From 12e8343068b906f8b2afddc5569968a8a91fa5b0 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 29 Apr 2024 06:24:24 +0200 Subject: Adding upstream version 2.1.0. Signed-off-by: Daniel Baumann --- tests/test_cmark_spec/spec.md | 9756 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 9756 insertions(+) create mode 100644 tests/test_cmark_spec/spec.md (limited to 'tests/test_cmark_spec/spec.md') diff --git a/tests/test_cmark_spec/spec.md b/tests/test_cmark_spec/spec.md new file mode 100644 index 0000000..2d79f7b --- /dev/null +++ b/tests/test_cmark_spec/spec.md @@ -0,0 +1,9756 @@ +--- +title: CommonMark Spec +author: John MacFarlane +version: 0.30 +date: '2021-06-19' +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 for indicating formatting in email +and usenet posts. It was developed by John Gruber (with +help from Aaron Swartz) and released in 2004 in the form of a +[syntax description](http://daringfireball.net/projects/markdown/syntax) +and a Perl script (`Markdown.pl`) for converting Markdown to +HTML. In the next decade, dozens of implementations were +developed in many languages. Some extended the original +Markdown syntax with conventions for footnotes, tables, and +other document elements. Some allowed Markdown documents to be +rendered in formats other than HTML. Websites like Reddit, +StackOverflow, and GitHub had millions of people using Markdown. +And Markdown started to be used beyond the web, to author books, +articles, slide shows, letters, and lecture notes. + +What distinguishes Markdown from many other lightweight markup +syntaxes, which are often easier to write, is its readability. +As Gruber writes: + +> The overriding design goal for Markdown's formatting syntax is +> to make it as readable as possible. The idea is that a +> Markdown-formatted document should be publishable as-is, as +> plain text, without looking like it's been marked up with tags +> or formatting instructions. +> () + +The point can be illustrated by comparing a sample of +[AsciiDoc](http://www.methods.co.nz/asciidoc/) with +an equivalent sample of Markdown. Here is a sample of +AsciiDoc from the AsciiDoc manual: + +``` +1. List item one. ++ +List item one continued with a second paragraph followed by an +Indented block. ++ +................. +$ ls *.sh +$ mv *.sh ~/tmp +................. ++ +List item continued with a third paragraph. + +2. List item two continued with an open block. ++ +-- +This paragraph is part of the preceding list item. + +a. This list is nested and does not require explicit item +continuation. ++ +This paragraph is part of the preceding list item. + +b. List item b. + +This paragraph belongs to item two of the outer list. +-- +``` + +And here is the equivalent in Markdown: +``` +1. List item one. + + List item one continued with a second paragraph followed by an + Indented block. + + $ ls *.sh + $ mv *.sh ~/tmp + + List item continued with a third paragraph. + +2. List item two continued with an open block. + + This paragraph is part of the preceding list item. + + 1. This list is nested and does not require explicit item continuation. + + This paragraph is part of the preceding list item. + + 2. List item b. + + This paragraph belongs to item two of the outer list. +``` + +The AsciiDoc version is, arguably, easier to write. You don't need +to worry about indentation. But the Markdown version is much easier +to read. The nesting of list items is apparent to the eye in the +source, not just in the processed document. + +## 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 heading? + Most implementations do not require the blank line. However, + this can lead to unexpected results in hard-wrapped text, and + also to ambiguities in parsing (note that some implementations + put the heading inside the blockquote, while others do not). + (John Gruber has also spoken [in favor of requiring the blank + lines](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 thematic break in its second item, + or two lists separated by a thematic break? + + ``` 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 headings? (`Markdown.pl` does not + allow this, but does allow blockquotes to include headings.) + + ``` 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. + +Note that not every feature of the HTML samples is mandated by +the spec. For example, the spec says what counts as a link +destination, but it doesn't mandate that non-ASCII characters in +the URL be percent-encoded. To use the automatic tests, +implementers will need to provide a renderer that conforms to +the expectations of the spec examples (percent-encoding +non-ASCII characters in URLs). But a conforming implementation +can use a different renderer and may choose not to +percent-encode non-ASCII characters in URLs. + +This document is generated from a text file, `spec.txt`, written +in Markdown with a small extension for the side-by-side tests. +The script `tools/makespec.py` can be used to convert `spec.txt` into +HTML or CommonMark (which can then be converted into other formats). + +In the examples, the `→` character is used to represent tabs. + +# Preliminaries + +## Characters and lines + +Any sequence of [characters] is a valid CommonMark +document. + +A [character](@) is a Unicode code point. Although some +code points (for example, combining accents) do not correspond to +characters in an intuitive sense, all code points count as characters +for purposes of this spec. + +This spec does not specify an encoding; it thinks of lines as composed +of [characters] rather than bytes. A conforming parser may be limited +to a certain encoding. + +A [line](@) is a sequence of zero or more [characters] +other than line feed (`U+000A`) or carriage return (`U+000D`), +followed by a [line ending] or by the end of file. + +A [line ending](@) is a line feed (`U+000A`), a carriage return +(`U+000D`) not followed by a line feed, or a carriage return and a +following line feed. + +A line containing no characters, or a line containing only spaces +(`U+0020`) or tabs (`U+0009`), is called a [blank line](@). + +The following definitions of character classes will be used in this spec: + +A [Unicode whitespace character](@) is +any code point in the Unicode `Zs` general category, or a tab (`U+0009`), +line feed (`U+000A`), form feed (`U+000C`), or carriage return (`U+000D`). + +[Unicode whitespace](@) is a sequence of one or more +[Unicode whitespace characters]. + +A [tab](@) is `U+0009`. + +A [space](@) is `U+0020`. + +An [ASCII control character](@) is a character between `U+0000–1F` (both +including) or `U+007F`. + +An [ASCII punctuation character](@) +is `!`, `"`, `#`, `$`, `%`, `&`, `'`, `(`, `)`, +`*`, `+`, `,`, `-`, `.`, `/` (U+0021–2F), +`:`, `;`, `<`, `=`, `>`, `?`, `@` (U+003A–0040), +`[`, `\`, `]`, `^`, `_`, `` ` `` (U+005B–0060), +`{`, `|`, `}`, or `~` (U+007B–007E). + +A [Unicode punctuation character](@) is an [ASCII +punctuation character] or anything in +the general Unicode categories `Pc`, `Pd`, `Pe`, `Pf`, `Pi`, `Po`, or `Ps`. + +## Tabs + +Tabs in lines are not expanded to [spaces]. However, +in contexts where spaces help to define block structure, +tabs behave as if they were replaced by spaces with a tab stop +of 4 characters. + +Thus, for example, a tab can be used instead of four spaces +in an indented code block. (Note, however, that internal +tabs are passed through as literal tabs, not expanded to +spaces.) + +```````````````````````````````` example +→foo→baz→→bim +. +

foo→baz→→bim
+
+```````````````````````````````` + +```````````````````````````````` example + →foo→baz→→bim +. +
foo→baz→→bim
+
+```````````````````````````````` + +```````````````````````````````` example + a→a + ὐ→a +. +
a→a
+ὐ→a
+
+```````````````````````````````` + +In the following example, a continuation paragraph of a list +item is indented with a tab; this has exactly the same effect +as indentation with four spaces would: + +```````````````````````````````` example + - foo + +→bar +. +
    +
  • +

    foo

    +

    bar

    +
    • +
+```````````````````````````````` + +```````````````````````````````` example +- foo + +→→bar +. +
    +
  • +

    foo

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

Foo

+```````````````````````````````` + +```````````````````````````````` example +*→*→*→ +. +
+```````````````````````````````` + + +## Insecure characters + +For security reasons, the Unicode character `U+0000` must be replaced +with the REPLACEMENT CHARACTER (`U+FFFD`). + + +## Backslash escapes + +Any ASCII punctuation character may be backslash-escaped: + +```````````````````````````````` example +\!\"\#\$\%\&\'\(\)\*\+\,\-\.\/\:\;\<\=\>\?\@\[\\\]\^\_\`\{\|\}\~ +. +

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

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

\→\A\a\ \3\φ\«

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

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

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

\emphasis

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

foo
+bar

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

\[\`

+```````````````````````````````` + + +```````````````````````````````` example + \[\] +. +
\[\]
+
+```````````````````````````````` + + +```````````````````````````````` example +~~~ +\[\] +~~~ +. +
\[\]
+
+```````````````````````````````` + + +```````````````````````````````` example + +. +

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

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

foo

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

foo

+```````````````````````````````` + + +```````````````````````````````` example +``` foo\+bar +foo +``` +. +
foo
+
+```````````````````````````````` + + +## Entity and numeric character references + +Valid HTML entity references and numeric character references +can be used in place of the corresponding Unicode character, +with the following exceptions: + +- Entity and character references are not recognized in code + blocks and code spans. + +- Entity and character references cannot stand in place of + special characters that define structural elements in + CommonMark. For example, although `*` can be used + in place of a literal `*` character, `*` cannot replace + `*` in emphasis delimiters, bullet list markers, or thematic + breaks. + +Conforming CommonMark parsers need not store information about +whether a particular character was represented in the source +using a Unicode character or an entity reference. + +[Entity references](@) consist of `&` + any of the valid +HTML5 entity names + `;`. The +document +is used as an authoritative source for the valid entity +references and their corresponding code points. + +```````````````````````````````` example +  & © Æ Ď +¾ ℋ ⅆ +∲ ≧̸ +. +

  & © Æ Ď +¾ ℋ ⅆ +∲ ≧̸

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

# Ӓ Ϡ �

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

" ആ ಫ

+```````````````````````````````` + + +Here are some nonentities: + +```````````````````````````````` example +  &x; &#; &#x; +� +&#abcdef0; +&ThisIsNotDefined; &hi?; +. +

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

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

&copy

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

&MadeUpEntity;

+```````````````````````````````` + + +Entity and numeric character references are recognized in any +context besides code spans or code blocks, including +URLs, [link titles], and [fenced code block][] [info strings]: + +```````````````````````````````` example + +. + +```````````````````````````````` + + +```````````````````````````````` example +[foo](/föö "föö") +. +

foo

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

foo

+```````````````````````````````` + + +```````````````````````````````` example +``` föö +foo +``` +. +
foo
+
+```````````````````````````````` + + +Entity and numeric character references are treated as literal +text in code spans and code blocks: + +```````````````````````````````` example +`föö` +. +

f&ouml;&ouml;

+```````````````````````````````` + + +```````````````````````````````` example + föfö +. +
f&ouml;f&ouml;
+
+```````````````````````````````` + + +Entity and numeric character references cannot be used +in place of symbols indicating structure in CommonMark +documents. + +```````````````````````````````` example +*foo* +*foo* +. +

*foo* +foo

+```````````````````````````````` + +```````````````````````````````` example +* foo + +* foo +. +

* foo

+
    +
  • foo
    • +
+```````````````````````````````` + +```````````````````````````````` example +foo bar +. +

foo + +bar

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

→foo

+```````````````````````````````` + + +```````````````````````````````` example +[a](url "tit") +. +

[a](url "tit")

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

+++

+```````````````````````````````` + + +```````````````````````````````` example +=== +. +

===

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

-- +** +__

+```````````````````````````````` + + +Up to three spaces of indentation are allowed: + +```````````````````````````````` example + *** + *** + *** +. +
+
+
+```````````````````````````````` + + +Four spaces of indentation is too many: + +```````````````````````````````` example + *** +. +
***
+
+```````````````````````````````` + + +```````````````````````````````` example +Foo + *** +. +

Foo +***

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

_ _ _ _ a

+

a------

+

---a---

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

-

+```````````````````````````````` + + +Thematic breaks do not need blank lines before or after: + +```````````````````````````````` example +- foo +*** +- bar +. +
    +
  • foo
    • +
+
+
    +
  • bar
    • +
+```````````````````````````````` + + +Thematic breaks can interrupt a paragraph: + +```````````````````````````````` example +Foo +*** +bar +. +

