emphasis, because the closing delimiter is
+preceded by whitespace:
+
+.
+__foo bar __
+.
+
__foo bar __

+.
+
+This is not strong emphasis, because the second `__` is
+preceded by punctuation and followed by an alphanumeric:
+
+.
+__(__foo)
+.
+
__(__foo)

+.
+
+The point of this restriction is more easily appreciated
+with this example:
+
+.
+_(__foo__)_
+.
+
(foo)

+.
+
+Intraword strong emphasis is forbidden with `__`:
+
+.
+__foo__bar
+.
+
__foo__bar

+.
+
+.
+__пристаням__стремятся
+.
+
__пристаням__стремятся

+.
+
+.
+__foo__bar__baz__
+.
+
foo__bar__baz

+.
+
+Rule 9:
+
+Any nonempty sequence of inline elements can be the contents of an
+emphasized span.
+
+.
+*foo [bar](/url)*
+.
+
foo bar

+.
+
+.
+*foo
+bar*
+.
+
foo
+bar

+.
+
+In particular, emphasis and strong emphasis can be nested
+inside emphasis:
+
+.
+_foo __bar__ baz_
+.
+
foo bar baz

+.
+
+.
+_foo _bar_ baz_
+.
+
foo bar baz

+.
+
+.
+__foo_ bar_
+.
+
foo bar

+.
+
+.
+*foo *bar**
+.
+
foo bar

+.
+
+.
+*foo **bar** baz*
+.
+
foo bar baz

+.
+
+But note:
+
+.
+*foo**bar**baz*
+.
+
foobarbaz

+.
+
+The difference is that in the preceding case, the internal delimiters
+[can close emphasis], while in the cases with spaces, they cannot.
+
+.
+***foo** bar*
+.
+
foo bar

+.
+
+.
+*foo **bar***
+.
+
foo bar

+.
+
+Note, however, that in the following case we get no strong
+emphasis, because the opening delimiter is closed by the first
+`*` before `bar`:
+
+.
+*foo**bar***
+.
+
foobar**

+.
+
+
+Indefinite levels of nesting are possible:
+
+.
+*foo **bar *baz* bim** bop*
+.
+
foo bar baz bim bop

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

+.
+
+There can be no empty emphasis or strong emphasis:
+
+.
+** is not an empty emphasis
+.
+
** is not an empty emphasis

+.
+
+.
+**** is not an empty strong emphasis
+.
+
**** is not an empty strong emphasis

+.
+
+
+Rule 10:
+
+Any nonempty sequence of inline elements can be the contents of an
+strongly emphasized span.
+
+.
+**foo [bar](/url)**
+.
+
foo bar

+.
+
+.
+**foo
+bar**
+.
+
foo
+bar

+.
+
+In particular, emphasis and strong emphasis can be nested
+inside strong emphasis:
+
+.
+__foo _bar_ baz__
+.
+
foo bar baz

+.
+
+.
+__foo __bar__ baz__
+.
+
foo bar baz

+.
+
+.
+____foo__ bar__
+.
+
foo bar

+.
+
+.
+**foo **bar****
+.
+
foo bar

+.
+
+.
+**foo *bar* baz**
+.
+
foo bar baz

+.
+
+But note:
+
+.
+**foo*bar*baz**
+.
+
foobarbaz**

+.
+
+The difference is that in the preceding case, the internal delimiters
+[can close emphasis], while in the cases with spaces, they cannot.
+
+.
+***foo* bar**
+.
+
foo bar

+.
+
+.
+**foo *bar***
+.
+
foo bar

+.
+
+Indefinite levels of nesting are possible:
+
+.
+**foo *bar **baz**
+bim* bop**
+.
+
foo bar baz
+bim bop

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

+.
+
+There can be no empty emphasis or strong emphasis:
+
+.
+__ is not an empty emphasis
+.
+
__ is not an empty emphasis

+.
+
+.
+____ is not an empty strong emphasis
+.
+
____ is not an empty strong emphasis

+.
+
+
+Rule 11:
+
+.
+foo ***
+.
+
foo ***

+.
+
+.
+foo *\**
+.
+
foo *

+.
+
+.
+foo *_*
+.
+
foo _

+.
+
+.
+foo *****
+.
+
foo *****

+.
+
+.
+foo **\***
+.
+
foo *

+.
+
+.
+foo **_**
+.
+
foo _

+.
+
+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:
+
+.
+**foo*
+.
+
*foo

