md4c

spec.txt (195431B)

---

 ---
 title: CommonMark Spec
 author: John MacFarlane
 version: 0.28
 date: '2017-08-01'
 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.
 > (<http://daringfireball.net/projects/markdown/>)
 
 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 `<p>` 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.
 
 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 newline (`U+000A`) or carriage return (`U+000D`),
 followed by a [line ending] or by the end of file.
 
 A [line ending](@) is a newline (`U+000A`), a carriage return
 (`U+000D`) not followed by a newline, or a carriage return and a
 following newline.
 
 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 [whitespace character](@) is a space
 (`U+0020`), tab (`U+0009`), newline (`U+000A`), line tabulation (`U+000B`),
 form feed (`U+000C`), or carriage return (`U+000D`).
 
 [Whitespace](@) is a sequence of one or more [whitespace
 characters].
 
 A [Unicode whitespace character](@) is
 any code point in the Unicode `Zs` general category, or a tab (`U+0009`),
 carriage return (`U+000D`), newline (`U+000A`), or form feed
 (`U+000C`).
 
 [Unicode whitespace](@) is a sequence of one
 or more [Unicode whitespace characters].
 
 A [space](@) is `U+0020`.
 
 A [non-whitespace character](@) is any character
 that is not a [whitespace character].
 
 An [ASCII punctuation character](@)
 is `!`, `"`, `#`, `$`, `%`, `&`, `'`, `(`, `)`,
 `*`, `+`, `,`, `-`, `.`, `/`, `:`, `;`, `<`, `=`, `>`, `?`, `@`,
 `[`, `\`, `]`, `^`, `_`, `` ` ``, `{`, `|`, `}`, or `~`.
 
 A [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 whitespace helps 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
 .
 <pre><code>foo→baz→→bim
 </code></pre>
 ````````````````````````````````
 
 ```````````````````````````````` example
   →foo→baz→→bim
 .
 <pre><code>foo→baz→→bim
 </code></pre>
 ````````````````````````````````
 
 ```````````````````````````````` example
     a→a
     ὐ→a
 .
 <pre><code>a→a
 ὐ→a
 </code></pre>
 ````````````````````````````````
 
 In the following example, a continuation paragraph of a list
 item is indented with a tab; this has exactly the same effect
 as indentation with four spaces would:
 
 ```````````````````````````````` example
   - foo
 
 →bar
 .
 <ul>
 <li>
 <p>foo</p>
 <p>bar</p>
 </li>
 </ul>
 ````````````````````````````````
 
 ```````````````````````````````` example
 - foo
 
 →→bar
 .
 <ul>
 <li>
 <p>foo</p>
 <pre><code>  bar
 </code></pre>
 </li>
 </ul>
 ````````````````````````````````
 
 Normally the `>` that begins a block quote may be followed
 optionally by a space, which is not considered part of the
 content.  In the following case `>` is followed by a tab,
 which is treated as if it were expanded into three spaces.
 Since one of these spaces is considered part of the
 delimiter, `foo` is considered to be indented six spaces
 inside the block quote context, so we get an indented
 code block starting with two spaces.
 
 ```````````````````````````````` example
 >→→foo
 .
 <blockquote>
 <pre><code>  foo
 </code></pre>
 </blockquote>
 ````````````````````````````````
 
 ```````````````````````````````` example
 -→→foo
 .
 <ul>
 <li>
 <pre><code>  foo
 </code></pre>
 </li>
 </ul>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
     foo
 →bar
 .
 <pre><code>foo
 bar
 </code></pre>
 ````````````````````````````````
 
 ```````````````````````````````` example
  - foo
    - bar
 → - baz
 .
 <ul>
 <li>foo
 <ul>
 <li>bar
 <ul>
 <li>baz</li>
 </ul>
 </li>
 </ul>
 </li>
 </ul>
 ````````````````````````````````
 
 ```````````````````````````````` example
 #→Foo
 .
 <h1>Foo</h1>
 ````````````````````````````````
 
 ```````````````````````````````` example
 *→*→*→
 .
 <hr />
 ````````````````````````````````
 
 
 ## Insecure characters
 
 For security reasons, the Unicode character `U+0000` must be replaced
 with the REPLACEMENT CHARACTER (`U+FFFD`).
 
 # 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`
 .
 <ul>
 <li>`one</li>
 <li>two`</li>
 </ul>
 ````````````````````````````````
 
 
 This means that parsing can proceed in two steps:  first, the block
 structure of the document can be discerned; second, text lines inside
 paragraphs, headings, and other block constructs can be parsed for inline
 structure.  The second step requires information about link reference
 definitions that will be available only at the end of the first
 step.  Note that the first step requires processing lines in sequence,
 but the second can be parallelized, since the inline parsing of
 one block element does not affect the inline parsing of any other.
 
 ## Container blocks and leaf blocks
 
 We can divide blocks into two types:
 [container block](@)s,
 which can contain other blocks, and [leaf block](@)s,
 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 0-3 spaces of indentation, followed by a sequence
 of three or more matching `-`, `_`, or `*` characters, each followed
 optionally by any number of spaces, forms a
 [thematic break](@).
 
 ```````````````````````````````` example
 ***
 ---
 ___
 .
 <hr />
 <hr />
 <hr />
 ````````````````````````````````
 
 
 Wrong characters:
 
 ```````````````````````````````` example
 +++
 .
 <p>+++</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ===
 .
 <p>===</p>
 ````````````````````````````````
 
 
 Not enough characters:
 
 ```````````````````````````````` example
 --
 **
 __
 .
 <p>--
 **
 __</p>
 ````````````````````````````````
 
 
 One to three spaces indent are allowed:
 
 ```````````````````````````````` example
  ***
   ***
    ***
 .
 <hr />
 <hr />
 <hr />
 ````````````````````````````````
 
 
 Four spaces is too many:
 
 ```````````````````````````````` example
     ***
 .
 <pre><code>***
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 Foo
     ***
 .
 <p>Foo
 ***</p>
 ````````````````````````````````
 
 
 More than three characters may be used:
 
 ```````````````````````````````` example
 _____________________________________
 .
 <hr />
 ````````````````````````````````
 
 
 Spaces are allowed between the characters:
 
 ```````````````````````````````` example
  - - -
 .
 <hr />
 ````````````````````````````````
 
 
 ```````````````````````````````` example
  **  * ** * ** * **
 .
 <hr />
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 -     -      -      -
 .
 <hr />
 ````````````````````````````````
 
 
 Spaces are allowed at the end:
 
 ```````````````````````````````` example
 - - - -    
 .
 <hr />
 ````````````````````````````````
 
 
 However, no other characters may occur in the line:
 
 ```````````````````````````````` example
 _ _ _ _ a
 
 a------
 
 ---a---
 .
 <p>_ _ _ _ a</p>
 <p>a------</p>
 <p>---a---</p>
 ````````````````````````````````
 
 
 It is required that all of the [non-whitespace characters] be the same.
 So, this is not a thematic break:
 
 ```````````````````````````````` example
  *-*
 .
 <p><em>-</em></p>
 ````````````````````````````````
 
 
 Thematic breaks do not need blank lines before or after:
 
 ```````````````````````````````` example
 - foo
 ***
 - bar
 .
 <ul>
 <li>foo</li>
 </ul>
 <hr />
 <ul>
 <li>bar</li>
 </ul>
 ````````````````````````````````
 
 
 Thematic breaks can interrupt a paragraph:
 
 ```````````````````````````````` example
 Foo
 ***
 bar
 .
 <p>Foo</p>
 <hr />
 <p>bar</p>
 ````````````````````````````````
 