Foo

+
+

bar

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

Foo

+

bar

+```````````````````````````````` + + +When both a thematic break and a list item are possible +interpretations of a line, the thematic break takes precedence: + +```````````````````````````````` example +* Foo +* * * +* Bar +. +
    +
  • Foo
    • +
+
+
    +
  • Bar
    • +
+```````````````````````````````` + + +If you want a thematic break in a list item, use a different bullet: + +```````````````````````````````` example +- Foo +- * * * +. +
    +
  • Foo
    • +
  • +
    +
    • +
+```````````````````````````````` + + +## ATX headings + +An [ATX heading](@) +consists of a string of characters, parsed as inline content, between an +opening sequence of 1--6 unescaped `#` characters and an optional +closing sequence of any number of unescaped `#` characters. +The opening sequence of `#` characters must be followed by spaces or tabs, or +by the end of line. The optional closing sequence of `#`s must be preceded by +spaces or tabs and may be followed by spaces or tabs only. The opening +`#` character may be preceded by up to three spaces of indentation. The raw +contents of the heading are stripped of leading and trailing space or tabs +before being parsed as inline content. The heading level is equal to the number +of `#` characters in the opening sequence. + +Simple headings: + +```````````````````````````````` example +# foo +## foo +### foo +#### foo +##### foo +###### foo +. +

foo

+

foo

+

foo

+

foo

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

####### foo

+```````````````````````````````` + + +At least one space or tab is required between the `#` characters and the +heading's contents, unless the heading is empty. Note that many +implementations currently do not require the space. However, the +space was required by the +[original ATX implementation](http://www.aaronsw.com/2002/atx/atx.py), +and it helps prevent things like the following from being parsed as +headings: + +```````````````````````````````` example +#5 bolt + +#hashtag +. +

#5 bolt

+

#hashtag

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

## foo

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

foo bar *baz*

+```````````````````````````````` + + +Leading and trailing spaces or tabs are ignored in parsing inline content: + +```````````````````````````````` example +# foo +. +

foo

+```````````````````````````````` + + +Up to three spaces of indentation are allowed: + +```````````````````````````````` example + ### foo + ## foo + # foo +. +

foo

+

foo

+

foo

+```````````````````````````````` + + +Four spaces of indentation is too many: + +```````````````````````````````` example + # foo +. +
# foo
+
+```````````````````````````````` + + +```````````````````````````````` example +foo + # bar +. +

foo +# bar

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

foo

+

bar

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

foo

+
foo
+```````````````````````````````` + + +Spaces or tabs are allowed after the closing sequence: + +```````````````````````````````` example +### foo ### +. +

foo

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

foo ### b

+```````````````````````````````` + + +The closing sequence must be preceded by a space or tab: + +```````````````````````````````` example +# foo# +. +

foo#

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

foo ###

+

foo ###

+

foo #

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

foo

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

Foo bar

+

baz

+

Bar foo

+```````````````````````````````` + + +ATX headings can be empty: + +```````````````````````````````` example +## +# +### ### +. +

+

+

+```````````````````````````````` + + +## Setext headings + +A [setext heading](@) consists of one or more +lines of text, not interrupted by a blank line, of which the first line does not +have more than 3 spaces of indentation, followed by +a [setext heading underline]. The lines of text must be such +that, were they not followed by the setext heading underline, +they would be interpreted as a paragraph: they cannot be +interpretable as a [code fence], [ATX heading][ATX headings], +[block quote][block quotes], [thematic break][thematic breaks], +[list item][list items], or [HTML block][HTML blocks]. + +A [setext heading underline](@) is a sequence of +`=` characters or a sequence of `-` characters, with no more than 3 +spaces of indentation and any number of trailing spaces or tabs. If a line +containing a single `-` can be interpreted as an +empty [list items], it should be interpreted this way +and not as a [setext heading underline]. + +The heading is a level 1 heading if `=` characters are used in +the [setext heading underline], and a level 2 heading if `-` +characters are used. The contents of the heading are the result +of parsing the preceding lines of text as CommonMark inline +content. + +In general, a setext heading need not be preceded or followed by a +blank line. However, it cannot interrupt a paragraph, so when a +setext heading comes after a paragraph, a blank line is needed between +them. + +Simple examples: + +```````````````````````````````` example +Foo *bar* +========= + +Foo *bar* +--------- +. +

Foo bar

+

Foo bar

+```````````````````````````````` + + +The content of the header may span more than one line: + +```````````````````````````````` example +Foo *bar +baz* +==== +. +

Foo bar +baz

+```````````````````````````````` + +The contents are the result of parsing the headings's raw +content as inlines. The heading's raw content is formed by +concatenating the lines and removing initial and final +spaces or tabs. + +```````````````````````````````` example + Foo *bar +baz*→ +==== +. +

Foo bar +baz

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

Foo

+

Foo

+```````````````````````````````` + + +The heading content can be preceded by up to three spaces of indentation, and +need not line up with the underlining: + +```````````````````````````````` example + Foo +--- + + Foo +----- + + Foo + === +. +

Foo

+

Foo

+

Foo

+```````````````````````````````` + + +Four spaces of indentation is too many: + +```````````````````````````````` example + Foo + --- + + Foo +--- +. +
Foo
+---
+
+Foo
+
+
+```````````````````````````````` + + +The setext heading underline can be preceded by up to three spaces of +indentation, and may have trailing spaces or tabs: + +```````````````````````````````` example +Foo + ---- +. +

Foo

+```````````````````````````````` + + +Four spaces of indentation is too many: + +```````````````````````````````` example +Foo + --- +. +

Foo +---

+```````````````````````````````` + + +The setext heading underline cannot contain internal spaces or tabs: + +```````````````````````````````` example +Foo += = + +Foo +--- - +. +

Foo += =

+

Foo

+
+```````````````````````````````` + + +Trailing spaces or tabs in the content line do not cause a hard line break: + +```````````````````````````````` example +Foo +----- +. +

Foo

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

Foo\

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

`Foo

+

`

+

<a title="a lot

+

of dashes"/>

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

Foo

+
+
+```````````````````````````````` + + +```````````````````````````````` example +> foo +bar +=== +. +
+

foo +bar +===

+
+```````````````````````````````` + + +```````````````````````````````` example +- Foo +--- +. +
    +
  • Foo
    • +
+
+```````````````````````````````` + + +A blank line is needed between a paragraph and a following +setext heading, since otherwise the paragraph becomes part +of the heading's content: + +```````````````````````````````` example +Foo +Bar +--- +. +

Foo +Bar

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

Foo

+

Bar

+

Baz

+```````````````````````````````` + + +Setext headings cannot be empty: + +```````````````````````````````` example + +==== +. +

====

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

foo

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

> foo

+```````````````````````````````` + + +**Compatibility note:** Most existing Markdown implementations +do not allow the text of setext headings to span multiple lines. +But there is no consensus about how to interpret + +``` markdown +Foo +bar +--- +baz +``` + +One can find four different interpretations: + +1. paragraph "Foo", heading "bar", paragraph "baz" +2. paragraph "Foo bar", thematic break, paragraph "baz" +3. paragraph "Foo bar --- baz" +4. heading "Foo bar", paragraph "baz" + +We find interpretation 4 most natural, and interpretation 4 +increases the expressive power of CommonMark, by allowing +multiline headings. Authors who want interpretation 1 can +put a blank line after the first paragraph: + +```````````````````````````````` example +Foo + +bar +--- +baz +. +

Foo

+

bar

+

baz

+```````````````````````````````` + + +Authors who want interpretation 2 can put blank lines around +the thematic break, + +```````````````````````````````` example +Foo +bar + +--- + +baz +. +

Foo +bar

+
+

baz

+```````````````````````````````` + + +or use a thematic break that cannot count as a [setext heading +underline], such as + +```````````````````````````````` example +Foo +bar +* * * +baz +. +

Foo +bar

+
+

baz

+```````````````````````````````` + + +Authors who want interpretation 3 can use backslash escapes: + +```````````````````````````````` example +Foo +bar +\--- +baz +. +

Foo +bar +--- +baz

+```````````````````````````````` + + +## Indented code blocks + +An [indented code block](@) is composed of one or more +[indented chunks] separated by blank lines. +An [indented chunk](@) is a sequence of non-blank lines, +each preceded by four or more spaces of indentation. The contents of the code +block are the literal contents of the lines, including trailing +[line endings], minus four spaces of indentation. +An indented code block has no [info string]. + +An indented code block cannot interrupt a paragraph, so there must be +a blank line between a paragraph and a following indented code block. +(A blank line is not needed, however, between a code block and a following +paragraph.) + +```````````````````````````````` example + a simple + indented code block +. +
a simple
+  indented code block
+
+```````````````````````````````` + + +If there is any ambiguity between an interpretation of indentation +as a code block and as indicating that material belongs to a [list +item][list items], the list item interpretation takes precedence: + +```````````````````````````````` example + - foo + + bar +. +
    +
  • +

    foo

    +

    bar

    +
    • +
+```````````````````````````````` + + +```````````````````````````````` example +1. foo + + - bar +. +
    +
  1. +

    foo

    +
      +
    • bar
      • +
    +
    2. +
+```````````````````````````````` + + + +The contents of a code block are literal text, and do not get parsed +as Markdown: + +```````````````````````````````` example + + *hi* + + - one +. +
<a/>
+*hi*
+
+- one
+
+```````````````````````````````` + + +Here we have three chunks separated by blank lines: + +```````````````````````````````` example + chunk1 + + chunk2 + + + + chunk3 +. +
chunk1
+
+chunk2
+
+
+
+chunk3
+
+```````````````````````````````` + + +Any initial spaces or tabs beyond four spaces of indentation will be included in +the content, even in interior blank lines: + +```````````````````````````````` example + chunk1 + + chunk2 +. +
chunk1
+  
+  chunk2
+
+```````````````````````````````` + + +An indented code block cannot interrupt a paragraph. (This +allows hanging indents and the like.) + +```````````````````````````````` example +Foo + bar + +. +

Foo +bar

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

bar

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

Heading

+
foo
+
+

Heading

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

foo

+```````````````````````````````` + +The closing code fence must use the same character as the opening +fence: + +```````````````````````````````` example +``` +aaa +~~~ +``` +. +
aaa
+~~~
+
+```````````````````````````````` + + +```````````````````````````````` example +~~~ +aaa +``` +~~~ +. +
aaa
+```
+
+```````````````````````````````` + + +The closing code fence must be at least as long as the opening fence: + +```````````````````````````````` example +```` +aaa +``` +`````` +. +
aaa
+```
+
+```````````````````````````````` + + +```````````````````````````````` example +~~~~ +aaa +~~~ +~~~~ +. +
aaa
+~~~
+
+```````````````````````````````` + + +Unclosed code blocks are closed by the end of the document +(or the enclosing [block quote][block quotes] or [list item][list items]): + +```````````````````````````````` example +``` +. +
+```````````````````````````````` + + +```````````````````````````````` example +````` + +``` +aaa +. +

+```
+aaa
+
+```````````````````````````````` + + +```````````````````````````````` example +> ``` +> aaa + +bbb +. +
+
aaa
+
+
+

bbb

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

+  
+
+```````````````````````````````` + + +A code block can be empty: + +```````````````````````````````` example +``` +``` +. +
+```````````````````````````````` + + +Fences can be indented. If the opening fence is indented, +content lines will have equivalent opening indentation removed, +if present: + +```````````````````````````````` example + ``` + aaa +aaa +``` +. +
aaa
+aaa
+
+```````````````````````````````` + + +```````````````````````````````` example + ``` +aaa + aaa +aaa + ``` +. +
aaa
+aaa
+aaa
+
+```````````````````````````````` + + +```````````````````````````````` example + ``` + aaa + aaa + aaa + ``` +. +
aaa
+ aaa
+aaa
+
+```````````````````````````````` + + +Four spaces of indentation is too many: + +```````````````````````````````` example + ``` + aaa + ``` +. +
```
+aaa
+```
+
+```````````````````````````````` + + +Closing fences may be preceded by up to three spaces of indentation, and their +indentation need not match that of the opening fence: + +```````````````````````````````` example +``` +aaa + ``` +. +
aaa
+
+```````````````````````````````` + + +```````````````````````````````` example + ``` +aaa + ``` +. +
aaa
+
+```````````````````````````````` + + +This is not a closing fence, because it is indented 4 spaces: + +```````````````````````````````` example +``` +aaa + ``` +. +
aaa
+    ```
+
+```````````````````````````````` + + + +Code fences (opening and closing) cannot contain internal spaces or tabs: + +```````````````````````````````` example +``` ``` +aaa +. +