+.
+
+.
+*foo**
+.
+
foo*

+.
+
+.
+***foo**
+.
+
*foo

+.
+
+.
+****foo*
+.
+
***foo

+.
+
+.
+**foo***
+.
+
foo*

+.
+
+.
+*foo****
+.
+
foo***

+.
+
+
+Rule 12:
+
+.
+foo ___
+.
+
foo ___

+.
+
+.
+foo _\__
+.
+
foo _

+.
+
+.
+foo _*_
+.
+
foo *

+.
+
+.
+foo _____
+.
+
foo _____

+.
+
+.
+foo __\___
+.
+
foo _

+.
+
+.
+foo __*__
+.
+
foo *

+.
+
+.
+__foo_
+.
+
_foo

+.
+
+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:
+
+.
+_foo__
+.
+
foo_

+.
+
+.
+___foo__
+.
+
_foo

+.
+
+.
+____foo_
+.
+
___foo

+.
+
+.
+__foo___
+.
+
foo_

+.
+
+.
+_foo____
+.
+
foo___

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

+.
+
+.
+*_foo_*
+.
+
foo

+.
+
+.
+__foo__
+.
+
foo

+.
+
+.
+_*foo*_
+.
+
foo

+.
+
+However, strong emphasis within strong emphasis is possible without
+switching delimiters:
+
+.
+****foo****
+.
+
foo

+.
+
+.
+____foo____
+.
+
foo

+.
+
+
+Rule 13 can be applied to arbitrarily long sequences of
+delimiters:
+
+.
+******foo******
+.
+
foo

+.
+
+Rule 14:
+
+.
+***foo***
+.
+
foo

+.
+
+.
+_____foo_____
+.
+
foo

+.
+
+Rule 15:
+
+.
+*foo _bar* baz_
+.
+
foo _bar baz_

+.
+
+.
+**foo*bar**
+.
+
foobar*

+.
+
+
+Rule 16:
+
+.
+**foo **bar baz**
+.
+
**foo bar baz

+.
+
+.
+*foo *bar baz*
+.
+
*foo bar baz

+.
+
+Rule 17:
+
+.
+*[bar*](/url)
+.
+
*bar*

+.
+
+.
+_foo [bar_](/url)
+.
+
_foo bar_

+.
+
+.
+*
+.
+
*

+.
+
+.
+**
+.
+
**

+.
+
+.
+__
+.
+
__

+.
+
+.
+*a `*`*
+.
+
a *

+.
+
+.
+_a `_`_
+.
+
a _

+.
+
+.
+**a
+.
+
**ahttp://foo.bar?q=**

+.
+
+.
+__a
+.
+
__ahttp://foo.bar?q=__

+.
+
+
+## Links
+
+A link contains [link text] (the visible text), a [link destination]
+(the URI that is the link destination), and optionally a [link title].
+There are two basic kinds of links in Markdown.  In [inline link]s the
+destination and title are given immediately after the link text.  In
+[reference link]s the destination and title are defined elsewhere in
+the document.
+
+A [link text](@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.
+
+- 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 span]s, [autolink]s, and raw [HTML tag]s 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](@link-destination) consists of either
+
+- a sequence of zero or more characters between an opening `<` and a
+  closing `>` that contains no line breaks or unescaped `<` or `>`
+  characters, or
+
+- a nonempty sequence of characters that does not include
+  ASCII space or control characters, and includes parentheses
+  only if (a) they are backslash-escaped or (b) they are part of
+  a balanced pair of unescaped parentheses that is not itself
+  inside a balanced pair of unescaped paretheses.
+
+A [link title](@link-title)  consists of either
+
+- a sequence of zero or more characters between straight double-quote
+  characters (`"`), including a `"` character only if it is
+  backslash-escaped, or
+
+- a sequence of zero or more characters between straight single-quote
+  characters (`'`), including a `'` character only if it is
+  backslash-escaped, or
+
+- a sequence of zero or more characters between matching parentheses
+  (`(...)`), including a `)` character only if it is backslash-escaped.
+
+An [inline link](@inline-link) consists of a [link text] followed immediately
+by a left parenthesis `(`, optional [whitespace], an optional
+[link destination], an optional [link title] separated from the link
+destination by [whitespace], optional [whitespace], and a right
+parenthesis `)`. The link's text consists of the inlines contained
+in the [link text] (excluding the enclosing square brackets).
+The link's URI consists of the link destination, excluding enclosing
+`<...>` if present, with backslash-escapes in effect as described
+above.  The link's title consists of the link title, excluding its
+enclosing delimiters, with backslash-escapes in effect as described
+above.
+
+Here is a simple inline link:
+
+.
+[link](/uri "title")
+.
+
link