 
 If a line of dashes that meets the above conditions for being a
 thematic break could also be interpreted as the underline of a [setext
 heading], the interpretation as a
 [setext heading] takes precedence. Thus, for example,
 this is a setext heading, not a paragraph followed by a thematic break:
 
 ```````````````````````````````` example
 Foo
 ---
 bar
 .
 <h2>Foo</h2>
 <p>bar</p>
 ````````````````````````````````
 
 
 When both a thematic break and a list item are possible
 interpretations of a line, the thematic break takes precedence:
 
 ```````````````````````````````` example
 * Foo
 * * *
 * Bar
 .
 <ul>
 <li>Foo</li>
 </ul>
 <hr />
 <ul>
 <li>Bar</li>
 </ul>
 ````````````````````````````````
 
 
 If you want a thematic break in a list item, use a different bullet:
 
 ```````````````````````````````` example
 - Foo
 - * * *
 .
 <ul>
 <li>Foo</li>
 <li>
 <hr />
 </li>
 </ul>
 ````````````````````````````````
 
 
 ## 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 a
 [space] or by the end of line. The optional closing sequence of `#`s must be
 preceded by a [space] and may be followed by spaces only.  The opening
 `#` character may be indented 0-3 spaces.  The raw contents of the
 heading are stripped of leading and trailing spaces 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
 .
 <h1>foo</h1>
 <h2>foo</h2>
 <h3>foo</h3>
 <h4>foo</h4>
 <h5>foo</h5>
 <h6>foo</h6>
 ````````````````````````````````
 
 
 More than six `#` characters is not a heading:
 
 ```````````````````````````````` example
 ####### foo
 .
 <p>####### foo</p>
 ````````````````````````````````
 
 
 At least one space 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
 .
 <p>#5 bolt</p>
 <p>#hashtag</p>
 ````````````````````````````````
 
 
 This is not a heading, because the first `#` is escaped:
 
 ```````````````````````````````` example
 \## foo
 .
 <p>## foo</p>
 ````````````````````````````````
 
 
 Contents are parsed as inlines:
 
 ```````````````````````````````` example
 # foo *bar* \*baz\*
 .
 <h1>foo <em>bar</em> *baz*</h1>
 ````````````````````````````````
 
 
 Leading and trailing blanks are ignored in parsing inline content:
 
 ```````````````````````````````` example
 #                  foo                     
 .
 <h1>foo</h1>
 ````````````````````````````````
 
 
 One to three spaces indentation are allowed:
 
 ```````````````````````````````` example
  ### foo
   ## foo
    # foo
 .
 <h3>foo</h3>
 <h2>foo</h2>
 <h1>foo</h1>
 ````````````````````````````````
 
 
 Four spaces are too much:
 
 ```````````````````````````````` example
     # foo
 .
 <pre><code># foo
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo
     # bar
 .
 <p>foo
 # bar</p>
 ````````````````````````````````
 
 
 A closing sequence of `#` characters is optional:
 
 ```````````````````````````````` example
 ## foo ##
   ###   bar    ###
 .
 <h2>foo</h2>
 <h3>bar</h3>
 ````````````````````````````````
 
 
 It need not be the same length as the opening sequence:
 
 ```````````````````````````````` example
 # foo ##################################
 ##### foo ##
 .
 <h1>foo</h1>
 <h5>foo</h5>
 ````````````````````````````````
 
 
 Spaces are allowed after the closing sequence:
 
 ```````````````````````````````` example
 ### foo ###     
 .
 <h3>foo</h3>
 ````````````````````````````````
 
 
 A sequence of `#` characters with anything but [spaces] following it
 is not a closing sequence, but counts as part of the contents of the
 heading:
 
 ```````````````````````````````` example
 ### foo ### b
 .
 <h3>foo ### b</h3>
 ````````````````````````````````
 
 
 The closing sequence must be preceded by a space:
 
 ```````````````````````````````` example
 # foo#
 .
 <h1>foo#</h1>
 ````````````````````````````````
 
 
 Backslash-escaped `#` characters do not count as part
 of the closing sequence:
 
 ```````````````````````````````` example
 ### foo \###
 ## foo #\##
 # foo \#
 .
 <h3>foo ###</h3>
 <h2>foo ###</h2>
 <h1>foo #</h1>
 ````````````````````````````````
 
 
 ATX headings need not be separated from surrounding content by blank
 lines, and they can interrupt paragraphs:
 
 ```````````````````````````````` example
 ****
 ## foo
 ****
 .
 <hr />
 <h2>foo</h2>
 <hr />
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 Foo bar
 # baz
 Bar foo
 .
 <p>Foo bar</p>
 <h1>baz</h1>
 <p>Bar foo</p>
 ````````````````````````````````
 
 
 ATX headings can be empty:
 
 ```````````````````````````````` example
 ## 
 #
 ### ###
 .
 <h2></h2>
 <h1></h1>
 <h3></h3>
 ````````````````````````````````
 
 
 ## Setext headings
 
 A [setext heading](@) consists of one or more
 lines of text, each containing at least one [non-whitespace
 character], with no more than 3 spaces 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 indentation and any number of trailing spaces.  If a line
 containing a single `-` can be interpreted as an
 empty [list items], it should be interpreted this way
 and not as a [setext 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*
 ---------
 .
 <h1>Foo <em>bar</em></h1>
 <h2>Foo <em>bar</em></h2>
 ````````````````````````````````
 
 
 The content of the header may span more than one line:
 
 ```````````````````````````````` example
 Foo *bar
 baz*
 ====
 .
 <h1>Foo <em>bar
 baz</em></h1>
 ````````````````````````````````
 
 
 The underlining can be any length:
 
 ```````````````````````````````` example
 Foo
 -------------------------
 
 Foo
 =
 .
 <h2>Foo</h2>
 <h1>Foo</h1>
 ````````````````````````````````
 
 
 The heading content can be indented up to three spaces, and need
 not line up with the underlining:
 
 ```````````````````````````````` example
    Foo
 ---
 
   Foo
 -----
 
   Foo
   ===
 .
 <h2>Foo</h2>
 <h2>Foo</h2>
 <h1>Foo</h1>
 ````````````````````````````````
 
 
 Four spaces indent is too much:
 
 ```````````````````````````````` example
     Foo
     ---
 
     Foo
 ---
 .
 <pre><code>Foo
 ---
 
 Foo
 </code></pre>
 <hr />
 ````````````````````````````````
 
 
 The setext heading underline can be indented up to three spaces, and
 may have trailing spaces:
 
 ```````````````````````````````` example
 Foo
    ----      
 .
 <h2>Foo</h2>
 ````````````````````````````````
 
 
 Four spaces is too much:
 
 ```````````````````````````````` example
 Foo
     ---
 .
 <p>Foo
 ---</p>
 ````````````````````````````````
 
 
 The setext heading underline cannot contain internal spaces:
 
 ```````````````````````````````` example
 Foo
 = =
 
 Foo
 --- -
 .
 <p>Foo
 = =</p>
 <p>Foo</p>
 <hr />
 ````````````````````````````````
 
 
 Trailing spaces in the content line do not cause a line break:
 
 ```````````````````````````````` example
 Foo  
 -----
 .
 <h2>Foo</h2>
 ````````````````````````````````
 
 
 Nor does a backslash at the end:
 
 ```````````````````````````````` example
 Foo\
 ----
 .
 <h2>Foo\</h2>
 ````````````````````````````````
 
 
 Since indicators of block structure take precedence over
 indicators of inline structure, the following are setext headings:
 
 ```````````````````````````````` example
 `Foo
 ----
 `
 
 <a title="a lot
 ---
 of dashes"/>
 .
 <h2>`Foo</h2>
 <p>`</p>
 <h2>&lt;a title=&quot;a lot</h2>
 <p>of dashes&quot;/&gt;</p>
 ````````````````````````````````
 
 
 The setext heading underline cannot be a [lazy continuation
 line] in a list item or block quote:
 