+aaa

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

foo

+
bar
+
+

baz

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

foo

+
bar
+
+

baz

+```````````````````````````````` + + +An [info string] can be provided after the opening code fence. +Although this spec doesn't mandate any particular treatment of +the info string, the first word is typically used to specify +the language of the code block. In HTML output, the language is +normally indicated by adding a class to the `code` element consisting +of `language-` followed by the language name. + +```````````````````````````````` example +```ruby +def foo(x) + return 3 +end +``` +. +
def foo(x)
+  return 3
+end
+
+```````````````````````````````` + + +```````````````````````````````` example +~~~~ ruby startline=3 $%@#$ +def foo(x) + return 3 +end +~~~~~~~ +. +
def foo(x)
+  return 3
+end
+
+```````````````````````````````` + + +```````````````````````````````` example +````; +```` +. +
+```````````````````````````````` + + +[Info strings] for backtick code blocks cannot contain backticks: + +```````````````````````````````` example +``` aa ``` +foo +. +

aa +foo

+```````````````````````````````` + + +[Info strings] for tilde code blocks can contain backticks and tildes: + +```````````````````````````````` example +~~~ aa ``` ~~~ +foo +~~~ +. +
foo
+
+```````````````````````````````` + + +Closing code fences cannot have [info strings]: + +```````````````````````````````` example +``` +``` aaa +``` +. +
``` aaa
+
+```````````````````````````````` + + + +## HTML blocks + +An [HTML block](@) is a group of lines that is treated +as raw HTML (and will not be escaped in HTML output). + +There are seven kinds of [HTML block], which can be defined by their +start and end conditions. The block begins with a line that meets a +[start condition](@) (after up to three optional spaces of indentation). +It ends with the first subsequent line that meets a matching +[end condition](@), or the last line of the document, or the last line of +the [container block](#container-blocks) containing the current HTML +block, if no line is encountered that meets the [end condition]. If +the first line meets both the [start condition] and the [end +condition], the block will contain just that line. + +1. **Start condition:** line begins with the string ``, or the end of the line.\ +**End condition:** line contains an end tag +``, ``, ``, or `` (case-insensitive; it +need not match the start tag). + +2. **Start condition:** line begins with the string ``. + +3. **Start condition:** line begins with the string ``. + +4. **Start condition:** line begins with the string ``. + +5. **Start condition:** line begins with the string +``. + +6. **Start condition:** line begins the string `<` or ``, or +the string `/>`.\ +**End condition:** line is followed by a [blank line]. + +7. **Start condition:** line begins with a complete [open tag] +(with any [tag name] other than `pre`, `script`, +`style`, or `textarea`) or a complete [closing tag], +followed by zero or more spaces and tabs, followed by the end of the line.\ +**End condition:** line is followed by a [blank line]. + +HTML blocks continue until they are closed by their appropriate +[end condition], or the last line of the document or other [container +block](#container-blocks). This means any HTML **within an HTML +block** that might otherwise be recognised as a start condition will +be ignored by the parser and passed through as-is, without changing +the parser's state. + +For instance, `
` within an HTML block started by `` will not affect
+the parser state; as the HTML block was started in by start condition 6, it
+will end at any blank line. This can be surprising:
+
+```````````````````````````````` example
+

+
+**Hello**,
+
+_world_.
+

+

+.
+

+
+**Hello**,
+
world.
+

+

+````````````````````````````````
+
+In this case, the HTML block is terminated by the blank line — the `**Hello**`
+text remains verbatim — and regular parsing resumes, with a paragraph,
+emphasised `world` and inline and block HTML following.
+
+All types of [HTML blocks] except type 7 may interrupt
+a paragraph.  Blocks of type 7 may not interrupt a paragraph.
+(This restriction is intended to prevent unwanted interpretation
+of long tags inside a wrapped paragraph as starting HTML blocks.)
+
+Some simple examples follow.  Here are some basic HTML blocks
+of type 6:
+
+```````````````````````````````` example
+
+  
+    
+  
+

+           hi
+    

+
+okay.
+.
+
+  
+    
+  
+

+           hi
+    

+
okay.

+````````````````````````````````
+
+
+```````````````````````````````` example
+ 
+*foo*
+````````````````````````````````
+
+
+Here we have two HTML blocks with a Markdown paragraph between them:
+
+```````````````````````````````` example
+

+
+*Markdown*
+
+

+.
+

+
Markdown

+

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

+

+.
+

+

+````````````````````````````````
+
+
+```````````````````````````````` example
+

+

+.
+

+

+````````````````````````````````
+
+
+An open tag need not be closed:
+```````````````````````````````` example
+

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

+*foo*
+
bar

+````````````````````````````````
+
+
+
+A partial tag need not even be completed (garbage
+in, garbage out):
+
+```````````````````````````````` example
+
+.
+
+````````````````````````````````
+
+
+```````````````````````````````` example
+

+foo
+

+.
+

+foo
+

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

+``` c
+int x = 33;
+```
+.
+

+``` c
+int x = 33;
+```
+````````````````````````````````
+
+
+To start an [HTML block] with a tag that is *not* in the
+list of block-level tags in (6), you must put the tag by
+itself on the first line (and it must be complete):
+
+```````````````````````````````` example
+
+*bar*
+
+.
+
+*bar*
+
+````````````````````````````````
+
+
+In type 7 blocks, the [tag name] can be anything:
+
+```````````````````````````````` example
+
+*bar*
+
+.
+
+*bar*
+
+````````````````````````````````
+
+
+```````````````````````````````` example
+
+*bar*
+
+.
+
+*bar*
+
+````````````````````````````````
+
+
+```````````````````````````````` example
+
+*bar*
+.
+
+*bar*
+````````````````````````````````
+
+
+These rules are designed to allow us to work with tags that
+can function as either block-level or inline-level tags.
+The `` tag is a nice example.  We can surround content with
+`` tags in three different ways.  In this case, we get a raw
+HTML block, because the `` tag is on a line by itself:
+
+```````````````````````````````` example
+
+*foo*
+
+.
+
+*foo*
+
+````````````````````````````````
+
+
+In this case, we get a raw HTML block that just includes
+the `` tag (because it ends with the following blank
+line).  So the contents get interpreted as CommonMark:
+
+```````````````````````````````` example
+
+
+*foo*
+
+
+.
+
+
foo

+
+````````````````````````````````
+
+
+Finally, in this case, the `` tags are interpreted
+as [raw HTML] *inside* the CommonMark paragraph.  (Because
+the tag is not on a line by itself, we get inline HTML
+rather than an [HTML block].)
+
+```````````````````````````````` example
+*foo*
+.
+
foo

+````````````````````````````````
+
+
+HTML tags designed to contain literal content
+(`pre`, `script`, `style`, `textarea`), comments, processing instructions,
+and declarations are treated somewhat differently.
+Instead of ending at the first blank line, these blocks
+end at the first line containing a corresponding end tag.
+As a result, these blocks can contain blank lines:
+
+A pre tag (type 1):
+
+```````````````````````````````` example
+

+import Text.HTML.TagSoup
+
+main :: IO ()
+main = print $ parseTags tags
+

+okay
+.
+

+import Text.HTML.TagSoup
+
+main :: IO ()
+main = print $ parseTags tags
+

+
okay

+````````````````````````````````
+
+
+A script tag (type 1):
+
+```````````````````````````````` example
+
+okay
+.
+
+
okay

+````````````````````````````````
+
+
+A textarea tag (type 1):
+
+```````````````````````````````` example
+
+.
+
+````````````````````````````````
+
+A style tag (type 1):
+
+```````````````````````````````` example
+
+okay
+.
+
+
okay

+````````````````````````````````
+
+
+If there is no matching end tag, the block will end at the
+end of the document (or the enclosing [block quote][block quotes]
+or [list item][list items]):
+
+```````````````````````````````` example
+
+*foo*
+.
+
+
foo

+````````````````````````````````
+
+
+```````````````````````````````` example
+*bar*
+*baz*
+.
+*bar*
+
baz

+````````````````````````````````
+
+
+Note that anything on the last line after the
+end tag will be included in the [HTML block]:
+
+```````````````````````````````` example
+1. *bar*
+.
+1. *bar*
+````````````````````````````````
+
+
+A comment (type 2):
+
+```````````````````````````````` example
+
+okay
+.
+
+
okay

+````````````````````````````````
+
+
+
+A processing instruction (type 3):
+
+```````````````````````````````` example
+';
+
+?>
+okay
+.
+';
+
+?>
+
okay

+````````````````````````````````
+
+
+A declaration (type 4):
+
+```````````````````````````````` example
+
+.
+
+````````````````````````````````
+
+
+CDATA (type 5):
+
+```````````````````````````````` example
+
+okay
+.
+
+
okay

+````````````````````````````````
+
+
+The opening tag can be preceded by up to three spaces of indentation, but not
+four:
+
+```````````````````````````````` example
+  
+
+    
+.
+  
+
<!-- foo -->
+

+````````````````````````````````
+
+
+```````````````````````````````` example
+  

+
+    

+.
+  

+
<div>
+

+````````````````````````````````
+
+
+An HTML block of types 1--6 can interrupt a paragraph, and need not be
+preceded by a blank line.
+
+```````````````````````````````` example
+Foo
+

+bar
+

+.
+
Foo

+

+bar
+

+````````````````````````````````
+
+
+However, a following blank line is needed, except at the end of
+a document, and except for blocks of types 1--5, [above][HTML
+block]:
+
+```````````````````````````````` example
+

+bar
+

+*foo*
+.
+

+bar
+

+*foo*
+````````````````````````````````
+
+
+HTML blocks of type 7 cannot interrupt a paragraph:
+
+```````````````````````````````` example
+Foo
+
+baz
+.
+
Foo
+
+baz

+````````````````````````````````
+
+
+This rule differs from John Gruber's original Markdown syntax
+specification, which says:
+
+> 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 spaces or tabs.
+
+In some ways Gruber's rule is more restrictive than the one given
+here:
+
+- It requires that an HTML block be preceded by a blank line.
+- It does not allow the start tag to be indented.
+- It requires a matching end tag, which it also does not allow to
+  be indented.
+
+Most Markdown implementations (including some of Gruber's own) do not
+respect all of these restrictions.
+
+There is one respect, however, in which Gruber's rule is more liberal
+than the one given here, since it allows blank lines to occur inside
+an HTML block.  There are two reasons for disallowing them here.
+First, it removes the need to parse balanced tags, which is
+expensive and can require backtracking from the end of the document
+if no matching end tag is found. Second, it provides a very simple
+and flexible way of including Markdown content inside HTML tags:
+simply separate the Markdown from the HTML using blank lines:
+
+Compare:
+
+```````````````````````````````` example
+

+
+*Emphasized* text.
+
+

+.
+

+
Emphasized text.

+

+````````````````````````````````
+
+
+```````````````````````````````` example
+

+*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:
+
+```````````````````````````````` example
+

+
+
+
+
+
+
+
+

+Hi
+

+.
+
+
+
+
+

+Hi
+

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

+      Hi
+    

+.
+
+  
+
<td>
+  Hi
+</td>
+

+  
+

+````````````````````````````````
+
+
+Fortunately, blank lines are usually not necessary and can be
+deleted.  The exception is inside `
` tags, but as described
+[above][HTML blocks], raw HTML blocks starting with `
`
+*can* contain blank lines.
+
+## Link reference definitions
+
+A [link reference definition](@)
+consists of a [link label], optionally preceded by up to three spaces of
+indentation, followed
+by a colon (`:`), optional spaces or tabs (including up to one
+[line ending]), a [link destination],
+optional spaces or tabs (including up to one
+[line ending]), and an optional [link
+title], which if it is present must be separated
+from the [link destination] by spaces or tabs.
+No further character may occur.
+
+A [link reference definition]
+does not correspond to a structural element of a document.  Instead, it
+defines a label which can be used in [reference links]
+and reference-style [images] elsewhere in the document.  [Link
+reference definitions] can come either before or after the links that use
+them.
+
+```````````````````````````````` example
+[foo]: /url "title"
+
+[foo]
+.
+
foo

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

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

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

+````````````````````````````````
+
+
+The title may extend over multiple lines:
+
+```````````````````````````````` example
+[foo]: /url '
+title
+line1
+line2
+'
+
+[foo]
+.
+
foo

+````````````````````````````````
+
+
+However, it may not contain a [blank line]:
+
+```````````````````````````````` example
+[foo]: /url 'title
+
+with blank line'
+
+[foo]
+.
+
[foo]: /url 'title

+
with blank line'

+
[foo]

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

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

+
[foo]

+````````````````````````````````
+
+ However, an empty link destination may be specified using
+ angle brackets:
+
+```````````````````````````````` example
+[foo]: <>
+
+[foo]
+.
+
foo

+````````````````````````````````
+
+The title must be separated from the link destination by
+spaces or tabs:
+
+```````````````````````````````` example
+[foo]: (baz)
+
+[foo]
+.
+
[foo]: (baz)

+
[foo]

+````````````````````````````````
+
+
+Both title and destination can contain backslash escapes
+and literal backslashes:
+
+```````````````````````````````` example
+[foo]: /url\bar\*baz "foo\"bar\baz"
+
+[foo]
+.
+
foo

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

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

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

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

+````````````````````````````````
+
+
+Whether something is a [link reference definition] is
+independent of whether the link reference it defines is
+used in the document.  Thus, for example, the following
+document contains just a link reference definition, and
+no visible content:
+
+```````````````````````````````` example
+[foo]: /url
+.
+````````````````````````````````
+
+
+Here is another one:
+
+```````````````````````````````` example
+[
+foo
+]: /url
+bar
+.
+
bar

+````````````````````````````````
+
+