+.
+
+The title may be omitted:
+
+.
+[link](/uri)
+.
+
link

+.
+
+Both the title and the destination may be omitted:
+
+.
+[link]()
+.
+
link

+.
+
+.
+[link](<>)
+.
+
link

+.
+
+If the destination contains spaces, it must be enclosed in pointy
+braces:
+
+.
+[link](/my uri)
+.
+
[link](/my uri)

+.
+
+.
+[link]()
+.
+
link

+.
+
+The destination cannot contain line breaks, even with pointy braces:
+
+.
+[link](foo
+bar)
+.
+
[link](foo
+bar)

+.
+
+.
+[link]()
+.
+
[link]()

+.
+
+One level of balanced parentheses is allowed without escaping:
+
+.
+[link]((foo)and(bar))
+.
+
link

+.
+
+However, if you have parentheses within parentheses, you need to escape
+or use the `<...>` form:
+
+.
+[link](foo(and(bar)))
+.
+
[link](foo(and(bar)))

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

+.
+
+.
+[link]()
+.
+
link

+.
+
+Parentheses and other symbols can also be escaped, as usual
+in Markdown:
+
+.
+[link](foo\)\:)
+.
+
link

+.
+
+URL-escaping should be left alone inside the destination, as all
+URL-escaped characters are also valid URL characters. HTML entities in
+the destination will be parsed into their UTF-8 codepoints, as usual, and
+optionally URL-escaped when written as HTML.
+
+.
+[link](foo%20bä)
+.
+
link

+.
+
+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:
+
+.
+[link]("title")
+.
+
link

+.
+
+Titles may be in single quotes, double quotes, or parentheses:
+
+.
+[link](/url "title")
+[link](/url 'title')
+[link](/url (title))
+.
+
link
+link
+link

+.
+
+Backslash escapes and entities may be used in titles:
+
+.
+[link](/url "title \""")
+.
+
link

+.
+
+Nested balanced quotes are not allowed without escaping:
+
+.
+[link](/url "title "and" title")
+.
+
[link](/url "title "and" title")

+.
+
+But it is easy to work around this by using a different quote type:
+
+.
+[link](/url 'title "and" title')
+.
+
link

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

+.
+
+But it is not allowed between the link text and the
+following parenthesis:
+
+.
+[link] (/uri)
+.
+
[link] (/uri)

+.
+
+The link text may contain balanced brackets, but not unbalanced ones,
+unless they are escaped:
+
+.
+[link [foo [bar]]](/uri)
+.
+
link [foo [bar]]

+.
+
+.
+[link] bar](/uri)
+.
+
[link] bar](/uri)

+.
+
+.
+[link [bar](/uri)
+.
+
[link bar

+.
+
+.
+[link \[bar](/uri)
+.
+
link [bar

+.
+
+The link text may contain inline content:
+
+.
+[link *foo **bar** `#`*](/uri)
+.
+
link foo bar #

+.
+
+.
+[![moon](moon.jpg)](/uri)
+.
+
moon

+.
+
+However, links may not contain other links, at any level of nesting.
+
+.
+[foo [bar](/uri)](/uri)
+.
+
[foo bar](/uri)

+.
+
+.
+[foo *[bar [baz](/uri)](/uri)*](/uri)
+.
+
[foo [bar baz](/uri)](/uri)

+.
+
+.
+![[[foo](uri1)](uri2)](uri3)
+.
+
[foo](uri2)

+.
+
+These cases illustrate the precedence of link text grouping over
+emphasis grouping:
+
+.
+*[foo*](/uri)
+.
+
*foo*

+.
+
+.
+[foo *bar](baz*)
+.
+
foo *bar

+.
+
+Note that brackets that *aren't* part of links do not take
+precedence:
+
+.
+*foo [bar* baz]
+.
+
foo [bar baz]

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

+.
+
+.
+[foo`](/uri)`
+.
+
[foo](/uri)

+.
+
+.
+[foo
+.
+
[foohttp://example.com?search=](uri)