 ```````````````````````````````` example
 > Foo
 ---
 .
 <blockquote>
 <p>Foo</p>
 </blockquote>
 <hr />
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 > foo
 bar
 ===
 .
 <blockquote>
 <p>foo
 bar
 ===</p>
 </blockquote>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 - Foo
 ---
 .
 <ul>
 <li>Foo</li>
 </ul>
 <hr />
 ````````````````````````````````
 
 
 A blank line is needed between a paragraph and a following
 setext heading, since otherwise the paragraph becomes part
 of the heading's content:
 
 ```````````````````````````````` example
 Foo
 Bar
 ---
 .
 <h2>Foo
 Bar</h2>
 ````````````````````````````````
 
 
 But in general a blank line is not required before or after
 setext headings:
 
 ```````````````````````````````` example
 ---
 Foo
 ---
 Bar
 ---
 Baz
 .
 <hr />
 <h2>Foo</h2>
 <h2>Bar</h2>
 <p>Baz</p>
 ````````````````````````````````
 
 
 Setext headings cannot be empty:
 
 ```````````````````````````````` example
 
 ====
 .
 <p>====</p>
 ````````````````````````````````
 
 
 Setext heading text lines must not be interpretable as block
 constructs other than paragraphs.  So, the line of dashes
 in these examples gets interpreted as a thematic break:
 
 ```````````````````````````````` example
 ---
 ---
 .
 <hr />
 <hr />
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 - foo
 -----
 .
 <ul>
 <li>foo</li>
 </ul>
 <hr />
 ````````````````````````````````
 
 
 ```````````````````````````````` example
     foo
 ---
 .
 <pre><code>foo
 </code></pre>
 <hr />
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 > foo
 -----
 .
 <blockquote>
 <p>foo</p>
 </blockquote>
 <hr />
 ````````````````````````````````
 
 
 If you want a heading with `> foo` as its literal text, you can
 use backslash escapes:
 
 ```````````````````````````````` example
 \> foo
 ------
 .
 <h2>&gt; foo</h2>
 ````````````````````````````````
 
 
 **Compatibility note:**  Most existing Markdown implementations
 do not allow the text of setext headings to span multiple lines.
 But there is no consensus about how to interpret
 
 ``` 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
 .
 <p>Foo</p>
 <h2>bar</h2>
 <p>baz</p>
 ````````````````````````````````
 
 
 Authors who want interpretation 2 can put blank lines around
 the thematic break,
 
 ```````````````````````````````` example
 Foo
 bar
 
 ---
 
 baz
 .
 <p>Foo
 bar</p>
 <hr />
 <p>baz</p>
 ````````````````````````````````
 
 
 or use a thematic break that cannot count as a [setext heading
 underline], such as
 
 ```````````````````````````````` example
 Foo
 bar
 * * *
 baz
 .
 <p>Foo
 bar</p>
 <hr />
 <p>baz</p>
 ````````````````````````````````
 
 
 Authors who want interpretation 3 can use backslash escapes:
 
 ```````````````````````````````` example
 Foo
 bar
 \---
 baz
 .
 <p>Foo
 bar
 ---
 baz</p>
 ````````````````````````````````
 
 
 ## Indented code blocks
 
 An [indented code block](@) is composed of one or more
 [indented chunks] separated by blank lines.
 An [indented chunk](@) is a sequence of non-blank lines,
 each indented four or more spaces. 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
 .
 <pre><code>a simple
   indented code block
 </code></pre>
 ````````````````````````````````
 
 
 If there is any ambiguity between an interpretation of indentation
 as a code block and as indicating that material belongs to a [list
 item][list items], the list item interpretation takes precedence:
 
 ```````````````````````````````` example
   - foo
 
     bar
 .
 <ul>
 <li>
 <p>foo</p>
 <p>bar</p>
 </li>
 </ul>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 1.  foo
 
     - bar
 .
 <ol>
 <li>
 <p>foo</p>
 <ul>
 <li>bar</li>
 </ul>
 </li>
 </ol>
 ````````````````````````````````
 
 
 
 The contents of a code block are literal text, and do not get parsed
 as Markdown:
 
 ```````````````````````````````` example
     <a/>
     *hi*
 
     - one
 .
 <pre><code>&lt;a/&gt;
 *hi*
 
 - one
 </code></pre>
 ````````````````````````````````
 
 
 Here we have three chunks separated by blank lines:
 
 ```````````````````````````````` example
     chunk1
 
     chunk2
   
  
  
     chunk3
 .
 <pre><code>chunk1
 
 chunk2
 
 
 
 chunk3
 </code></pre>
 ````````````````````````````````
 
 
 Any initial spaces beyond four will be included in the content, even
 in interior blank lines:
 
 ```````````````````````````````` example
     chunk1
       
       chunk2
 .
 <pre><code>chunk1
   
   chunk2
 </code></pre>
 ````````````````````````````````
 
 
 An indented code block cannot interrupt a paragraph.  (This
 allows hanging indents and the like.)
 
 ```````````````````````````````` example
 Foo
     bar
 
 .
 <p>Foo
 bar</p>
 ````````````````````````````````
 
 
 However, any non-blank line with fewer than four leading spaces ends
 the code block immediately.  So a paragraph may occur immediately
 after indented code:
 
 ```````````````````````````````` example
     foo
 bar
 .
 <pre><code>foo
 </code></pre>
 <p>bar</p>
 ````````````````````````````````
 
 
 And indented code can occur immediately before and after other kinds of
 blocks:
 
 ```````````````````````````````` example
 # Heading
     foo
 Heading
 ------
     foo
 ----
 .
 <h1>Heading</h1>
 <pre><code>foo
 </code></pre>
 <h2>Heading</h2>
 <pre><code>foo
 </code></pre>
 <hr />
 ````````````````````````````````
 
 
 The first line can be indented more than four spaces:
 
 ```````````````````````````````` example
         foo
     bar
 .
 <pre><code>    foo
 bar
 </code></pre>
 ````````````````````````````````
 
 
 Blank lines preceding or following an indented code block
 are not included in it:
 
 ```````````````````````````````` example
 
     
     foo
     
 
 .
 <pre><code>foo
 </code></pre>
 ````````````````````````````````
 
 
 Trailing spaces are included in the code block's content:
 
 ```````````````````````````````` example
     foo  
 .
 <pre><code>foo  
 </code></pre>
 ````````````````````````````````
 
 
 
 ## Fenced code blocks
 
 A [code fence](@) is a sequence
 of at least three consecutive backtick characters (`` ` ``) or
 tildes (`~`).  (Tildes and backticks cannot be mixed.)
 A [fenced code block](@)
 begins with a code fence, indented no more than three spaces.
 
 The line with the opening code fence may optionally contain some text
 following the code fence; this is trimmed of leading and trailing
 spaces and called the [info string](@).
 The [info string] may not contain any backtick
 characters.  (The reason for this restriction is that otherwise
 some inline code would be incorrectly interpreted as the
 beginning of a fenced code block.)
 
 The content of the code block consists of all subsequent lines, until
 a closing [code fence] of the same type as the code block
 began with (backticks or tildes), and with at least as many backticks
 or tildes as the opening code fence.  If the leading code fence is
 indented N spaces, then up to N spaces of indentation are removed from
 each line of the content (if present).  (If a content line is not
 indented, it is preserved unchanged.  If it is indented less than N
 spaces, all of the indentation is removed.)
 