+This is not a link reference definition, because there are
+characters other than spaces or tabs after the title:
+
+```````````````````````````````` example
+[foo]: /url "title" ok
+.
+
[foo]: /url "title" ok

+````````````````````````````````
+
+
+This is a link reference definition, but it has no title:
+
+```````````````````````````````` example
+[foo]: /url
+"title" ok
+.
+
"title" ok

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

+
[foo]

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

+
[foo]

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

+
[bar]

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

+

+
bar

+

+````````````````````````````````
+
+```````````````````````````````` example
+[foo]: /url
+bar
+===
+[foo]
+.
+
bar

+
foo

+````````````````````````````````
+
+```````````````````````````````` example
+[foo]: /url
+===
+[foo]
+.
+
===
+foo

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

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

+

+

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

+
bbb

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

+
ccc
+ddd

+````````````````````````````````
+
+
+Multiple blank lines between paragraphs have no effect:
+
+```````````````````````````````` example
+aaa
+
+
+bbb
+.
+
aaa

+
bbb

+````````````````````````````````
+
+
+Leading spaces or tabs are skipped:
+
+```````````````````````````````` example
+  aaa
+ bbb
+.
+
aaa
+bbb

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+    aaa
+bbb
+.
+
aaa
+

+
bbb

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

+bbb

+````````````````````````````````
+
+
+## Blank lines
+
+[Blank lines] between block-level elements are ignored,
+except for the role they play in determining whether a [list]
+is [tight] or [loose].
+
+Blank lines at the beginning and end of the document are also ignored.
+
+```````````````````````````````` example
+  
+
+aaa
+  
+
+# aaa
+
+  
+.
+
aaa

+
aaa

+````````````````````````````````
+
+
+
+# Container blocks
+
+A [container block](#container-blocks) 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-parsing-strategy).)
+
+## Block quotes
+
+A [block quote marker](@),
+optionally preceded by up to three spaces of indentation,
+consists of (a) the character `>` together with a following space of
+indentation, or (b) a single character `>` not followed by a space of
+indentation.
+
+The following rules define [block quotes]:
+
+1.  **Basic case.**  If a string of lines *Ls* constitute a sequence
+    of blocks *Bs*, then the result of prepending a [block quote
+    marker] to the beginning of each line in *Ls*
+    is a [block quote](#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 character other than a space or tab after the
+    [block quote marker] is [paragraph continuation
+    text] is a block quote with *Bs* as its content.
+    [Paragraph continuation text](@) is text
+    that will be parsed as part of the content of a paragraph, but does
+    not occur at the beginning of the paragraph.
+
+3.  **Consecutiveness.**  A document cannot contain two [block
+    quotes] in a row unless there is a [blank line] between them.
+
+Nothing else counts as a [block quote](#block-quotes).
+
+Here is a simple example:
+
+```````````````````````````````` example
+> # Foo
+> bar
+> baz
+.
+

+
Foo

+
bar
+baz

+

+````````````````````````````````
+
+
+The space or tab after the `>` characters can be omitted:
+
+```````````````````````````````` example
+># Foo
+>bar
+> baz
+.
+

+
Foo

+
bar
+baz

+

+````````````````````````````````
+
+
+The `>` characters can be preceded by up to three spaces of indentation:
+
+```````````````````````````````` example
+   > # Foo
+   > bar
+ > baz
+.
+

+
Foo

+
bar
+baz

+

+````````````````````````````````
+
+
+Four spaces of indentation is too many:
+
+```````````````````````````````` example
+    > # Foo
+    > bar
+    > baz
+.
+
> # Foo
+> bar
+> baz
+

+````````````````````````````````
+
+
+The Laziness clause allows us to omit the `>` before
+[paragraph continuation text]:
+
+```````````````````````````````` example
+> # Foo
+> bar
+baz
+.
+

+
Foo

+
bar
+baz

+

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

+
bar
+baz
+foo

+

+````````````````````````````````
+
+
+Laziness only applies to lines that would have been continuations of
+paragraphs had they been prepended with [block quote markers].
+For example, the `> ` cannot be omitted in the second line of
+
+``` markdown
+> foo
+> ---
+```
+
+without changing the meaning:
+
+```````````````````````````````` example
+> foo
+---
+.
+

+
foo

+

+

+````````````````````````````````
+
+
+Similarly, if we omit the `> ` in the second line of
+
+``` markdown
+> - foo
+> - bar
+```
+
+then the block quote ends after the first line:
+
+```````````````````````````````` example
+> - foo
+- bar
+.
+

+
    
+
  • foo
    • 
+

+

+
    
+
  • bar
    • 
+

+````````````````````````````````
+
+
+For the same reason, we can't omit the `> ` in front of
+subsequent lines of an indented or fenced code block:
+
+```````````````````````````````` example
+>     foo
+    bar
+.
+

+
foo
+

+

+
bar
+

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

+

+

+
foo

+

+````````````````````````````````
+
+
+Note that in the following case, we have a [lazy
+continuation line]:
+
+```````````````````````````````` example
+> foo
+    - bar
+.
+

+
foo
+- bar

+

+````````````````````````````````
+
+
+To see why, note that in
+
+```markdown
+> foo
+>     - bar
+```
+
+the `- bar` is indented too far to start a list, and can't
+be an indented code block because indented code blocks cannot
+interrupt paragraphs, so it is [paragraph continuation text].
+
+A block quote can be empty:
+
+```````````````````````````````` example
+>
+.
+

+

+````````````````````````````````
+
+
+```````````````````````````````` example
+>
+>  
+> 
+.
+

+

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

+
foo

+

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

+
foo
+bar

+

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

+
foo

+
bar

+

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

+

+
bar

+

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

+
aaa

+

+

+

+
bbb

+

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

+
bar
+baz

+

+````````````````````````````````
+
+
+```````````````````````````````` example
+> bar
+
+baz
+.
+

+
bar

+

+
baz

+````````````````````````````````
+
+
+```````````````````````````````` example
+> 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:
+
+```````````````````````````````` example
+> > > foo
+bar
+.
+

+

+

+
foo
+bar

+

+

+

+````````````````````````````````
+
+
+```````````````````````````````` example
+>>> 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 of indentation.  So *five spaces* are needed
+after the `>`:
+
+```````````````````````````````` example
+>     code
+
+>    not code
+.
+

+
code
+

+

+

+
not code

+

+````````````````````````````````
+
+
+
+## List items
+
+A [list marker](@) is a
+[bullet list marker] or an [ordered list marker].
+
+A [bullet list marker](@)
+is a `-`, `+`, or `*` character.
+
+An [ordered list marker](@)
+is a sequence of 1--9 arabic digits (`0-9`), followed by either a
+`.` character or a `)` character.  (The reason for the length
+limit is that with 10 digits we start seeing integer overflows
+in some browsers.)
+
+The following rules define [list items]:
+
+1.  **Basic case.**  If a sequence of lines *Ls* constitute a sequence of
+    blocks *Bs* starting with a character other than a space or tab, and *M* is
+    a list marker of width *W* followed by 1 ≤ *N* ≤ 4 spaces of indentation,
+    then the result of prepending *M* and the following spaces to the first line
+    of Ls*, and indenting subsequent lines of *Ls* by *W + N* spaces, is a
+    list item with *Bs* as its contents.  The type of the list item
+    (bullet or ordered) is determined by the type of its list marker.
+    If the list item is ordered, then it is also assigned a start
+    number, based on the ordered list marker.
+
+    Exceptions:
+
+    1. When the first list item in a [list] interrupts
+       a paragraph---that is, when it starts on a line that would
+       otherwise count as [paragraph continuation text]---then (a)
+       the lines *Ls* must not begin with a blank line, and (b) if
+       the list item is ordered, the start number must be 1.
+    2. If any line is a [thematic break][thematic breaks] then
+       that line is not a list item.
+
+For example, let *Ls* be the lines
+
+```````````````````````````````` example
+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*:
+
+```````````````````````````````` example
+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 of indentation, and there are three spaces between
+the list marker and the next character other than a space or tab, then blocks
+must be indented five spaces in order to fall under the list
+item.
+
+Here are some examples showing how far content must be indented to be
+put under the list item:
+
+```````````````````````````````` example
+- one
+
+ two
+.
+
    
+
  • one
    • 
+

+
two

+````````````````````````````````
+
+
+```````````````````````````````` example
+- one
+
+  two
+.
+
    
+
  • 
+
    one
    
+
    two
    
+
    • 
+

+````````````````````````````````
+
+
+```````````````````````````````` example
+ -    one
+
+     two
+.
+
    
+
  • one
    • 
+

+
 two
+

+````````````````````````````````
+
+
+```````````````````````````````` example
+ -    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 character other than
+a space or tab after the list marker.  However, that is not quite right.
+The spaces of indentation after the list marker determine how much relative
+indentation is needed.  Which column this indentation reaches will depend on
+how the list item is embedded in other constructions, as shown by
+this example:
+
+```````````````````````````````` example
+   > > 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
+sufficient indentation after the last containing blockquote marker.
+
+The converse is also possible.  In the following example, the word `two`
+occurs far to the right of the initial text of the list item, `one`, but
+it is not considered part of the list item, because it is not indented
+far enough past the blockquote marker:
+
+```````````````````````````````` example
+>>- one
+>>
+  >  > two
+.
+

+

+
    
+
  • one
    • 
+

+
two

+

+

+````````````````````````````````
+
+
+Note that at least one space or tab is needed between the list marker and
+any following content, so these are not list items:
+
+```````````````````````````````` example
+-one
+
+2.two
+.
+
-one

+
2.two

+````````````````````````````````
+
+
+A list item may contain blocks that are separated by more than
+one blank line.
+
+```````````````````````````````` example
+- foo
+
+
+  bar
+.
+
    
+
  • 
+
    foo
    
+
    bar
    
+
    • 
+

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

+````````````````````````````````
+
+
+A list item that contains an indented code block will preserve
+empty lines within the code block verbatim.
+
+```````````````````````````````` example
+- Foo
+
+      bar
+
+
+      baz
+.
+
    
+
  • 
+
    Foo
    
+
    bar
+
+
+baz
+
    
+
    • 
+

+````````````````````````````````
+
+Note that ordered list start numbers must be nine digits or less:
+
+```````````````````````````````` example
+123456789. ok
+.
+
    
+
  1. ok
    2. 
+

+````````````````````````````````
+
+
+```````````````````````````````` example
+1234567890. not ok
+.
+
1234567890. not ok

+````````````````````````````````
+
+
+A start number may begin with 0s:
+
+```````````````````````````````` example
+0. ok
+.
+
    
+
  1. ok
    2. 
+

+````````````````````````````````
+
+
+```````````````````````````````` example
+003. ok
+.
+
    
+
  1. ok
    2. 
+

+````````````````````````````````
+
+
+A start number may not be negative:
+
+```````````````````````````````` example
+-1. not ok
+.
+
-1. not ok

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

+````````````````````````````````
+
+
+And in this case it is 11 spaces:
+
+```````````````````````````````` example
+  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 preceded by *one* space of indentation
+after the list marker:
+
+```````````````````````````````` example
+    indented code
+
+paragraph
+
+    more code
+.
+
indented code
+

+
paragraph

+
more code
+

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

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

+
bar

+````````````````````````````````
+
+
+```````````````````````````````` example
+-    foo
+
+  bar
+.
+
    
+
  • foo
    • 
+

+
bar

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

+````````````````````````````````
+
+
+3.  **Item starting with a blank line.**  If a sequence of lines *Ls*
+    starting with a single [blank line] constitute a (possibly empty)
+    sequence of blocks *Bs*, and *M* is a list marker of width *W*,
+    then the result of prepending *M* to the first line of *Ls*, and
+    preceding subsequent lines of *Ls* by *W + 1* spaces of indentation, is a
+    list item with *Bs* as its contents.
+    If a line is empty, then it need not be indented.  The type of the
+    list item (bullet or ordered) is determined by the type of its list
+    marker.  If the list item is ordered, then it is also assigned a
+    start number, based on the ordered list marker.
+
+Here are some list items that start with a blank line but are not empty:
+
+```````````````````````````````` example
+-
+  foo
+-
+  ```
+  bar
+  ```
+-
+      baz
+.
+
    
+
  • foo
    • 
+
  • 
+
    bar
+
    
+
    • 
+
  • 
+
    baz
+
    
+
    • 
+

+````````````````````````````````
+
+When the list item starts with a blank line, the number of spaces
+following the list marker doesn't change the required indentation:
+
+```````````````````````````````` example
+-   
+  foo
+.
+
    
+
  • foo
    • 
+

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

+
foo

+````````````````````````````````
+
+
+Here is an empty bullet list item:
+
+```````````````````````````````` example
+- foo
+-
+- bar
+.
+
    
+
  • foo
    • 
+
  • 
+
  • bar
    • 
+

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

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

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

+````````````````````````````````
+
+However, an empty list item cannot interrupt a paragraph:
+
+```````````````````````````````` example
+foo
+*
+
+foo
+1.
+.
+
foo
+*

+
foo
+1.

+````````````````````````````````
+
+
+4.  **Indentation.**  If a sequence of lines *Ls* constitutes a list item
+    according to rule #1, #2, or #3, then the result of preceding each line
+    of *Ls* by up to three spaces of indentation (the same for each line) also
+    constitutes a list item with the same contents and attributes.  If a line is