+.
+
+There are three kinds of [reference link](@reference-link)s:
+[full](#full-reference-link), [collapsed](#collapsed-reference-link),
+and [shortcut](#shortcut-reference-link).
+
+A [full reference link](@full-reference-link)
+consists of a [link text], optional [whitespace], and a [link label]
+that [matches] a [link reference definition] elsewhere in the document.
+
+A [link label](@link-label)  begins with a left bracket (`[`) and ends
+with the first right bracket (`]`) that is not backslash-escaped.
+Unescaped square bracket characters are not allowed in
+[link label]s.  A link label can have at most 999
+characters inside the square brackets.
+
+One label [matches](@matches)
+another just in case their normalized forms are equal.  To normalize a
+label, perform the *unicode case fold* and collapse consecutive internal
+[whitespace] to a single space.  If there are multiple
+matching reference link definitions, the one that comes first in the
+document is used.  (It is desirable in such cases to emit a warning.)
+
+The contents of the first link label are parsed as inlines, which are
+used as the link's text.  The link's URI and title are provided by the
+matching [link reference definition].
+
+Here is a simple example:
+
+.
+[foo][bar]
+
+[bar]: /url "title"
+.
+
foo

+.
+
+The rules for the [link text] are the same as with
+[inline link]s.  Thus:
+
+The link text may contain balanced brackets, but not unbalanced ones,
+unless they are escaped:
+
+.
+[link [foo [bar]]][ref]
+
+[ref]: /uri
+.
+
link [foo [bar]]

+.
+
+.
+[link \[bar][ref]
+
+[ref]: /uri
+.
+
link [bar

+.
+
+The link text may contain inline content:
+
+.
+[link *foo **bar** `#`*][ref]
+
+[ref]: /uri
+.
+
link foo bar #

+.
+
+.
+[![moon](moon.jpg)][ref]
+
+[ref]: /uri
+.
+
moon

+.
+
+However, links may not contain other links, at any level of nesting.
+
+.
+[foo [bar](/uri)][ref]
+
+[ref]: /uri
+.
+
[foo bar]ref

+.
+
+.
+[foo *bar [baz][ref]*][ref]
+
+[ref]: /uri
+.
+
[foo bar baz]ref

+.
+
+(In the examples above, we have two [shortcut reference link]s
+instead of one [full reference link].)
+
+The following cases illustrate the precedence of link text grouping over
+emphasis grouping:
+
+.
+*[foo*][ref]
+
+[ref]: /uri
+.
+
*foo*

+.
+
+.
+[foo *bar][ref]
+
+[ref]: /uri
+.
+
foo *bar

+.
+
+These cases illustrate the precedence of HTML tags, code spans,
+and autolinks over link grouping:
+
+.
+[foo 
+
+[ref]: /uri
+.
+
[foo 

+.
+
+.
+[foo`][ref]`
+
+[ref]: /uri
+.
+
[foo][ref]

+.
+
+.
+[foo
+
+[ref]: /uri
+.
+
[foohttp://example.com?search=][ref]

+.
+
+Matching is case-insensitive:
+
+.
+[foo][BaR]
+
+[bar]: /url "title"
+.
+
foo

+.
+
+Unicode case fold is used:
+
+.
+[Толпой][Толпой] is a Russian word.
+
+[ТОЛПОЙ]: /url
+.
+
Толпой is a Russian word.

+.
+
+Consecutive internal [whitespace] is treated as one space for
+purposes of determining matching:
+
+.
+[Foo
+  bar]: /url
+
+[Baz][Foo bar]
+.
+
Baz

+.
+
+There can be [whitespace] between the [link text] and the [link label]:
+
+.
+[foo] [bar]
+
+[bar]: /url "title"
+.
+
foo

+.
+
+.
+[foo]
+[bar]
+
+[bar]: /url "title"
+.
+
foo

+.
+
+When there are multiple matching [link reference definition]s,
+the first is used:
+
+.
+[foo]: /url1
+
+[foo]: /url2
+
+[bar][foo]
+.
+
bar

+.
+
+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:
+
+.
+[bar][foo\!]
+
+[foo!]: /url
+.
+
[bar][foo!]