 The closing code fence may be indented up to three spaces, and may be
 followed only by spaces, which are ignored.  If the end of the
 containing block (or document) is reached and no closing code fence
 has been found, the code block contains all of the lines after the
 opening code fence until the end of the containing block (or
 document).  (An alternative spec would require backtracking in the
 event that a closing code fence is not found.  But this makes parsing
 much less efficient, and there seems to be no real down side to the
 behavior described here.)
 
 A fenced code block may interrupt a paragraph, and does not require
 a blank line either before or after.
 
 The content of a code fence is treated as literal text, not parsed
 as inlines.  The first word of the [info string] is typically used to
 specify the language of the code sample, and rendered in the `class`
 attribute of the `code` tag.  However, this spec does not mandate any
 particular treatment of the [info string].
 
 Here is a simple example with backticks:
 
 ```````````````````````````````` example
 ```
 <
  >
 ```
 .
 <pre><code>&lt;
  &gt;
 </code></pre>
 ````````````````````````````````
 
 
 With tildes:
 
 ```````````````````````````````` example
 ~~~
 <
  >
 ~~~
 .
 <pre><code>&lt;
  &gt;
 </code></pre>
 ````````````````````````````````
 
 
 The closing code fence must use the same character as the opening
 fence:
 
 ```````````````````````````````` example
 ```
 aaa
 ~~~
 ```
 .
 <pre><code>aaa
 ~~~
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ~~~
 aaa
 ```
 ~~~
 .
 <pre><code>aaa
 ```
 </code></pre>
 ````````````````````````````````
 
 
 The closing code fence must be at least as long as the opening fence:
 
 ```````````````````````````````` example
 ````
 aaa
 ```
 ``````
 .
 <pre><code>aaa
 ```
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ~~~~
 aaa
 ~~~
 ~~~~
 .
 <pre><code>aaa
 ~~~
 </code></pre>
 ````````````````````````````````
 
 
 Unclosed code blocks are closed by the end of the document
 (or the enclosing [block quote][block quotes] or [list item][list items]):
 
 ```````````````````````````````` example
 ```
 .
 <pre><code></code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 `````
 
 ```
 aaa
 .
 <pre><code>
 ```
 aaa
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 > ```
 > aaa
 
 bbb
 .
 <blockquote>
 <pre><code>aaa
 </code></pre>
 </blockquote>
 <p>bbb</p>
 ````````````````````````````````
 
 
 A code block can have all empty lines as its content:
 
 ```````````````````````````````` example
 ```
 
   
 ```
 .
 <pre><code>
   
 </code></pre>
 ````````````````````````````````
 
 
 A code block can be empty:
 
 ```````````````````````````````` example
 ```
 ```
 .
 <pre><code></code></pre>
 ````````````````````````````````
 
 
 Fences can be indented.  If the opening fence is indented,
 content lines will have equivalent opening indentation removed,
 if present:
 
 ```````````````````````````````` example
  ```
  aaa
 aaa
 ```
 .
 <pre><code>aaa
 aaa
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
   ```
 aaa
   aaa
 aaa
   ```
 .
 <pre><code>aaa
 aaa
 aaa
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
    ```
    aaa
     aaa
   aaa
    ```
 .
 <pre><code>aaa
  aaa
 aaa
 </code></pre>
 ````````````````````````````````
 
 
 Four spaces indentation produces an indented code block:
 
 ```````````````````````````````` example
     ```
     aaa
     ```
 .
 <pre><code>```
 aaa
 ```
 </code></pre>
 ````````````````````````````````
 
 
 Closing fences may be indented by 0-3 spaces, and their indentation
 need not match that of the opening fence:
 
 ```````````````````````````````` example
 ```
 aaa
   ```
 .
 <pre><code>aaa
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
    ```
 aaa
   ```
 .
 <pre><code>aaa
 </code></pre>
 ````````````````````````````````
 
 
 This is not a closing fence, because it is indented 4 spaces:
 
 ```````````````````````````````` example
 ```
 aaa
     ```
 .
 <pre><code>aaa
     ```
 </code></pre>
 ````````````````````````````````
 
 
 
 Code fences (opening and closing) cannot contain internal spaces:
 
 ```````````````````````````````` example
 ``` ```
 aaa
 .
 <p><code></code>
 aaa</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ~~~~~~
 aaa
 ~~~ ~~
 .
 <pre><code>aaa
 ~~~ ~~
 </code></pre>
 ````````````````````````````````
 
 
 Fenced code blocks can interrupt paragraphs, and can be followed
 directly by paragraphs, without a blank line between:
 
 ```````````````````````````````` example
 foo
 ```
 bar
 ```
 baz
 .
 <p>foo</p>
 <pre><code>bar
 </code></pre>
 <p>baz</p>
 ````````````````````````````````
 
 
 Other blocks can also occur before and after fenced code blocks
 without an intervening blank line:
 
 ```````````````````````````````` example
 foo
 ---
 ~~~
 bar
 ~~~
 # baz
 .
 <h2>foo</h2>
 <pre><code>bar
 </code></pre>
 <h1>baz</h1>
 ````````````````````````````````
 
 
 An [info string] can be provided after the opening code fence.
 Opening and closing spaces will be stripped, and the first word, prefixed
 with `language-`, is used as the value for the `class` attribute of the
 `code` element within the enclosing `pre` element.
 
 ```````````````````````````````` example
 ```ruby
 def foo(x)
   return 3
 end
 ```
 .
 <pre><code class="language-ruby">def foo(x)
   return 3
 end
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ~~~~    ruby startline=3 $%@#$
 def foo(x)
   return 3
 end
 ~~~~~~~
 .
 <pre><code class="language-ruby">def foo(x)
   return 3
 end
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ````;
 ````
 .
 <pre><code class="language-;"></code></pre>
 ````````````````````````````````
 
 
 [Info strings] for backtick code blocks cannot contain backticks:
 
 ```````````````````````````````` example
 ``` aa ```
 foo
 .
 <p><code>aa</code>
 foo</p>
 ````````````````````````````````
 
 
 Closing code fences cannot have [info strings]:
 
 ```````````````````````````````` example
 ```
 ``` aaa
 ```
 .
 <pre><code>``` aaa
 </code></pre>
 ````````````````````````````````
 
 
 
 ## 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 spaces
 optional indentation).  It ends with the first subsequent line that
 meets a matching [end condition](@), or the last line of
 the document or other [container 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 `<script`,
 `<pre`, or `<style` (case-insensitive), followed by whitespace,
 the string `>`, or the end of the line.\
 **End condition:**  line contains an end tag
 `</script>`, `</pre>`, or `</style>` (case-insensitive; it
 need not match the start tag).
 
 2.  **Start condition:** line begins with the string `<!--`.\
 **End condition:**  line contains the string `-->`.
 
 3.  **Start condition:** line begins with the string `<?`.\
 **End condition:** line contains the string `?>`.
 
 4.  **Start condition:** line begins with the string `<!`
 followed by an uppercase ASCII letter.\
 **End condition:** line contains the character `>`.
 
 5.  **Start condition:**  line begins with the string
 `<![CDATA[`.\
 **End condition:** line contains the string `]]>`.
 
 6.  **Start condition:** line begins the string `<` or `</`
 followed by one of the strings (case-insensitive) `address`,
 `article`, `aside`, `base`, `basefont`, `blockquote`, `body`,
 `caption`, `center`, `col`, `colgroup`, `dd`, `details`, `dialog`,
 `dir`, `div`, `dl`, `dt`, `fieldset`, `figcaption`, `figure`,
 `footer`, `form`, `frame`, `frameset`,
 `h1`, `h2`, `h3`, `h4`, `h5`, `h6`, `head`, `header`, `hr`,
 `html`, `iframe`, `legend`, `li`, `link`, `main`, `menu`, `menuitem`,
 `meta`, `nav`, `noframes`, `ol`, `optgroup`, `option`, `p`, `param`,
 `section`, `source`, `summary`, `table`, `tbody`, `td`,
 `tfoot`, `th`, `thead`, `title`, `tr`, `track`, `ul`, followed
 by [whitespace], the end of the line, the string `>`, or
 the string `/>`.\
 **End condition:** line is followed by a [blank line].
 
 7.  **Start condition:**  line begins with a complete [open tag]
 or [closing tag] (with any [tag name] other than `script`,
 `style`, or `pre`) followed only by [whitespace]
 or the end of the line.\
 **End condition:** line is followed by a [blank line].
 
 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
 <table>
   <tr>
     <td>
            hi
     </td>
   </tr>
 </table>
 
 okay.
 .
 <table>
   <tr>
     <td>
            hi
     </td>
   </tr>
 </table>
 <p>okay.</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
  <div>
   *hello*
          <foo><a>
 .
  <div>
   *hello*
          <foo><a>
 ````````````````````````````````
 