+    empty, then it need not be indented.
+
+Indented one space:
+
+```````````````````````````````` example
+ 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:
+
+```````````````````````````````` example
+  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:
+
+```````````````````````````````` example
+   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:
+
+```````````````````````````````` example
+    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 character other than a space or tab after the indentation is
+    [paragraph continuation text] is a
+    list item with the same contents and attributes.  The unindented
+    lines are called
+    [lazy continuation line](@)s.
+
+Here is an example with [lazy continuation lines]:
+
+```````````````````````````````` example
+  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:
+
+```````````````````````````````` example
+  1.  A paragraph
+    with two lines.
+.
+
    
+
  1. A paragraph
+with two lines.
    2. 
+

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

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

+

+````````````````````````````````
+
+
+```````````````````````````````` example
+> 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][List items].  A sublist must be indented the same number
+of spaces of indentation a paragraph would need to be in order to be included
+in the list item.
+
+So, in this case we need two spaces indent:
+
+```````````````````````````````` example
+- foo
+  - bar
+    - baz
+      - boo
+.
+
    
+
  • foo
+
      
+
    • bar
+
        
+
      • baz
+
          
+
        • boo
          • 
+
        
+
        • 
+
      
+
      • 
+
    
+
    • 
+

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

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

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

+
    
+
  • bar
    • 
+

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+1. - 2. foo
+.
+
    
+
  1. 
+
      
+
    • 
+
        
+
      1. foo
        2. 
+
      
+
      • 
+
    
+
    2. 
+

+````````````````````````````````
+
+
+A list item can contain a heading:
+
+```````````````````````````````` example
+- # 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 up to three spaces of indentation for
+the initial list marker, allows text that is indented *less than* the
+original list marker to be included in the list item. For example,
+`Markdown.pl` parses
+
+``` 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](@) is a sequence of one or more
+list items [of the same type].  The list items
+may be separated by any number of blank lines.
+
+Two list items are [of the same type](@)
+if they begin with a [list marker] of the same type.
+Two list markers are of the
+same type if (a) they are bullet list markers using the same character
+(`-`, `+`, or `*`) or (b) they are ordered list numbers with the same
+delimiter (either `.` or `)`).
+
+A list is an [ordered list](@)
+if its constituent list items begin with
+[ordered list markers], and a
+[bullet list](@) if its constituent list
+items begin with [bullet list markers].
+
+The [start number](@)
+of an [ordered list] is determined by the list number of
+its initial list item.  The numbers of subsequent list items are
+disregarded.
+
+A list is [loose](@) if any of its constituent
+list items are separated by blank lines, or if any of its constituent
+list items directly contain two block-level elements with a blank line
+between them.  Otherwise a list is [tight](@).
+(The difference in HTML output is that paragraphs in a loose list are
+wrapped in `
` tags, while paragraphs in a tight list are not.)
+
+Changing the bullet or ordered list delimiter starts a new list:
+
+```````````````````````````````` example
+- foo
+- bar
++ baz
+.
+
    
+
  • foo
    • 
+
  • bar
    • 
+

+
    
+
  • baz
    • 
+

+````````````````````````````````
+
+
+```````````````````````````````` example
+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:
+
+```````````````````````````````` example
+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:
+
+``` markdown
+The number of windows in my house is
+14.  The number of doors is 6.
+```
+
+Oddly, though, `Markdown.pl` *does* allow a blockquote to
+interrupt a paragraph, even though the same considerations might
+apply.
+
+In CommonMark, we do allow lists to interrupt paragraphs, for
+two reasons.  First, it is natural and not uncommon for people
+to start lists without blank lines:
+
+``` markdown
+I need to buy
+- new shoes
+- a coat
+- a plane ticket
+```
+
+Second, we are attracted to a
+
+> [principle of uniformity](@):
+> if a chunk of text has a certain
+> meaning, it will continue to have the same meaning when put into a
+> container block (such as a list item or blockquote).
+
+(Indeed, the spec for [list items] and [block quotes] presupposes
+this principle.) This principle implies that if
+
+``` markdown
+  * 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
+
+``` markdown
+I need to buy
+- new shoes
+- a coat
+- a plane ticket
+```
+
+by itself should be a paragraph followed by a nested sublist.
+
+Since it is well established Markdown practice to allow lists to
+interrupt paragraphs inside list items, the [principle of
+uniformity] requires us to allow this outside list items as
+well.  ([reStructuredText](http://docutils.sourceforge.net/rst.html)
+takes a different approach, requiring blank lines before lists
+even inside other list items.)
+
+In order to solve of unwanted lists in paragraphs with
+hard-wrapped numerals, we allow only lists starting with `1` to
+interrupt paragraphs.  Thus,
+
+```````````````````````````````` example
+The number of windows in my house is
+14.  The number of doors is 6.
+.
+
The number of windows in my house is
+14.  The number of doors is 6.

+````````````````````````````````
+
+We may still get an unintended result in cases like
+
+```````````````````````````````` example
+The number of windows in my house is
+1.  The number of doors is 6.
+.
+
The number of windows in my house is

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

+````````````````````````````````
+
+but this rule should prevent most spurious list captures.
+
+There can be any number of blank lines between items:
+
+```````````````````````````````` example
+- foo
+
+- bar
+
+
+- baz
+.
+
    
+
  • 
+
    foo
    
+
    • 
+
  • 
+
    bar
    
+
    • 
+
  • 
+
    baz
    
+
    • 
+

+````````````````````````````````
+
+```````````````````````````````` example
+- foo
+  - bar
+    - baz
+
+
+      bim
+.
+
    
+
  • foo
+
      
+
    • bar
+
        
+
      • 
+
        baz
        
+
        bim
        
+
        • 
+
      
+
      • 
+
    
+
    • 
+

+````````````````````````````````
+
+
+To separate consecutive lists of the same type, or to separate a
+list from an indented code block that would otherwise be parsed
+as a subparagraph of the final list item, you can insert a blank HTML
+comment:
+
+```````````````````````````````` example
+- foo
+- bar
+
+
+
+- baz
+- bim
+.
+
    
+
  • foo
    • 
+
  • bar
    • 
+

+
+
    
+
  • baz
    • 
+
  • bim
    • 
+

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+1. a
+
+  2. b
+
+   3. c
+.
+
    
+
  1. 
+
    a
    
+
    2. 
+
  2. 
+
    b
    
+
    3. 
+
  3. 
+
    c
    
+
    4. 
+

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

+````````````````````````````````
+
+And here, `3. c` is treated as in indented code block,
+because it is indented four spaces and preceded by a
+blank line.
+
+```````````````````````````````` example
+1. a
+
+  2. b
+
+    3. c
+.
+
    
+
  1. 
+
    a
    
+
    2. 
+
  2. 
+
    b
    
+
    3. 
+

+
3. c
+

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

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

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

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

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

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

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+- a
+  - b
+.
+
    
+
  • a
+
      
+
    • b
      • 
+
    
+
    • 
+

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+- 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
+
+```````````````````````````````` example
+`hi`lo`
+.
+
hilo`

+````````````````````````````````
+
+`hi` is parsed as code, leaving the backtick at the end as a literal
+backtick.
+
+
+
+## Code spans
+
+A [backtick string](@)
+is a string of one or more backtick characters (`` ` ``) that is neither
+preceded nor followed by a backtick.
+
+A [code span](@) begins with a backtick string and ends with
+a backtick string of equal length.  The contents of the code span are
+the characters between these two backtick strings, normalized in the
+following ways:
+
+- First, [line endings] are converted to [spaces].
+- If the resulting string both begins *and* ends with a [space]
+  character, but does not consist entirely of [space]
+  characters, a single [space] character is removed from the
+  front and back.  This allows you to include code that begins
+  or ends with backtick characters, which must be separated by
+  whitespace from the opening or closing backtick strings.
+
+This is a simple code span:
+
+```````````````````````````````` example
+`foo`
+.
+
foo

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

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

+````````````````````````````````
+
+Note that only *one* space is stripped:
+
+```````````````````````````````` example
+`  ``  `
+.
+
 `` 

+````````````````````````````````
+
+The stripping only happens if the space is on both
+sides of the string:
+
+```````````````````````````````` example
+` a`
+.
+
 a

+````````````````````````````````
+
+Only [spaces], and not [unicode whitespace] in general, are
+stripped in this way:
+
+```````````````````````````````` example
+` b `
+.
+
 b 

+````````````````````````````````
+
+No stripping occurs if the code span contains only spaces:
+
+```````````````````````````````` example
+` `
+`  `
+.
+
 
+  

+````````````````````````````````
+
+
+[Line endings] are treated like spaces:
+
+```````````````````````````````` example
+``
+foo
+bar  
+baz
+``
+.
+
foo bar   baz

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

+````````````````````````````````
+
+
+Interior spaces are not collapsed:
+
+```````````````````````````````` example
+`foo   bar 
+baz`
+.
+
foo   bar  baz

+````````````````````````````````
+
+Note that browsers will typically collapse consecutive spaces
+when rendering `` elements, so it is recommended that
+the following CSS be used:
+
+    code{white-space: pre-wrap;}
+
+
+Note that backslash escapes do not work in code spans. All backslashes
+are treated literally:
+
+```````````````````````````````` example
+`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.
+
+```````````````````````````````` example
+``foo`bar``
+.
+
foo`bar

+````````````````````````````````
+
+```````````````````````````````` example
+` foo `` bar `
+.
+
foo `` bar

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

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

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

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

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

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

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

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

+````````````````````````````````
+
+The following case also illustrates the need for opening and
+closing backtick strings to be equal in length:
+
+```````````````````````````````` example
+`foo``bar``
+.
+
`foobar

+````````````````````````````````
+
+
+## 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](@) is either
+a sequence of one or more `*` characters that is not preceded or
+followed by a non-backslash-escaped `*` character, or a sequence
+of one or more `_` characters that is not preceded or followed by
+a non-backslash-escaped `_` character.
+
+A [left-flanking delimiter run](@) is
+a [delimiter run] that is (1) not followed by [Unicode whitespace],
+and either (2a) not followed by a [Unicode punctuation character], or
+(2b) followed by a [Unicode punctuation character] and
+preceded by [Unicode whitespace] or a [Unicode punctuation character].
+For purposes of this definition, the beginning and the end of
+the line count as Unicode whitespace.
+
+A [right-flanking delimiter run](@) is
+a [delimiter run] that is (1) not preceded by [Unicode whitespace],
+and either (2a) not preceded by a [Unicode punctuation character], or
+(2b) preceded by a [Unicode punctuation character] and
+followed by [Unicode whitespace] or a [Unicode punctuation character].
+For purposes of this definition, the beginning and the end of
+the line count as Unicode whitespace.
+
+Here are some examples of delimiter runs.
+
+  - left-flanking but not right-flanking:
+
+    ```
+    ***abc
+      _abc
+    **"abc"
+     _"abc"
+    ```
+
+  - right-flanking but not left-flanking:
+
+    ```
+     abc***
+     abc_
+    "abc"**
+    "abc"_
+    ```
+
+  - Both left and right-flanking:
+
+    ```
+     abc***def
+    "abc"_"def"
+    ```
+
+  - Neither left nor right-flanking:
+
+    ```
+    abc *** def
+    a _ b
+    ```
+
+(The idea of distinguishing left-flanking and right-flanking
+delimiter runs based on the character before and the character
+after comes from Roopesh Chander's
+[vfmd](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](@)
+    iff (if and only if) it is part of a [left-flanking delimiter run].
+
+2.  A single `_` character [can open emphasis] iff
+    it is part of a [left-flanking delimiter run]
+    and either (a) not part of a [right-flanking delimiter run]
+    or (b) part of a [right-flanking delimiter run]
+    preceded by a [Unicode punctuation character].
+
+3.  A single `*` character [can close emphasis](@)
+    iff it is part of a [right-flanking delimiter run].
+
+4.  A single `_` character [can close emphasis] iff
+    it is part of a [right-flanking delimiter run]
+    and either (a) not part of a [left-flanking delimiter run]
+    or (b) part of a [left-flanking delimiter run]
+    followed by a [Unicode punctuation character].
+
+5.  A double `**` [can open strong emphasis](@)
+    iff it is part of a [left-flanking delimiter run].
+
+6.  A double `__` [can open strong emphasis] iff
+    it is part of a [left-flanking delimiter run]
+    and either (a) not part of a [right-flanking delimiter run]
+    or (b) part of a [right-flanking delimiter run]
+    preceded by a [Unicode punctuation character].
+
+7.  A double `**` [can close strong emphasis](@)
+    iff it is part of a [right-flanking delimiter run].
+
+8.  A double `__` [can close strong emphasis] iff
+    it is part of a [right-flanking delimiter run]