+.
+
+[Link label]s cannot contain brackets, unless they are
+backslash-escaped:
+
+.
+[foo][ref[]
+
+[ref[]: /uri
+.
+
[foo][ref[]

+
[ref[]: /uri

+.
+
+.
+[foo][ref[bar]]
+
+[ref[bar]]: /uri
+.
+
[foo][ref[bar]]

+
[ref[bar]]: /uri

+.
+
+.
+[[[foo]]]
+
+[[[foo]]]: /url
+.
+
[[[foo]]]

+
[[[foo]]]: /url

+.
+
+.
+[foo][ref\[]
+
+[ref\[]: /uri
+.
+
foo

+.
+
+A [collapsed reference link](@collapsed-reference-link)
+consists of a [link label] that [matches] a
+[link reference definition] elsewhere in the
+document, optional [whitespace], and the string `[]`.
+The contents of the first link label are parsed as inlines,
+which are used as the link's text.  The link's URI and title are
+provided by the matching reference link definition.  Thus,
+`[foo][]` is equivalent to `[foo][foo]`.
+
+.
+[foo][]
+
+[foo]: /url "title"
+.
+
foo

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

+.
+
+The link labels are case-insensitive:
+
+.
+[Foo][]
+
+[foo]: /url "title"
+.
+
Foo

+.
+
+
+As with full reference links, [whitespace] is allowed
+between the two sets of brackets:
+
+.
+[foo] 
+[]
+
+[foo]: /url "title"
+.
+
foo

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

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

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

+.
+
+The link labels are case-insensitive:
+
+.
+[Foo]
+
+[foo]: /url "title"
+.
+
Foo

+.
+
+A space after the link text should be preserved:
+
+.
+[foo] bar
+
+[foo]: /url
+.
+
foo bar

+.
+
+If you just want bracketed text, you can backslash-escape the
+opening bracket to avoid links:
+
+.
+\[foo]
+
+[foo]: /url "title"
+.
+
[foo]

+.
+
+Note that this is a link, because a link label ends with the first
+following closing bracket:
+
+.
+[foo*]: /url
+
+*[foo*]
+.
+
*foo*

+.
+
+Full references take precedence over shortcut references:
+
+.
+[foo][bar]
+
+[foo]: /url1
+[bar]: /url2
+.
+
foo

+.
+
+In the following case `[bar][baz]` is parsed as a reference,
+`[foo]` as normal text:
+
+.
+[foo][bar][baz]
+
+[baz]: /url
+.
+
[foo]bar

+.
+
+Here, though, `[foo][bar]` is parsed as a reference, since
+`[bar]` is defined:
+
+.
+[foo][bar][baz]
+
+[baz]: /url1
+[bar]: /url2
+.
+
foobaz

+.
+
+Here `[foo]` is not parsed as a shortcut reference, because it
+is followed by a link label (even though `[bar]` is not defined):
+
+.
+[foo][bar][baz]
+
+[baz]: /url1
+[foo]: /url2
+.
+
[foo]bar

+.
+
+
+## Images
+
+Syntax for images is like the syntax for links, with one
+difference. Instead of [link text], we have an
+[image description](@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.
+
+.
+![foo](/url "title")
+.
+
foo

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

+.
+
+.
+![foo ![bar](/url)](/url2)
+.
+
foo bar

+.
+
+.
+![foo [bar](/url)](/url2)
+.
+
foo bar

+.
+
+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 bar`.  Only the plain string
+content is rendered, without formatting.
+
+.
+![foo *bar*][]
+
+[foo *bar*]: train.jpg "train & tracks"
+.
+
foo bar

+.
+
+.
+![foo *bar*][foobar]
+
+[FOOBAR]: train.jpg "train & tracks"
+.
+
foo bar

+.
+
+.
+![foo](train.jpg)
+.
+
foo

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

+.
+
+.
+![foo]()
+.
+
foo

+.
+
+.
+![](/url)
+.
+

+.
+
+Reference-style:
+
+.
+![foo] [bar]
+
+[bar]: /url
+.
+
foo

+.
+
+.
+![foo] [bar]
+
+[BAR]: /url
+.
+
foo

+.
+
+Collapsed:
+
+.
+![foo][]
+
+[foo]: /url "title"
+.
+
foo

+.
+
+.
+![*foo* bar][]
+
+[*foo* bar]: /url "title"
+.
+
foo bar

+.
+
+The labels are case-insensitive:
+
+.
+![Foo][]
+
+[foo]: /url "title"
+.
+
Foo

+.
+
+As with full reference links, [whitespace] is allowed
+between the two sets of brackets:
+
+.
+![foo] 
+[]
+
+[foo]: /url "title"
+.
+
foo

+.
+
+Shortcut:
+
+.
+![foo]
+
+[foo]: /url "title"
+.
+
foo

+.
+
+.
+![*foo* bar]
+
+[*foo* bar]: /url "title"
+.
+
foo bar

+.
+
+Note that link labels cannot contain unescaped brackets:
+
+.
+![[foo]]
+
+[[foo]]: /url "title"
+.
+
![[foo]]