 
 A block can also start with a closing tag:
 
 ```````````````````````````````` example
 </div>
 *foo*
 .
 </div>
 *foo*
 ````````````````````````````````
 
 
 Here we have two HTML blocks with a Markdown paragraph between them:
 
 ```````````````````````````````` example
 <DIV CLASS="foo">
 
 *Markdown*
 
 </DIV>
 .
 <DIV CLASS="foo">
 <p><em>Markdown</em></p>
 </DIV>
 ````````````````````````````````
 
 
 The tag on the first line can be partial, as long
 as it is split where there would be whitespace:
 
 ```````````````````````````````` example
 <div id="foo"
   class="bar">
 </div>
 .
 <div id="foo"
   class="bar">
 </div>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <div id="foo" class="bar
   baz">
 </div>
 .
 <div id="foo" class="bar
   baz">
 </div>
 ````````````````````````````````
 
 
 An open tag need not be closed:
 ```````````````````````````````` example
 <div>
 *foo*
 
 *bar*
 .
 <div>
 *foo*
 <p><em>bar</em></p>
 ````````````````````````````````
 
 
 
 A partial tag need not even be completed (garbage
 in, garbage out):
 
 ```````````````````````````````` example
 <div id="foo"
 *hi*
 .
 <div id="foo"
 *hi*
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <div class
 foo
 .
 <div class
 foo
 ````````````````````````````````
 
 
 The initial tag doesn't even need to be a valid
 tag, as long as it starts like one:
 
 ```````````````````````````````` example
 <div *???-&&&-<---
 *foo*
 .
 <div *???-&&&-<---
 *foo*
 ````````````````````````````````
 
 
 In type 6 blocks, the initial tag need not be on a line by
 itself:
 
 ```````````````````````````````` example
 <div><a href="bar">*foo*</a></div>
 .
 <div><a href="bar">*foo*</a></div>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <table><tr><td>
 foo
 </td></tr></table>
 .
 <table><tr><td>
 foo
 </td></tr></table>
 ````````````````````````````````
 
 
 Everything until the next blank line or end of document
 gets included in the HTML block.  So, in the following
 example, what looks like a Markdown code block
 is actually part of the HTML block, which continues until a blank
 line or the end of the document is reached:
 
 ```````````````````````````````` example
 <div></div>
 ``` c
 int x = 33;
 ```
 .
 <div></div>
 ``` c
 int x = 33;
 ```
 ````````````````````````````````
 
 
 To start an [HTML block] with a tag that is *not* in the
 list of block-level tags in (6), you must put the tag by
 itself on the first line (and it must be complete):
 
 ```````````````````````````````` example
 <a href="foo">
 *bar*
 </a>
 .
 <a href="foo">
 *bar*
 </a>
 ````````````````````````````````
 
 
 In type 7 blocks, the [tag name] can be anything:
 
 ```````````````````````````````` example
 <Warning>
 *bar*
 </Warning>
 .
 <Warning>
 *bar*
 </Warning>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <i class="foo">
 *bar*
 </i>
 .
 <i class="foo">
 *bar*
 </i>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 </ins>
 *bar*
 .
 </ins>
 *bar*
 ````````````````````````````````
 
 
 These rules are designed to allow us to work with tags that
 can function as either block-level or inline-level tags.
 The `<del>` tag is a nice example.  We can surround content with
 `<del>` tags in three different ways.  In this case, we get a raw
 HTML block, because the `<del>` tag is on a line by itself:
 
 ```````````````````````````````` example
 <del>
 *foo*
 </del>
 .
 <del>
 *foo*
 </del>
 ````````````````````````````````
 
 
 In this case, we get a raw HTML block that just includes
 the `<del>` tag (because it ends with the following blank
 line).  So the contents get interpreted as CommonMark:
 
 ```````````````````````````````` example
 <del>
 
 *foo*
 
 </del>
 .
 <del>
 <p><em>foo</em></p>
 </del>
 ````````````````````````````````
 
 
 Finally, in this case, the `<del>` tags are interpreted
 as [raw HTML] *inside* the CommonMark paragraph.  (Because
 the tag is not on a line by itself, we get inline HTML
 rather than an [HTML block].)
 
 ```````````````````````````````` example
 <del>*foo*</del>
 .
 <p><del><em>foo</em></del></p>
 ````````````````````````````````
 
 
 HTML tags designed to contain literal content
 (`script`, `style`, `pre`), 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
 <pre language="haskell"><code>
 import Text.HTML.TagSoup
 
 main :: IO ()
 main = print $ parseTags tags
 </code></pre>
 okay
 .
 <pre language="haskell"><code>
 import Text.HTML.TagSoup
 
 main :: IO ()
 main = print $ parseTags tags
 </code></pre>
 <p>okay</p>
 ````````````````````````````````
 
 
 A script tag (type 1):
 
 ```````````````````````````````` example
 <script type="text/javascript">
 // JavaScript example
 
 document.getElementById("demo").innerHTML = "Hello JavaScript!";
 </script>
 okay
 .
 <script type="text/javascript">
 // JavaScript example
 
 document.getElementById("demo").innerHTML = "Hello JavaScript!";
 </script>
 <p>okay</p>
 ````````````````````````````````
 
 
 A style tag (type 1):
 
 ```````````````````````````````` example
 <style
   type="text/css">
 h1 {color:red;}
 
 p {color:blue;}
 </style>
 okay
 .
 <style
   type="text/css">
 h1 {color:red;}
 
 p {color:blue;}
 </style>
 <p>okay</p>
 ````````````````````````````````
 
 
 If there is no matching end tag, the block will end at the
 end of the document (or the enclosing [block quote][block quotes]
 or [list item][list items]):
 
 ```````````````````````````````` example
 <style
   type="text/css">
 
 foo
 .
 <style
   type="text/css">
 
 foo
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 > <div>
 > foo
 
 bar
 .
 <blockquote>
 <div>
 foo
 </blockquote>
 <p>bar</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 - <div>
 - foo
 .
 <ul>
 <li>
 <div>
 </li>
 <li>foo</li>
 </ul>
 ````````````````````````````````
 
 
 The end tag can occur on the same line as the start tag:
 
 ```````````````````````````````` example
 <style>p{color:red;}</style>
 *foo*
 .
 <style>p{color:red;}</style>
 <p><em>foo</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <!-- foo -->*bar*
 *baz*
 .
 <!-- foo -->*bar*
 <p><em>baz</em></p>
 ````````````````````````````````
 
 
 Note that anything on the last line after the
 end tag will be included in the [HTML block]:
 
 ```````````````````````````````` example
 <script>
 foo
 </script>1. *bar*
 .
 <script>
 foo
 </script>1. *bar*
 ````````````````````````````````
 
 
 A comment (type 2):
 