+    and either (a) not part of a [left-flanking delimiter run]
+    or (b) part of a [left-flanking delimiter run]
+    followed by a [Unicode punctuation character].
+
+9.  Emphasis begins with a delimiter that [can open emphasis] and ends
+    with a delimiter that [can close emphasis], and that uses the same
+    character (`_` or `*`) as the opening delimiter.  The
+    opening and closing delimiters must belong to separate
+    [delimiter runs].  If one of the delimiters can both
+    open and close emphasis, then the sum of the lengths of the
+    delimiter runs containing the opening and closing delimiters
+    must not be a multiple of 3 unless both lengths are
+    multiples of 3.
+
+10. Strong emphasis begins with a delimiter that
+    [can open strong emphasis] and ends with a delimiter that
+    [can close strong emphasis], and that uses the same character
+    (`_` or `*`) as the opening delimiter.  The
+    opening and closing delimiters must belong to separate
+    [delimiter runs].  If one of the delimiters can both open
+    and close strong emphasis, then the sum of the lengths of
+    the delimiter runs containing the opening and closing
+    delimiters must not be a multiple of 3 unless both lengths
+    are multiples of 3.
+
+11. A literal `*` character cannot occur at the beginning or end of
+    `*`-delimited emphasis or `**`-delimited strong emphasis, unless it
+    is backslash-escaped.
+
+12. A literal `_` character cannot occur at the beginning or end of
+    `_`-delimited emphasis or `__`-delimited strong emphasis, unless it
+    is backslash-escaped.
+
+Where rules 1--12 above are compatible with multiple parsings,
+the following principles resolve ambiguity:
+
+13. The number of nestings should be minimized. Thus, for example,
+    an interpretation `...` 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`.
+
+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:
+
+```````````````````````````````` example
+*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]:
+
+```````````````````````````````` example
+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]:
+
+```````````````````````````````` example
+a*"foo"*
+.
+
a*"foo"*

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+5*6*78
+.
+
5678

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

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

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+5_6_78
+.
+
5_6_78

+````````````````````````````````
+
+
+```````````````````````````````` example
+пристаням_стремятся_
+.
+
пристаням_стремятся_

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

+````````````````````````````````
+
+
+This is emphasis, even though the opening delimiter is
+both left- and right-flanking, because it is preceded by
+punctuation:
+
+```````````````````````````````` example
+foo-_(bar)_
+.
+
foo-(bar)

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

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

+````````````````````````````````
+
+
+A line ending also counts as whitespace:
+
+```````````````````````````````` example
+*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]:
+
+```````````````````````````````` example
+*(*foo)
+.
+
*(*foo)

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

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

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

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

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+_пристаням_стремятся
+.
+
_пристаням_стремятся

+````````````````````````````````
+
+
+```````````````````````````````` example
+_foo_bar_baz_
+.
+
foo_bar_baz

+````````````````````````````````
+
+
+This is emphasis, even though the closing delimiter is
+both left- and right-flanking, because it is followed by
+punctuation:
+
+```````````````````````````````` example
+_(bar)_.
+.
+
(bar).

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

+````````````````````````````````
+
+
+This is not strong emphasis, because the opening delimiter is
+followed by whitespace:
+
+```````````````````````````````` example
+** 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]:
+
+```````````````````````````````` example
+a**"foo"**
+.
+
a**"foo"**

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

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

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

+````````````````````````````````
+
+
+A line ending counts as whitespace:
+```````````````````````````````` example
+__
+foo bar__
+.
+
__
+foo bar__

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+5__6__78
+.
+
5__6__78

+````````````````````````````````
+
+
+```````````````````````````````` example
+пристаням__стремятся__
+.
+
пристаням__стремятся__

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

+````````````````````````````````
+
+
+This is strong emphasis, even though the opening delimiter is
+both left- and right-flanking, because it is preceded by
+punctuation:
+
+```````````````````````````````` example
+foo-__(bar)__
+.
+
foo-(bar)

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

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+**foo "*bar*" foo**
+.
+
foo "bar" foo

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

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

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

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+__пристаням__стремятся
+.
+
__пристаням__стремятся

+````````````````````````````````
+
+
+```````````````````````````````` example
+__foo__bar__baz__
+.
+
foo__bar__baz

+````````````````````````````````
+
+
+This is strong emphasis, even though the closing delimiter is
+both left- and right-flanking, because it is followed by
+punctuation:
+
+```````````````````````````````` example
+__(bar)__.
+.
+
(bar).

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+*foo
+bar*
+.
+
foo
+bar

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+__foo_ bar_
+.
+
foo bar

+````````````````````````````````
+
+
+```````````````````````````````` example
+*foo *bar**
+.
+
foo bar

+````````````````````````````````
+
+
+```````````````````````````````` example
+*foo **bar** baz*
+.
+
foo bar baz

+````````````````````````````````
+
+```````````````````````````````` example
+*foo**bar**baz*
+.
+
foobarbaz

+````````````````````````````````
+
+Note that in the preceding case, the interpretation
+
+``` markdown
+
foobarbaz

+```
+
+
+is precluded by the condition that a delimiter that
+can both open and close (like the `*` after `foo`)
+cannot form emphasis if the sum of the lengths of
+the delimiter runs containing the opening and
+closing delimiters is a multiple of 3 unless
+both lengths are multiples of 3.
+
+
+For the same reason, we don't get two consecutive
+emphasis sections in this example:
+
+```````````````````````````````` example
+*foo**bar*
+.
+
foo**bar

+````````````````````````````````
+
+
+The same condition ensures that the following
+cases are all strong emphasis nested inside
+emphasis, even when the interior whitespace is
+omitted:
+
+
+```````````````````````````````` example
+***foo** bar*
+.
+
foo bar

+````````````````````````````````
+
+
+```````````````````````````````` example
+*foo **bar***
+.
+
foo bar

+````````````````````````````````
+
+
+```````````````````````````````` example
+*foo**bar***
+.
+
foobar

+````````````````````````````````
+
+
+When the lengths of the interior closing and opening
+delimiter runs are *both* multiples of 3, though,
+they can match to create emphasis:
+
+```````````````````````````````` example
+foo***bar***baz
+.
+
foobarbaz

+````````````````````````````````
+
+```````````````````````````````` example
+foo******bar*********baz
+.
+
foobar***baz

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

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

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+**foo
+bar**
+.
+
foo
+bar

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+____foo__ bar__
+.
+
foo bar

+````````````````````````````````
+
+
+```````````````````````````````` example
+**foo **bar****
+.
+
foo bar

+````````````````````````````````
+
+
+```````````````````````````````` example
+**foo *bar* baz**
+.
+
foo bar baz

+````````````````````````````````
+
+
+```````````````````````````````` example
+**foo*bar*baz**
+.
+
foobarbaz

+````````````````````````````````
+
+
+```````````````````````````````` example
+***foo* bar**
+.
+
foo bar

+````````````````````````````````
+
+
+```````````````````````````````` example
+**foo *bar***
+.
+
foo bar

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

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

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

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

+````````````````````````````````
+
+
+
+Rule 11:
+
+```````````````````````````````` example
+foo ***
+.
+
foo ***

+````````````````````````````````
+
+
+```````````````````````````````` example
+foo *\**
+.
+
foo *

+````````````````````````````````
+
+
+```````````````````````````````` example
+foo *_*
+.
+
foo _

+````````````````````````````````
+
+
+```````````````````````````````` example
+foo *****
+.
+
foo *****

+````````````````````````````````
+
+
+```````````````````````````````` example
+foo **\***
+.
+
foo *

+````````````````````````````````
+
+
+```````````````````````````````` example
+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:
+
+```````````````````````````````` example
+**foo*
+.
+
*foo

+````````````````````````````````
+
+
+```````````````````````````````` example
+*foo**
+.
+
foo*

+````````````````````````````````
+
+
+```````````````````````````````` example
+***foo**
+.
+
*foo

+````````````````````````````````
+
+
+```````````````````````````````` example
+****foo*
+.
+
***foo

+````````````````````````````````
+
+
+```````````````````````````````` example
+**foo***
+.
+
foo*

+````````````````````````````````
+
+
+```````````````````````````````` example
+*foo****
+.
+
foo***

+````````````````````````````````
+
+
+
+Rule 12:
+
+```````````````````````````````` example
+foo ___
+.
+
foo ___

+````````````````````````````````
+
+
+```````````````````````````````` example
+foo _\__
+.
+
foo _

+````````````````````````````````
+
+
+```````````````````````````````` example
+foo _*_
+.
+
foo *

+````````````````````````````````
+
+
+```````````````````````````````` example
+foo _____
+.
+
foo _____

+````````````````````````````````
+
+
+```````````````````````````````` example
+foo __\___
+.
+
foo _

+````````````````````````````````
+
+
+```````````````````````````````` example
+foo __*__
+.
+
foo *

+````````````````````````````````
+
+
+```````````````````````````````` example
+__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:
+
+```````````````````````````````` example
+_foo__
+.
+
foo_

+````````````````````````````````
+
+
+```````````````````````````````` example
+___foo__
+.
+
_foo

+````````````````````````````````
+
+
+```````````````````````````````` example
+____foo_
+.
+
___foo

+````````````````````````````````
+
+
+```````````````````````````````` example
+__foo___
+.
+
foo_

+````````````````````````````````
+
+
+```````````````````````````````` example
+_foo____
+.
+
foo___

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+*_foo_*
+.
+
foo

+````````````````````````````````
+
+
+```````````````````````````````` example
+__foo__
+.
+
foo

+````````````````````````````````
+
+
+```````````````````````````````` example
+_*foo*_
+.
+
foo

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+____foo____
+.
+
foo

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

+````````````````````````````````
+
+
+Rule 14:
+
+```````````````````````````````` example
+***foo***
+.
+
foo

+````````````````````````````````
+
+
+```````````````````````````````` example
+_____foo_____
+.
+
foo

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+*foo __bar *baz bim__ bam*
+.
+
foo bar *baz bim bam

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+*foo *bar baz*
+.
+
*foo bar baz

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+*
+.
+
*

+````````````````````````````````
+
+
+```````````````````````````````` example
+**
+.
+
**

+````````````````````````````````
+
+
+```````````````````````````````` example
+__
+.
+
__

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

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+__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 links] the
+destination and title are given immediately after the link text.  In
+[reference links] the destination and title are defined elsewhere in
+the document.
+
+A [link text](@) consists of a sequence of zero or more
+inline elements enclosed by square brackets (`[` and `]`).  The
+following rules apply:
+
+- Links may not contain other links, at any level of nesting. If
+  multiple otherwise valid link definitions appear nested inside each
+  other, the inner-most definition is used.
+
+- Brackets are allowed in the [link text] only if (a) they
+  are backslash-escaped or (b) they appear as a matched pair of brackets,
+  with an open bracket `[`, a sequence of zero or more inlines, and
+  a close bracket `]`.
+
+- Backtick [code spans], [autolinks], and raw [HTML tags] bind more tightly
+  than the brackets in link text.  Thus, for example,
+  `` [foo`]` `` could not be a link text, since the second `]`
+  is part of a code span.
+
+- The brackets in link text bind more tightly than markers for
+  [emphasis and strong emphasis]. Thus, for example, `*[foo*](url)` is a link.
+
+A [link destination](@) consists of either
+
+- a sequence of zero or more characters between an opening `<` and a
+  closing `>` that contains no line endings or unescaped
+  `<` or `>` characters, or
+
+- a nonempty sequence of characters that does not start with `<`,
+  does not include [ASCII control characters][ASCII control character]
+  or [space] character, and includes parentheses only if (a) they are
+  backslash-escaped or (b) they are part of a balanced pair of
+  unescaped parentheses.
+  (Implementations may impose limits on parentheses nesting to
+  avoid performance issues, but at least three levels of nesting
+  should be supported.)
+
+A [link title](@)  consists of either
+
+- a sequence of zero or more characters between straight double-quote
+  characters (`"`), including a `"` character only if it is
+  backslash-escaped, or
+
+- a sequence of zero or more characters between straight single-quote
+  characters (`'`), including a `'` character only if it is
+  backslash-escaped, or
+
+- a sequence of zero or more characters between matching parentheses
+  (`(...)`), including a `(` or `)` character only if it is
+  backslash-escaped.
+
+Although [link titles] may span multiple lines, they may not contain
+a [blank line].
+
+An [inline link](@) consists of a [link text] followed immediately