+
[[foo]]: /url "title"

+.
+
+The link labels are case-insensitive:
+
+.
+![Foo]
+
+[foo]: /url "title"
+.
+
Foo

+.
+
+If you just want bracketed text, you can backslash-escape the
+opening `!` and `[`:
+
+.
+\!\[foo]
+
+[foo]: /url "title"
+.
+
![foo]

+.
+
+If you want a link after a literal `!`, backslash-escape the
+`!`:
+
+.
+\![foo]
+
+[foo]: /url "title"
+.
+
!foo

+.
+
+## Autolinks
+
+[Autolink](@autolink)s 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](@uri-autolink) consists of `<`, followed by an
+[absolute URI] not containing `<`, followed by `>`.  It is parsed as
+a link to the URI, with the URI as the link's label.
+
+An [absolute URI](@absolute-uri),
+for these purposes, consists of a [scheme] followed by a colon (`:`)
+followed by zero or more characters other than ASCII
+[whitespace] and control characters, `<`, and `>`.  If
+the URI includes these characters, you must use percent-encoding
+(e.g. `%20` for a space).
+
+The following [schemes](@scheme)
+are recognized (case-insensitive):
+`coap`, `doi`, `javascript`, `aaa`, `aaas`, `about`, `acap`, `cap`,
+`cid`, `crid`, `data`, `dav`, `dict`, `dns`, `file`, `ftp`, `geo`, `go`,
+`gopher`, `h323`, `http`, `https`, `iax`, `icap`, `im`, `imap`, `info`,
+`ipp`, `iris`, `iris.beep`, `iris.xpc`, `iris.xpcs`, `iris.lwz`, `ldap`,
+`mailto`, `mid`, `msrp`, `msrps`, `mtqp`, `mupdate`, `news`, `nfs`,
+`ni`, `nih`, `nntp`, `opaquelocktoken`, `pop`, `pres`, `rtsp`,
+`service`, `session`, `shttp`, `sieve`, `sip`, `sips`, `sms`, `snmp`,`
+soap.beep`, `soap.beeps`, `tag`, `tel`, `telnet`, `tftp`, `thismessage`,
+`tn3270`, `tip`, `tv`, `urn`, `vemmi`, `ws`, `wss`, `xcon`,
+`xcon-userid`, `xmlrpc.beep`, `xmlrpc.beeps`, `xmpp`, `z39.50r`,
+`z39.50s`, `adiumxtra`, `afp`, `afs`, `aim`, `apt`,` attachment`, `aw`,
+`beshare`, `bitcoin`, `bolo`, `callto`, `chrome`,` chrome-extension`,
+`com-eventbrite-attendee`, `content`, `cvs`,` dlna-playsingle`,
+`dlna-playcontainer`, `dtn`, `dvb`, `ed2k`, `facetime`, `feed`,
+`finger`, `fish`, `gg`, `git`, `gizmoproject`, `gtalk`, `hcp`, `icon`,
+`ipn`, `irc`, `irc6`, `ircs`, `itms`, `jar`, `jms`, `keyparc`, `lastfm`,
+`ldaps`, `magnet`, `maps`, `market`,` message`, `mms`, `ms-help`,
+`msnim`, `mumble`, `mvn`, `notes`, `oid`, `palm`, `paparazzi`,
+`platform`, `proxy`, `psyc`, `query`, `res`, `resource`, `rmi`, `rsync`,
+`rtmp`, `secondlife`, `sftp`, `sgn`, `skype`, `smb`, `soldat`,
+`spotify`, `ssh`, `steam`, `svn`, `teamspeak`, `things`, `udp`,
+`unreal`, `ut2004`, `ventrilo`, `view-source`, `webcal`, `wtai`,
+`wyciwyg`, `xfire`, `xri`, `ymsgr`.
+
+Here are some valid autolinks:
+
+.
+
+.
+
http://foo.bar.baz

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

+.
+
+.
+
+.
+
irc://foo.bar:2233/baz

+.
+
+Uppercase is also fine:
+
+.
+
+.
+
MAILTO:FOO@BAR.BAZ

+.
+
+Spaces are not allowed in autolinks:
+
+.
+
+.
+
<http://foo.bar/baz bim>

+.
+
+An [email autolink](@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](@email-address),
+for these purposes, is anything that matches
+the [non-normative regex from the HTML5
+spec](https://html.spec.whatwg.org/multipage/forms.html#e-mail-state-(type=email)):
+
+    /^[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:
+
+.
+
+.
+
foo@bar.example.com