 ```````````````````````````````` example
 <!-- Foo
 
 bar
    baz -->
 okay
 .
 <!-- Foo
 
 bar
    baz -->
 <p>okay</p>
 ````````````````````````````````
 
 
 
 A processing instruction (type 3):
 
 ```````````````````````````````` example
 <?php
 
   echo '>';
 
 ?>
 okay
 .
 <?php
 
   echo '>';
 
 ?>
 <p>okay</p>
 ````````````````````````````````
 
 
 A declaration (type 4):
 
 ```````````````````````````````` example
 <!DOCTYPE html>
 .
 <!DOCTYPE html>
 ````````````````````````````````
 
 
 CDATA (type 5):
 
 ```````````````````````````````` example
 <![CDATA[
 function matchwo(a,b)
 {
   if (a < b && a < 0) then {
     return 1;
 
   } else {
 
     return 0;
   }
 }
 ]]>
 okay
 .
 <![CDATA[
 function matchwo(a,b)
 {
   if (a < b && a < 0) then {
     return 1;
 
   } else {
 
     return 0;
   }
 }
 ]]>
 <p>okay</p>
 ````````````````````````````````
 
 
 The opening tag can be indented 1-3 spaces, but not 4:
 
 ```````````````````````````````` example
   <!-- foo -->
 
     <!-- foo -->
 .
   <!-- foo -->
 <pre><code>&lt;!-- foo --&gt;
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
   <div>
 
     <div>
 .
   <div>
 <pre><code>&lt;div&gt;
 </code></pre>
 ````````````````````````````````
 
 
 An HTML block of types 1--6 can interrupt a paragraph, and need not be
 preceded by a blank line.
 
 ```````````````````````````````` example
 Foo
 <div>
 bar
 </div>
 .
 <p>Foo</p>
 <div>
 bar
 </div>
 ````````````````````````````````
 
 
 However, a following blank line is needed, except at the end of
 a document, and except for blocks of types 1--5, above:
 
 ```````````````````````````````` example
 <div>
 bar
 </div>
 *foo*
 .
 <div>
 bar
 </div>
 *foo*
 ````````````````````````````````
 
 
 HTML blocks of type 7 cannot interrupt a paragraph:
 
 ```````````````````````````````` example
 Foo
 <a href="bar">
 baz
 .
 <p>Foo
 <a href="bar">
 baz</p>
 ````````````````````````````````
 
 
 This rule differs from John Gruber's original Markdown syntax
 specification, which says:
 
 > The only restrictions are that block-level HTML elements —
 > e.g. `<div>`, `<table>`, `<pre>`, `<p>`, etc. — must be separated from
 > surrounding content by blank lines, and the start and end tags of the
 > block should not be indented with tabs or spaces.
 
 In some ways Gruber's rule is more restrictive than the one given
 here:
 
 - It requires that an HTML block be preceded by a blank line.
 - It does not allow the start tag to be indented.
 - It requires a matching end tag, which it also does not allow to
   be indented.
 
 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
 <div>
 
 *Emphasized* text.
 
 </div>
 .
 <div>
 <p><em>Emphasized</em> text.</p>
 </div>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <div>
 *Emphasized* text.
 </div>
 .
 <div>
 *Emphasized* text.
 </div>
 ````````````````````````````````
 
 
 Some Markdown implementations have adopted a convention of
 interpreting content inside tags as text if the open tag has
 the attribute `markdown=1`.  The rule given above seems a simpler and
 more elegant way of achieving the same expressive power, which is also
 much simpler to parse.
 
 The main potential drawback is that one can no longer paste HTML
 blocks into Markdown documents with 100% reliability.  However,
 *in most cases* this will work fine, because the blank lines in
 HTML are usually followed by HTML block tags.  For example:
 
 ```````````````````````````````` example
 <table>
 
 <tr>
 
 <td>
 Hi
 </td>
 
 </tr>
 
 </table>
 .
 <table>
 <tr>
 <td>
 Hi
 </td>
 </tr>
 </table>
 ````````````````````````````````
 
 
 There are problems, however, if the inner tags are indented
 *and* separated by spaces, as then they will be interpreted as
 an indented code block:
 
 ```````````````````````````````` example
 <table>
 
   <tr>
 
     <td>
       Hi
     </td>
 
   </tr>
 
 </table>
 .
 <table>
   <tr>
 <pre><code>&lt;td&gt;
   Hi
 &lt;/td&gt;
 </code></pre>
   </tr>
 </table>
 ````````````````````````````````
 
 
 Fortunately, blank lines are usually not necessary and can be
 deleted.  The exception is inside `<pre>` tags, but as described
 above, raw HTML blocks starting with `<pre>` *can* contain blank
 lines.
 
 ## Link reference definitions
 
 A [link reference definition](@)
 consists of a [link label], indented up to three spaces, followed
 by a colon (`:`), optional [whitespace] (including up to one
 [line ending]), a [link destination],
 optional [whitespace] (including up to one
 [line ending]), and an optional [link
 title], which if it is present must be separated
 from the [link destination] by [whitespace].
 No further [non-whitespace characters] may occur on the line.
 
 A [link reference definition]
 does not correspond to a structural element of a document.  Instead, it
 defines a label which can be used in [reference links]
 and reference-style [images] elsewhere in the document.  [Link
 reference definitions] can come either before or after the links that use
 them.
 
 ```````````````````````````````` example
 [foo]: /url "title"
 
 [foo]
 .
 <p><a href="/url" title="title">foo</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
    [foo]: 
       /url  
            'the title'  
 
 [foo]
 .
 <p><a href="/url" title="the title">foo</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [Foo*bar\]]:my_(url) 'title (with parens)'
 
 [Foo*bar\]]
 .
 <p><a href="my_(url)" title="title (with parens)">Foo*bar]</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [Foo bar]:
 <my%20url>
 'title'
 
 [Foo bar]
 .
 <p><a href="my%20url" title="title">Foo bar</a></p>
 ````````````````````````````````
 
 
 The title may extend over multiple lines:
 
 ```````````````````````````````` example
 [foo]: /url '
 title
 line1
 line2
 '
 
 [foo]
 .
 <p><a href="/url" title="
 title
 line1
 line2
 ">foo</a></p>
 ````````````````````````````````
 
 
 However, it may not contain a [blank line]:
 
 ```````````````````````````````` example
 [foo]: /url 'title
 
 with blank line'
 
 [foo]
 .
 <p>[foo]: /url 'title</p>
 <p>with blank line'</p>
 <p>[foo]</p>
 ````````````````````````````````
 
 
 The title may be omitted:
 
 ```````````````````````````````` example
 [foo]:
 /url
 
 [foo]
 .
 <p><a href="/url">foo</a></p>
 ````````````````````````````````
 
 
 The link destination may not be omitted:
 
 ```````````````````````````````` example
 [foo]:
 
 [foo]
 .
 <p>[foo]:</p>
 <p>[foo]</p>
 ````````````````````````````````
 
 
 Both title and destination can contain backslash escapes
 and literal backslashes:
 
 ```````````````````````````````` example
 [foo]: /url\bar\*baz "foo\"bar\baz"
 
 [foo]
 .
 <p><a href="/url%5Cbar*baz" title="foo&quot;bar\baz">foo</a></p>
 ````````````````````````````````
 
 
 A link can come before its corresponding definition:
 
 ```````````````````````````````` example
 [foo]
 
 [foo]: url
 .
 <p><a href="url">foo</a></p>
 ````````````````````````````````
 
 
 If there are several matching definitions, the first one takes
 precedence:
 
 ```````````````````````````````` example
 [foo]
 
 [foo]: first
 [foo]: second
 .
 <p><a href="first">foo</a></p>
 ````````````````````````````````
 