+by a left parenthesis `(`, an optional [link destination], an optional
+[link title], and a right parenthesis `)`.
+These four components may be separated by spaces, tabs, and up to one line
+ending.
+If both [link destination] and [link title] are present, they *must* be
+separated by spaces, tabs, and up to one line ending.
+
+The link's text consists of the inlines contained
+in the [link text] (excluding the enclosing square brackets).
+The link's URI consists of the link destination, excluding enclosing
+`<...>` if present, with backslash-escapes in effect as described
+above.  The link's title consists of the link title, excluding its
+enclosing delimiters, with backslash-escapes in effect as described
+above.
+
+Here is a simple inline link:
+
+```````````````````````````````` example
+[link](/uri "title")
+.
+
link

+````````````````````````````````
+
+
+The title, the link text and even 
+the destination may be omitted:
+
+```````````````````````````````` example
+[link](/uri)
+.
+
link

+````````````````````````````````
+
+```````````````````````````````` example
+[](./target.md)
+.
+

+````````````````````````````````
+
+
+```````````````````````````````` example
+[link]()
+.
+
link

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+[]()
+.
+

+````````````````````````````````
+
+The destination can only contain spaces if it is
+enclosed in pointy brackets:
+
+```````````````````````````````` example
+[link](/my uri)
+.
+
[link](/my uri)

+````````````````````````````````
+
+```````````````````````````````` example
+[link]()
+.
+
link

+````````````````````````````````
+
+The destination cannot contain line endings,
+even if enclosed in pointy brackets:
+
+```````````````````````````````` example
+[link](foo
+bar)
+.
+
[link](foo
+bar)

+````````````````````````````````
+
+```````````````````````````````` example
+[link]()
+.
+
[link]()

+````````````````````````````````
+
+The destination can contain `)` if it is enclosed
+in pointy brackets:
+
+```````````````````````````````` example
+[a]()
+.
+
a

+````````````````````````````````
+
+Pointy brackets that enclose links must be unescaped:
+
+```````````````````````````````` example
+[link]()
+.
+
[link](<foo>)

+````````````````````````````````
+
+These are not links, because the opening pointy bracket
+is not matched properly:
+
+```````````````````````````````` example
+[a](
+[a](c)
+.
+
[a](<b)c
+[a](<b)c>
+[a](c)

+````````````````````````````````
+
+Parentheses inside the link destination may be escaped:
+
+```````````````````````````````` example
+[link](\(foo\))
+.
+
link

+````````````````````````````````
+
+Any number of parentheses are allowed without escaping, as long as they are
+balanced:
+
+```````````````````````````````` example
+[link](foo(and(bar)))
+.
+
link

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+[link]()
+.
+
link

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

+````````````````````````````````
+
+
+A link can contain fragment identifiers and queries:
+
+```````````````````````````````` example
+[link](#fragment)
+
+[link](http://example.com#fragment)
+
+[link](http://example.com?foo=3#frag)
+.
+
link

+
link

+
link

+````````````````````````````````
+
+
+Note that a backslash before a non-escapable character is
+just a backslash:
+
+```````````````````````````````` example
+[link](foo\bar)
+.
+
link

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

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

+````````````````````````````````
+
+
+Backslash escapes and entity and numeric character references
+may be used in titles:
+
+```````````````````````````````` example
+[link](/url "title \""")
+.
+
link

+````````````````````````````````
+
+
+Titles must be separated from the link using spaces, tabs, and up to one line
+ending.
+Other [Unicode whitespace] like non-breaking space doesn't work.
+
+```````````````````````````````` example
+[link](/url "title")
+.
+
link

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

+````````````````````````````````
+
+
+But it is easy to work around this by using a different quote type:
+
+```````````````````````````````` example
+[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,
+entity and numeric character references, or using a different
+quote type for the enclosing title---to write titles containing
+double quotes.  `Markdown.pl`'s handling of titles has a number
+of other strange features.  For example, it allows single-quoted
+titles in inline links, but not reference links.  And, in
+reference links but not inline links, it allows a title to begin
+with `"` and end with `)`.  `Markdown.pl` 1.0.1 even allows
+titles with no closing quotation mark, though 1.0.2b8 does not.
+It seems preferable to adopt a simple, rational rule that works
+the same way in inline links and link reference definitions.)
+
+Spaces, tabs, and up to one line ending is allowed around the destination and
+title:
+
+```````````````````````````````` example
+[link](   /uri
+  "title"  )
+.
+
link

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

+````````````````````````````````
+
+
+There are three kinds of [reference link](@)s:
+[full](#full-reference-link), [collapsed](#collapsed-reference-link),
+and [shortcut](#shortcut-reference-link).
+
+A [full reference link](@)
+consists of a [link text] immediately followed by a [link label]
+that [matches] a [link reference definition] elsewhere in the document.
+
+A [link label](@)  begins with a left bracket (`[`) and ends
+with the first right bracket (`]`) that is not backslash-escaped.
+Between these brackets there must be at least one character that is not a space,
+tab, or line ending.
+Unescaped square bracket characters are not allowed inside the
+opening and closing square brackets of [link labels].  A link
+label can have at most 999 characters inside the square
+brackets.
+
+One label [matches](@)
+another just in case their normalized forms are equal.  To normalize a
+label, strip off the opening and closing brackets,
+perform the *Unicode case fold*, strip leading and trailing
+spaces, tabs, and line endings, and collapse consecutive internal
+spaces, tabs, and line endings to a single space.  If there are multiple
+matching reference link definitions, the one that comes first in the
+document is used.  (It is desirable in such cases to emit a warning.)
+
+The link's URI and title are provided by the matching [link
+reference definition].
+
+Here is a simple example:
+
+```````````````````````````````` example
+[foo][bar]
+
+[bar]: /url "title"
+.
+
foo

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

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

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

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

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

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

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

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

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

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

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

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

+````````````````````````````````
+
+
+Unicode case fold is used:
+
+```````````````````````````````` example
+[ẞ]
+
+[SS]: /url
+.
+
ẞ

+````````````````````````````````
+
+
+Consecutive internal spaces, tabs, and line endings are treated as one space for
+purposes of determining matching:
+
+```````````````````````````````` example
+[Foo
+  bar]: /url
+
+[Baz][Foo bar]
+.
+
Baz

+````````````````````````````````
+
+
+No spaces, tabs, or line endings are allowed between the [link text] and the
+[link label]:
+
+```````````````````````````````` example
+[foo] [bar]
+
+[bar]: /url "title"
+.
+
[foo] bar

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

+````````````````````````````````
+
+
+This is a departure from John Gruber's original Markdown syntax
+description, which explicitly allows whitespace between the link
+text and the link label.  It brings reference links in line with
+[inline links], which (according to both original Markdown and
+this spec) cannot have whitespace after the link text.  More
+importantly, it prevents inadvertent capture of consecutive
+[shortcut reference links]. If whitespace is allowed between the
+link text and the link label, then in the following we will have
+a single reference link, not two shortcut reference links, as
+intended:
+
+``` markdown
+[foo]
+[bar]
+
+[foo]: /url1
+[bar]: /url2
+```
+
+(Note that [shortcut reference links] were introduced by Gruber
+himself in a beta version of `Markdown.pl`, but never included
+in the official syntax description.  Without shortcut reference
+links, it is harmless to allow space between the link text and
+link label; but once shortcut references are introduced, it is
+too dangerous to allow this, as it frequently leads to
+unintended results.)
+
+When there are multiple matching [link reference definitions],
+the first is used:
+
+```````````````````````````````` example
+[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:
+
+```````````````````````````````` example
+[bar][foo\!]
+
+[foo!]: /url
+.
+
[bar][foo!]

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

+
[ref[]: /uri

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

+
[ref[bar]]: /uri

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

+
[[[foo]]]: /url

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

+````````````````````````````````
+
+
+Note that in this example `]` is not backslash-escaped:
+
+```````````````````````````````` example
+[bar\\]: /uri
+
+[bar\\]
+.
+
bar\

+````````````````````````````````
+
+
+A [link label] must contain at least one character that is not a space, tab, or
+line ending:
+
+```````````````````````````````` example
+[]
+
+[]: /uri
+.
+
[]

+
[]: /uri

+````````````````````````````````
+
+
+```````````````````````````````` example
+[
+ ]
+
+[
+ ]: /uri
+.
+
[
+]

+
[
+]: /uri

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

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

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

+````````````````````````````````
+
+
+
+As with full reference links, spaces, tabs, or line endings are not
+allowed between the two sets of brackets:
+
+```````````````````````````````` example
+[foo] 
+[]
+
+[foo]: /url "title"
+.
+
foo
+[]

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

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+[[bar [foo]
+
+[foo]: /url
+.
+
[[bar foo

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

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

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

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

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

+````````````````````````````````
+
+```````````````````````````````` example
+[foo][]
+
+[foo]: /url1
+.
+
foo

+````````````````````````````````
+
+Inline links also take precedence:
+
+```````````````````````````````` example
+[foo]()
+
+[foo]: /url1
+.
+
foo

+````````````````````````````````
+
+```````````````````````````````` example
+[foo](not a link)
+
+[foo]: /url1
+.
+
foo(not a link)

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

+````````````````````````````````
+
+
+Here, though, `[foo][bar]` is parsed as a reference, since
+`[bar]` is defined:
+
+```````````````````````````````` example
+[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):
+
+```````````````````````````````` example
+[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](@).  The rules for this are the
+same as for [link text], except that (a) an
+image description starts with `![` rather than `[`, and
+(b) an image description may contain links.
+An image description has inline elements
+as its contents.  When an image is rendered to HTML,
+this is standardly used as the image's `alt` attribute.
+
+```````````````````````````````` example
+![foo](/url "title")
+.
+
foo

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

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

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

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

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

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

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

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

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

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

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

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

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

+````````````````````````````````
+
+
+As with reference links, spaces, tabs, and line endings, are not allowed
+between the two sets of brackets:
+
+```````````````````````````````` example
+![foo] 
+[]
+
+[foo]: /url "title"
+.
+
foo
+[]

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

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

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

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

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

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

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

+````````````````````````````````
+
+
+## Autolinks
+
+[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](@) consists of `<`, followed by an
+[absolute URI] followed by `>`.  It is parsed as
+a link to the URI, with the URI as the link's label.
+
+An [absolute URI](@),
+for these purposes, consists of a [scheme] followed by a colon (`:`)
+followed by zero or more characters other [ASCII control
+characters][ASCII control character], [space], `<`, and `>`.
+If the URI includes these characters, they must be percent-encoded
+(e.g. `%20` for a space).
+
+For purposes of this spec, a [scheme](@) is any sequence
+of 2--32 characters beginning with an ASCII letter and followed
+by any combination of ASCII letters, digits, or the symbols plus
+("+"), period ("."), or hyphen ("-").
+
+Here are some valid autolinks:
+
+```````````````````````````````` example
+
+.
+
http://foo.bar.baz

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

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

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

+````````````````````````````````
+
+
+Note that many strings that count as [absolute URIs] for
+purposes of this spec are not valid URIs, because their
+schemes are not registered or because of other problems
+with their syntax:
+
+```````````````````````````````` example
+
+.
+
a+b+c:d

+````````````````````````````````
+
+
+```````````````````````````````` example
+
+.
+
made-up-scheme://foo,bar

+````````````````````````````````
+
+
+```````````````````````````````` example
+
+.
+
http://../