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

+.
+
+These are not autolinks:
+
+.
+<>
+.
+
<>

+.
+
+.
+
+.
+
<heck://bing.bong>

+.
+
+.
+< http://foo.bar >
+.
+
< http://foo.bar >

+.
+
+.
+
+.
+
<foo.bar.baz>

+.
+
+.
+
+.
+
<localhost:5001/foo>

+.
+
+.
+http://example.com
+.
+
http://example.com

+.
+
+.
+foo@bar.example.com
+.
+
foo@bar.example.com

+.
+
+## Raw HTML
+
+Text between `<` and `>` that looks like an HTML tag is parsed as a
+raw HTML tag and will be rendered in HTML without escaping.
+Tag and attribute names are not limited to current HTML tags,
+so custom tags (and even, say, DocBook tags) may be used.
+
+Here is the grammar for tags:
+
+A [tag name](@tag-name) consists of an ASCII letter
+followed by zero or more ASCII letters or digits.
+
+An [attribute](@attribute) consists of [whitespace],
+an [attribute name], and an optional
+[attribute value specification].
+
+An [attribute name](@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](@attribute-value-specification)
+consists of optional [whitespace],
+a `=` character, optional [whitespace], and an [attribute
+value].
+
+An [attribute value](@attribute-value)
+consists of an [unquoted attribute value],
+a [single-quoted attribute value], or a [double-quoted attribute value].
+
+An [unquoted attribute value](@unquoted-attribute-value)
+is a nonempty string of characters not
+including spaces, `"`, `'`, `=`, `<`, `>`, or `` ` ``.
+
+A [single-quoted attribute value](@single-quoted-attribute-value)
+consists of `'`, zero or more
+characters not including `'`, and a final `'`.
+
+A [double-quoted attribute value](@double-quoted-attribute-value)
+consists of `"`, zero or more
+characters not including `"`, and a final `"`.
+
+An [open tag](@open-tag) consists of a `<` character, a [tag name],
+zero or more [attributes], optional [whitespace], an optional `/`
+character, and a `>` character.
+
+A [closing tag](@closing-tag) consists of the string ``.
+
+An [HTML comment](@html-comment) consists of ``,
+where *text* does not start with `>` or `->`, does not end with `-`,
+and does not contain `--`.  (See the
+[HTML5 spec](http://www.w3.org/TR/html5/syntax.html#comments).)
+
+A [processing instruction](@processing-instruction)
+consists of the string ``, and the string
+`?>`.
+
+A [declaration](@declaration) consists of the
+string ``, and the character `>`.
+
+A [CDATA section](@cdata-section) consists of
+the string ``, and the string `]]>`.
+
+An [HTML tag](@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:
+
+.
+
+.
+

+.
+
+Empty elements:
+
+.
+
+.
+

+.
+
+[Whitespace] is allowed:
+
+.
+
+.
+

+.
+
+With attributes:
+
+.
+
+.
+

+.
+
+Illegal tag names, not parsed as HTML:
+
+.
+<33> <__>
+.
+
<33> <__>

+.
+
+Illegal attribute names:
+
+.
+
+.
+
<a h*#ref="hi">

+.
+
+Illegal attribute values:
+
+.
+
+.
+
</a href="foo">

+.
+
+Comments:
+
+.
+foo 
+.
+
foo 

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

+.
+
+Not comments:
+
+.
+foo  foo -->
+
+foo 
+.
+
foo <!--> foo -->

+
foo <!-- foo--->

+.
+
+Processing instructions:
+
+.
+foo 
+.
+
foo 

+.
+
+Declarations:
+
+.
+foo 
+.
+
foo 

+.
+
+CDATA sections:
+
+.
+foo &<]]>
+.
+
foo &<]]>

+.
+
+Entities are preserved in HTML attributes:
+
+.
+
+.
+

+.
+
+Backslash escapes do not work in HTML attributes:
+
+.
+
+.
+

+.
+
+.
+
+.
+
<a href=""">

+.
+
+## Hard line breaks
+
+A line break (not in a code span or HTML tag) that is preceded
+by two or more spaces and does not occur at the end of a block
+is parsed as a [hard line break](@hard-line-break) (rendered
+in HTML as a `
` tag):
+
+.
+foo  
+baz
+.
+
foo