 
 As noted in the section on [Links], matching of labels is
 case-insensitive (see [matches]).
 
 ```````````````````````````````` example
 [FOO]: /url
 
 [Foo]
 .
 <p><a href="/url">Foo</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [ΑΓΩ]: /φου
 
 [αγω]
 .
 <p><a href="/%CF%86%CE%BF%CF%85">αγω</a></p>
 ````````````````````````````````
 
 
 Here is a link reference definition with no corresponding link.
 It contributes nothing to the document.
 
 ```````````````````````````````` example
 [foo]: /url
 .
 ````````````````````````````````
 
 
 Here is another one:
 
 ```````````````````````````````` example
 [
 foo
 ]: /url
 bar
 .
 <p>bar</p>
 ````````````````````````````````
 
 
 This is not a link reference definition, because there are
 [non-whitespace characters] after the title:
 
 ```````````````````````````````` example
 [foo]: /url "title" ok
 .
 <p>[foo]: /url &quot;title&quot; ok</p>
 ````````````````````````````````
 
 
 This is a link reference definition, but it has no title:
 
 ```````````````````````````````` example
 [foo]: /url
 "title" ok
 .
 <p>&quot;title&quot; ok</p>
 ````````````````````````````````
 
 
 This is not a link reference definition, because it is indented
 four spaces:
 
 ```````````````````````````````` example
     [foo]: /url "title"
 
 [foo]
 .
 <pre><code>[foo]: /url &quot;title&quot;
 </code></pre>
 <p>[foo]</p>
 ````````````````````````````````
 
 
 This is not a link reference definition, because it occurs inside
 a code block:
 
 ```````````````````````````````` example
 ```
 [foo]: /url
 ```
 
 [foo]
 .
 <pre><code>[foo]: /url
 </code></pre>
 <p>[foo]</p>
 ````````````````````````````````
 
 
 A [link reference definition] cannot interrupt a paragraph.
 
 ```````````````````````````````` example
 Foo
 [bar]: /baz
 
 [bar]
 .
 <p>Foo
 [bar]: /baz</p>
 <p>[bar]</p>
 ````````````````````````````````
 
 
 However, it can directly follow other block elements, such as headings
 and thematic breaks, and it need not be followed by a blank line.
 
 ```````````````````````````````` example
 # [Foo]
 [foo]: /url
 > bar
 .
 <h1><a href="/url">Foo</a></h1>
 <blockquote>
 <p>bar</p>
 </blockquote>
 ````````````````````````````````
 
 
 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]
 .
 <p><a href="/foo-url" title="foo">foo</a>,
 <a href="/bar-url" title="bar">bar</a>,
 <a href="/baz-url">baz</a></p>
 ````````````````````````````````
 
 
 [Link reference definitions] can occur
 inside block containers, like lists and block quotations.  They
 affect the entire document, not just the container in which they
 are defined:
 
 ```````````````````````````````` example
 [foo]
 
 > [foo]: /url
 .
 <p><a href="/url">foo</a></p>
 <blockquote>
 </blockquote>
 ````````````````````````````````
 
 
 
 ## 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
 [whitespace].
 
 A simple example with two paragraphs:
 
 ```````````````````````````````` example
 aaa
 
 bbb
 .
 <p>aaa</p>
 <p>bbb</p>
 ````````````````````````````````
 
 
 Paragraphs can contain multiple lines, but no blank lines:
 
 ```````````````````````````````` example
 aaa
 bbb
 
 ccc
 ddd
 .
 <p>aaa
 bbb</p>
 <p>ccc
 ddd</p>
 ````````````````````````````````
 
 
 Multiple blank lines between paragraph have no effect:
 
 ```````````````````````````````` example
 aaa
 
 
 bbb
 .
 <p>aaa</p>
 <p>bbb</p>
 ````````````````````````````````
 
 
 Leading spaces are skipped:
 
 ```````````````````````````````` example
   aaa
  bbb
 .
 <p>aaa
 bbb</p>
 ````````````````````````````````
 
 
 Lines after the first may be indented any amount, since indented
 code blocks cannot interrupt paragraphs.
 
 ```````````````````````````````` example
 aaa
              bbb
                                        ccc
 .
 <p>aaa
 bbb
 ccc</p>
 ````````````````````````````````
 
 
 However, the first line may be indented at most three spaces,
 or an indented code block will be triggered:
 
 ```````````````````````````````` example
    aaa
 bbb
 .
 <p>aaa
 bbb</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
     aaa
 bbb
 .
 <pre><code>aaa
 </code></pre>
 <p>bbb</p>
 ````````````````````````````````
 
 
 Final spaces are stripped before inline parsing, so a paragraph
 that ends with two or more spaces will not end with a [hard line
 break]:
 
 ```````````````````````````````` example
 aaa     
 bbb     
 .
 <p>aaa<br />
 bbb</p>
 ````````````````````````````````
 
 
 ## 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
 
   
 .
 <p>aaa</p>
 <h1>aaa</h1>
 ````````````````````````````````
 
 
 
 # Container blocks
 
 A [container block] is a block that has other
 blocks as its contents.  There are two basic kinds of container blocks:
 [block quotes] and [list items].
 [Lists] are meta-containers for [list items].
 
 We define the syntax for container blocks recursively.  The general
 form of the definition is:
 
 > If X is a sequence of blocks, then the result of
 > transforming X in such-and-such a way is a container of type Y
 > with these blocks as its content.
 
 So, we explain what counts as a block quote or list item by explaining
 how these can be *generated* from their contents. This should suffice
 to define the syntax, although it does not give a recipe for *parsing*
 these constructions.  (A recipe is provided below in the section entitled
 [A parsing strategy](#appendix-a-parsing-strategy).)
 
 ## Block quotes
 
 A [block quote marker](@)
 consists of 0-3 spaces of initial indent, plus (a) the character `>` together
 with a following space, or (b) a single character `>` not followed by a space.
 
 The following rules define [block quotes]:
 
 1.  **Basic case.**  If a string of lines *Ls* constitute a sequence
     of blocks *Bs*, then the result of prepending a [block quote
     marker] to the beginning of each line in *Ls*
     is a [block quote](#block-quotes) containing *Bs*.
 
 2.  **Laziness.**  If a string of lines *Ls* constitute a [block
     quote](#block-quotes) with contents *Bs*, then the result of deleting
     the initial [block quote marker] from one or
     more lines in which the next [non-whitespace character] after the [block
     quote marker] is [paragraph continuation
     text] is a block quote with *Bs* as its content.
     [Paragraph continuation text](@) is text
     that will be parsed as part of the content of a paragraph, but does
     not occur at the beginning of the paragraph.
 