+````````````````````````````````
+
+
+```````````````````````````````` example
+
+.
+
localhost:5001/foo

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

+````````````````````````````````
+
+
+Backslash-escapes do not work inside autolinks:
+
+```````````````````````````````` example
+
+.
+
http://example.com/\[\

+````````````````````````````````
+
+
+An [email autolink](@)
+consists of `<`, followed by an [email address],
+followed by `>`.  The link's label is the email address,
+and the URL is `mailto:` followed by the email address.
+
+An [email address](@),
+for these purposes, is anything that matches
+the [non-normative regex from the HTML5
+spec](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:
+
+```````````````````````````````` example
+
+.
+
foo@bar.example.com

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

+````````````````````````````````
+
+
+Backslash-escapes do not work inside email autolinks:
+
+```````````````````````````````` example
+
+.
+
<foo+@bar.example.com>

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+
+.
+
<m:abc>

+````````````````````````````````
+
+
+```````````````````````````````` example
+
+.
+
<foo.bar.baz>

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+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](@) consists of an ASCII letter
+followed by zero or more ASCII letters, digits, or
+hyphens (`-`).
+
+An [attribute](@) consists of spaces, tabs, and up to one line ending,
+an [attribute name], and an optional
+[attribute value specification].
+
+An [attribute name](@)
+consists of an ASCII letter, `_`, or `:`, followed by zero or more ASCII
+letters, digits, `_`, `.`, `:`, or `-`.  (Note:  This is the XML
+specification restricted to ASCII.  HTML5 is laxer.)
+
+An [attribute value specification](@)
+consists of optional spaces, tabs, and up to one line ending,
+a `=` character, optional spaces, tabs, and up to one line ending,
+and an [attribute value].
+
+An [attribute value](@)
+consists of an [unquoted attribute value],
+a [single-quoted attribute value], or a [double-quoted attribute value].
+
+An [unquoted attribute value](@)
+is a nonempty string of characters not
+including spaces, tabs, line endings, `"`, `'`, `=`, `<`, `>`, or `` ` ``.
+
+A [single-quoted attribute value](@)
+consists of `'`, zero or more
+characters not including `'`, and a final `'`.
+
+A [double-quoted attribute value](@)
+consists of `"`, zero or more
+characters not including `"`, and a final `"`.
+
+An [open tag](@) consists of a `<` character, a [tag name],
+zero or more [attributes], optional spaces, tabs, and up to one line ending,
+an optional `/` character, and a `>` character.
+
+A [closing tag](@) consists of the string ``.
+
+An [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](@)
+consists of the string ``, and the string
+`?>`.
+
+A [declaration](@) consists of the string ``, and the character `>`.
+
+A [CDATA section](@) consists of
+the string ``, and the string `]]>`.
+
+An [HTML tag](@) consists of an [open tag], a [closing tag],
+an [HTML comment], a [processing instruction], a [declaration],
+or a [CDATA section].
+
+Here are some simple open tags:
+
+```````````````````````````````` example
+
+.
+

+````````````````````````````````
+
+
+Empty elements:
+
+```````````````````````````````` example
+
+.
+

+````````````````````````````````
+
+
+Whitespace is allowed:
+
+```````````````````````````````` example
+
+.
+

+````````````````````````````````
+
+
+With attributes:
+
+```````````````````````````````` example
+
+.
+

+````````````````````````````````
+
+
+Custom tag names can be used:
+
+```````````````````````````````` example
+Foo 
+.
+
Foo 

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

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

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

+````````````````````````````````
+
+
+Comments:
+
+```````````````````````````````` example
+foo 
+.
+
foo 

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

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

+
foo <!-- foo--->

+````````````````````````````````
+
+
+Processing instructions:
+
+```````````````````````````````` example
+foo 
+.
+
foo 

+````````````````````````````````
+
+
+Declarations:
+
+```````````````````````````````` example
+foo 
+.
+
foo 

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

+````````````````````````````````
+
+
+Entity and numeric character references are preserved in HTML
+attributes:
+
+```````````````````````````````` example
+foo 
+.
+
foo 

+````````````````````````````````
+
+
+Backslash escapes do not work in HTML attributes:
+
+```````````````````````````````` example
+foo 
+.
+
foo 

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

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

+baz

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

+baz

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

+baz

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

+bar

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

+bar

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

+bar

+````````````````````````````````
+
+
+```````````````````````````````` example
+*foo\
+bar*
+.
+
foo

+bar

+````````````````````````````````
+
+
+Hard line breaks do not occur inside code spans
+
+```````````````````````````````` example
+`code  
+span`
+.
+
code   span

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

+````````````````````````````````
+
+
+or HTML tags:
+
+```````````````````````````````` example
+
+.
+

+````````````````````````````````
+
+
+```````````````````````````````` example
+
+.
+

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+### foo\
+.
+
foo\

+````````````````````````````````
+
+
+```````````````````````````````` example
+### foo  
+.
+
foo

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

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

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

+````````````````````````````````
+
+
+```````````````````````````````` example
+Foo χρῆν
+.
+
Foo χρῆν

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

+````````````````````````````````
+
+
+
+
+# Appendix: A parsing strategy
+
+In this appendix we describe some features of the parsing strategy
+used in the CommonMark reference implementations.
+
+## Overview
+
+Parsing has two phases:
+
+1. In the first phase, lines of input are consumed and the block
+structure of the document---its division into paragraphs, block quotes,
+list items, and so on---is constructed.  Text is assigned to these
+blocks but not parsed. Link reference definitions are parsed and a
+map of links is constructed.
+
+2. In the second phase, the raw text contents of paragraphs and headings
+are parsed into sequences of Markdown inline elements (strings,
+code spans, links, emphasis, and so on), using the map of link
+references constructed in phase 1.
+
+At each point in processing, the document is represented as a tree of
+**blocks**.  The root of the tree is a `document` block.  The `document`
+may have any number of other blocks as **children**.  These children
+may, in turn, have other blocks as children.  The last child of a block
+is normally considered **open**, meaning that subsequent lines of input
+can alter its contents.  (Blocks that are not open are **closed**.)
+Here, for example, is a possible document tree, with the open blocks
+marked by arrows:
+
+``` tree
+-> document
+  -> block_quote
+       paragraph
+         "Lorem ipsum dolor\nsit amet."
+    -> list (type=bullet tight=true bullet_char=-)
+         list_item
+           paragraph
+             "Qui *quodsi iracundia*"
+      -> list_item
+        -> paragraph
+             "aliquando id"
+```
+
+## Phase 1: block structure
+
+Each line that is processed has an effect on this tree.  The line is
+analyzed and, depending on its contents, the document may be altered
+in one or more of the following ways:
+
+1. One or more open blocks may be closed.
+2. One or more new blocks may be created as children of the
+   last open block.
+3. Text may be added to the last (deepest) open block remaining
+   on the tree.
+
+Once a line has been incorporated into the tree in this way,
+it can be discarded, so input can be read in a stream.
+
+For each line, we follow this procedure:
+
+1. First we iterate through the open blocks, starting with the
+root document, and descending through last children down to the last
+open block.  Each block imposes a condition that the line must satisfy
+if the block is to remain open.  For example, a block quote requires a
+`>` character.  A paragraph requires a non-blank line.
+In this phase we may match all or just some of the open
+blocks.  But we cannot close unmatched blocks yet, because we may have a
+[lazy continuation line].
+
+2.  Next, after consuming the continuation markers for existing
+blocks, we look for new block starts (e.g. `>` for a block quote).
+If we encounter a new block start, we close any blocks unmatched
+in step 1 before creating the new block as a child of the last
+matched container block.
+
+3.  Finally, we look at the remainder of the line (after block
+markers like `>`, list markers, and indentation have been consumed).
+This is text that can be incorporated into the last open
+block (a paragraph, code block, heading, or raw HTML).
+
+Setext headings are formed when we see a line of a paragraph
+that is a [setext heading underline].
+
+Reference link definitions are detected when a paragraph is closed;
+the accumulated text lines are parsed to see if they begin with
+one or more reference link definitions.  Any remainder becomes a
+normal paragraph.
+
+We can see how this works by considering how the tree above is
+generated by four lines of Markdown:
+
+``` 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"
+```
+
+## Phase 2: inline structure
+
+Once all of the input has been parsed, all open blocks are closed.
+
+We then "walk the tree," visiting every node, and parse raw
+string contents of paragraphs and headings as inlines.  At this
+point we have seen all the link reference definitions, so we can
+resolve reference links as we go.
+
+``` 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`.
+
+### An algorithm for parsing nested emphasis and links
+
+By far the trickiest part of inline parsing is handling emphasis,
+strong emphasis, links, and images.  This is done using the following
+algorithm.
+
+When we're parsing inlines and we hit either
+
+- a run of `*` or `_` characters, or
+- a `[` or `![`
+
+we insert a text node with these symbols as its literal content, and we
+add a pointer to this text node to the [delimiter stack](@).
+
+The [delimiter stack] is a doubly linked list.  Each
+element contains a pointer to a text node, plus information about
+
+- the type of delimiter (`[`, `![`, `*`, `_`)
+- the number of delimiters,
+- whether the delimiter is "active" (all are active to start), and
+- whether the delimiter is a potential opener, a potential closer,
+  or both (which depends on what sort of characters precede
+  and follow the delimiters).
+
+When we hit a `]` character, we call the *look for link or image*
+procedure (see below).
+
+When we hit the end of the input, we call the *process emphasis*
+procedure (see below), with `stack_bottom` = NULL.
+
+#### *look for link or image*
+
+Starting at the top of the delimiter stack, we look backwards
+through the stack for an opening `[` or `![` delimiter.
+
+- If we don't find one, we return a literal text node `]`.
+
+- If we do find one, but it's not *active*, we remove the inactive
+  delimiter from the stack, and return a literal text node `]`.
+
+- If we find one and it's active, then we parse ahead to see if
+  we have an inline link/image, reference link/image, compact reference
+  link/image, or shortcut reference link/image.
+
+  + If we don't, then we remove the opening delimiter from the
+    delimiter stack and return a literal text node `]`.
+
+  + If we do, then
+
+    * We return a link or image node whose children are the inlines
+      after the text node pointed to by the opening delimiter.
+
+    * We run *process emphasis* on these inlines, with the `[` opener
+      as `stack_bottom`.
+
+    * We remove the opening delimiter.
+
+    * If we have a link (and not an image), we also set all
+      `[` delimiters before the opening delimiter to *inactive*.  (This
+      will prevent us from getting links within links.)
+
+#### *process emphasis*
+
+Parameter `stack_bottom` sets a lower bound to how far we
+descend in the [delimiter stack].  If it is NULL, we can
+go all the way to the bottom.  Otherwise, we stop before
+visiting `stack_bottom`.
+
+Let `current_position` point to the element on the [delimiter stack]
+just above `stack_bottom` (or the first element if `stack_bottom`
+is NULL).
+
+We keep track of the `openers_bottom` for each delimiter
+type (`*`, `_`), indexed to the length of the closing delimiter run
+(modulo 3) and to whether the closing delimiter can also be an
+opener.  Initialize this to `stack_bottom`.
+
+Then we repeat the following until we run out of potential
+closers:
+
+- Move `current_position` forward in the delimiter stack (if needed)
+  until we find the first potential closer with delimiter `*` or `_`.
+  (This will be the potential closer closest
+  to the beginning of the input -- the first one in parse order.)
+
+- Now, look back in the stack (staying above `stack_bottom` and
+  the `openers_bottom` for this delimiter type) for the
+  first matching potential opener ("matching" means same delimiter).
+
+- If one is found:
+
+  + Figure out whether we have emphasis or strong emphasis:
+    if both closer and opener spans have length >= 2, we have
+    strong, otherwise regular.
+
+  + Insert an emph or strong emph node accordingly, after
+    the text node corresponding to the opener.
+
+  + Remove any delimiters between the opener and closer from
+    the delimiter stack.
+
+  + Remove 1 (for regular emph) or 2 (for strong emph) delimiters
+    from the opening and closing text nodes.  If they become empty
+    as a result, remove them and remove the corresponding element
+    of the delimiter stack.  If the closing node is removed, reset
+    `current_position` to the next element in the stack.
+
+- If none is found:
+
+  + Set `openers_bottom` to the element before `current_position`.
+    (We know that there are no openers for this kind of closer up to and
+    including this point, so this puts a lower bound on future searches.)
+
+  + If the closer at `current_position` is not a potential opener,
+    remove it from the delimiter stack (since we know it can't
+    be a closer either).
+
+  + Advance `current_position` to the next element in the stack.
+
+After we're done, we remove all delimiters above `stack_bottom` from the
+delimiter stack.
-- 
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