+baz

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

+baz

+.
+
+More than two spaces can be used:
+
+.
+foo       
+baz
+.
+
foo

+baz

+.
+
+Leading spaces at the beginning of the next line are ignored:
+
+.
+foo  
+     bar
+.
+
foo

+bar

+.
+
+.
+foo\
+     bar
+.
+
foo

+bar

+.
+
+Line breaks can occur inside emphasis, links, and other constructs
+that allow inline content:
+
+.
+*foo  
+bar*
+.
+
foo

+bar

+.
+
+.
+*foo\
+bar*
+.
+
foo

+bar

+.
+
+Line breaks do not occur inside code spans
+
+.
+`code  
+span`
+.
+
code span

+.
+
+.
+`code\
+span`
+.
+
code\ span

+.
+
+or HTML tags:
+
+.
+
+.
+

+.
+
+.
+
+.
+

+.
+
+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:
+
+.
+foo\
+.
+
foo\

+.
+
+.
+foo  
+.
+
foo

+.
+
+.
+### foo\
+.
+
foo\

+.
+
+.
+### foo  
+.
+
foo

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

+.
+
+Spaces at the end of the line and beginning of the next line are
+removed:
+
+.
+foo 
+ baz
+.
+
foo
+baz

+.
+
+A conforming parser may render a soft line break in HTML either as a
+line break or as a space.
+
+A renderer may also provide an option to render soft line breaks
+as hard line breaks.
+
+## Textual content
+
+Any characters not given an interpretation by the above rules will
+be parsed as plain textual content.
+
+.
+hello $.;'there
+.
+
hello $.;'there

+.
+
+.
+Foo χρῆν
+.
+
Foo χρῆν

+.
+
+Internal spaces are preserved verbatim:
+
+.
+Multiple     spaces
+.
+
Multiple     spaces

+.
+
+
+
+# Appendix A: A parsing strategy {-}
+
+## 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 headers
+are parsed into sequences of Markdown inline elements (strings,
+code spans, links, emphasis, and so on), using the map of link
+references constructed in phase 1.
+
+## The document tree {-}
+
+At each point in processing, the document is represented as a tree of
+**blocks**.  The root of the tree is a `document` block.  The `document`
+may have any number of other blocks as **children**.  These children
+may, in turn, have other blocks as children.  The last child of a block
+is normally considered **open**, meaning that subsequent lines of input
+can alter its contents.  (Blocks that are not open are **closed**.)
+Here, for example, is a possible document tree, with the open blocks
+marked by arrows:
+
+``` 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"
+```
+
+## How source lines alter the document tree {-}
+
+Each line that is processed has an effect on this tree.  The line is
+analyzed and, depending on its contents, the document may be altered
+in one or more of the following ways:
+
+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.
+
+We can see how this works by considering how the tree above is
+generated by four lines of Markdown:
+
+``` markdown
+> Lorem ipsum dolor
+sit amet.
+> - Qui *quodsi iracundia*
+> - aliquando id
+```
+
+At the outset, our document model is just
+
+``` tree
+-> document
+```
+
+The first line of our text,
+
+``` markdown
+> 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`:
+
+``` tree
+-> document
+  -> block_quote
+    -> paragraph
+         "Lorem ipsum dolor"
+```
+
+The next line,
+
+``` markdown
+sit amet.
+```
+
+is a "lazy continuation" of the open `paragraph`, so it gets added
+to the paragraph's text:
+
+``` tree
+-> document
+  -> block_quote
+    -> paragraph
+         "Lorem ipsum dolor\nsit amet."
+```
+
+The third line,
+
+``` markdown
+> - 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`:
+
+``` tree
+-> 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,
+
+``` markdown
+> - 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:
+
+``` tree
+-> document
+  -> block_quote
+       paragraph
+         "Lorem ipsum dolor\nsit amet."
+    -> list (type=bullet tight=true bullet_char=-)
+         list_item
+           paragraph
+             "Qui *quodsi iracundia*"
+      -> list_item
+        -> paragraph
+             "aliquando id"
+```
+
+## From block structure to the final document {-}
+
+Once all of the input has been parsed, all open blocks are closed.
+
+We then "walk the tree," visiting every node, and parse raw
+string contents of paragraphs and headers as inlines.  At this
+point we have seen all the link reference definitions, so we can
+resolve reference links as we go.
+
+``` tree
+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`.
+
+The document can be rendered as HTML, or in any other format, given
+an appropriate renderer.
-- 
cgit v1.2.3