 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
 .
 <blockquote>
 <h1>Foo</h1>
 <p>bar
 baz</p>
 </blockquote>
 ````````````````````````````````
 
 
 The spaces after the `>` characters can be omitted:
 
 ```````````````````````````````` example
 ># Foo
 >bar
 > baz
 .
 <blockquote>
 <h1>Foo</h1>
 <p>bar
 baz</p>
 </blockquote>
 ````````````````````````````````
 
 
 The `>` characters can be indented 1-3 spaces:
 
 ```````````````````````````````` example
    > # Foo
    > bar
  > baz
 .
 <blockquote>
 <h1>Foo</h1>
 <p>bar
 baz</p>
 </blockquote>
 ````````````````````````````````
 
 
 Four spaces gives us a code block:
 
 ```````````````````````````````` example
     > # Foo
     > bar
     > baz
 .
 <pre><code>&gt; # Foo
 &gt; bar
 &gt; baz
 </code></pre>
 ````````````````````````````````
 
 
 The Laziness clause allows us to omit the `>` before
 [paragraph continuation text]:
 
 ```````````````````````````````` example
 > # Foo
 > bar
 baz
 .
 <blockquote>
 <h1>Foo</h1>
 <p>bar
 baz</p>
 </blockquote>
 ````````````````````````````````
 
 
 A block quote can contain some lazy and some non-lazy
 continuation lines:
 
 ```````````````````````````````` example
 > bar
 baz
 > foo
 .
 <blockquote>
 <p>bar
 baz
 foo</p>
 </blockquote>
 ````````````````````````````````
 
 
 Laziness only applies to lines that would have been continuations of
 paragraphs had they been prepended with [block quote markers].
 For example, the `> ` cannot be omitted in the second line of
 
 ``` markdown
 > foo
 > ---
 ```
 
 without changing the meaning:
 
 ```````````````````````````````` example
 > foo
 ---
 .
 <blockquote>
 <p>foo</p>
 </blockquote>
 <hr />
 ````````````````````````````````
 
 
 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
 .
 <blockquote>
 <ul>
 <li>foo</li>
 </ul>
 </blockquote>
 <ul>
 <li>bar</li>
 </ul>
 ````````````````````````````````
 
 
 For the same reason, we can't omit the `> ` in front of
 subsequent lines of an indented or fenced code block:
 
 ```````````````````````````````` example
 >     foo
     bar
 .
 <blockquote>
 <pre><code>foo
 </code></pre>
 </blockquote>
 <pre><code>bar
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 > ```
 foo
 ```
 .
 <blockquote>
 <pre><code></code></pre>
 </blockquote>
 <p>foo</p>
 <pre><code></code></pre>
 ````````````````````````````````
 
 
 Note that in the following case, we have a [lazy
 continuation line]:
 
 ```````````````````````````````` example
 > foo
     - bar
 .
 <blockquote>
 <p>foo
 - bar</p>
 </blockquote>
 ````````````````````````````````
 
 
 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
 >
 .
 <blockquote>
 </blockquote>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 >
 >  
 > 
 .
 <blockquote>
 </blockquote>
 ````````````````````````````````
 
 
 A block quote can have initial or final blank lines:
 
 ```````````````````````````````` example
 >
 > foo
 >  
 .
 <blockquote>
 <p>foo</p>
 </blockquote>
 ````````````````````````````````
 
 
 A blank line always separates block quotes:
 
 ```````````````````````````````` example
 > foo
 
 > bar
 .
 <blockquote>
 <p>foo</p>
 </blockquote>
 <blockquote>
 <p>bar</p>
 </blockquote>
 ````````````````````````````````
 
 
 (Most current Markdown implementations, including John Gruber's
 original `Markdown.pl`, will parse this example as a single block quote
 with two paragraphs.  But it seems better to allow the author to decide
 whether two block quotes or one are wanted.)
 
 Consecutiveness means that if we put these block quotes together,
 we get a single block quote:
 
 ```````````````````````````````` example
 > foo
 > bar
 .
 <blockquote>
 <p>foo
 bar</p>
 </blockquote>
 ````````````````````````````````
 
 
 To get a block quote with two paragraphs, use:
 
 ```````````````````````````````` example
 > foo
 >
 > bar
 .
 <blockquote>
 <p>foo</p>
 <p>bar</p>
 </blockquote>
 ````````````````````````````````
 
 
 Block quotes can interrupt paragraphs:
 
 ```````````````````````````````` example
 foo
 > bar
 .
 <p>foo</p>
 <blockquote>
 <p>bar</p>
 </blockquote>
 ````````````````````````````````
 
 
 In general, blank lines are not needed before or after block
 quotes:
 
 ```````````````````````````````` example
 > aaa
 ***
 > bbb
 .
 <blockquote>
 <p>aaa</p>
 </blockquote>
 <hr />
 <blockquote>
 <p>bbb</p>
 </blockquote>
 ````````````````````````````````
 
 
 However, because of laziness, a blank line is needed between
 a block quote and a following paragraph:
 
 ```````````````````````````````` example
 > bar
 baz
 .
 <blockquote>
 <p>bar
 baz</p>
 </blockquote>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 > bar
 
 baz
 .
 <blockquote>
 <p>bar</p>
 </blockquote>
 <p>baz</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 > bar
 >
 baz
 .
 <blockquote>
 <p>bar</p>
 </blockquote>
 <p>baz</p>
 ````````````````````````````````
 
 
 It is a consequence of the Laziness rule that any number
 of initial `>`s may be omitted on a continuation line of a
 nested block quote:
 
 ```````````````````````````````` example
 > > > foo
 bar
 .
 <blockquote>
 <blockquote>
 <blockquote>
 <p>foo
 bar</p>
 </blockquote>
 </blockquote>
 </blockquote>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 >>> foo
 > bar
 >>baz
 .
 <blockquote>
 <blockquote>
 <blockquote>
 <p>foo
 bar
 baz</p>
 </blockquote>
 </blockquote>
 </blockquote>
 ````````````````````````````````
 
 
 When including an indented code block in a block quote,
 remember that the [block quote marker] includes
 both the `>` and a following space.  So *five spaces* are needed after
 the `>`:
 
 ```````````````````````````````` example
 >     code
 
 >    not code
 .
 <blockquote>
 <pre><code>code
 </code></pre>
 </blockquote>
 <blockquote>
 <p>not code</p>
 </blockquote>
 ````````````````````````````````
 
 
 
 ## 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 [non-whitespace character] and not separated
     from each other by more than one blank line, and *M* is a list
     marker of width *W* followed by 1 ≤ *N* ≤ 4 spaces, then the result
     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: 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.
 
 For example, let *Ls* be the lines
 
 ```````````````````````````````` example
 A paragraph
 with two lines.
 
     indented code
 
 > A block quote.
 .
 <p>A paragraph
 with two lines.</p>
 <pre><code>indented code
 </code></pre>
 <blockquote>
 <p>A block quote.</p>
 </blockquote>
 ````````````````````````````````
 
 
 And let *M* be the marker `1.`, and *N* = 2.  Then rule #1 says
 that the following is an ordered list item with start number 1,
 and the same contents as *Ls*:
 
 ```````````````````````````````` example
 1.  A paragraph
     with two lines.
 
         indented code
 
     > A block quote.
 .
 <ol>
 <li>
 <p>A paragraph
 with two lines.</p>
 <pre><code>indented code
 </code></pre>
 <blockquote>
 <p>A block quote.</p>
 </blockquote>
 </li>
 </ol>
 ````````````````````````````````
 
 
 The most important thing to notice is that the position of
 the text after the list marker determines how much indentation
 is needed in subsequent blocks in the list item.  If the list
 marker takes up two spaces, and there are three spaces between
 the list marker and the next [non-whitespace character], then blocks
 must be indented five spaces in order to fall under the list
 item.
 
 Here are some examples showing how far content must be indented to be
 put under the list item:
 
 ```````````````````````````````` example
 - one
 
  two
 .
 <ul>
 <li>one</li>
 </ul>
 <p>two</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 - one
 
   two
 .
 <ul>
 <li>
 <p>one</p>
 <p>two</p>
 </li>
 </ul>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
  -    one
 
      two
 .
 <ul>
 <li>one</li>
 </ul>
 <pre><code> two
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
  -    one
 
       two
 .
 <ul>
 <li>
 <p>one</p>
 <p>two</p>
 </li>
 </ul>
 ````````````````````````````````
 
 
 It is tempting to think of this in terms of columns:  the continuation
 blocks must be indented at least to the column of the first
 [non-whitespace character] after the list marker. However, that is not quite right.
 The spaces after the list marker determine how much relative indentation
 is needed.  Which column this indentation reaches will depend on
 how the list item is embedded in other constructions, as shown by
 this example:
 
 ```````````````````````````````` example
    > > 1.  one
 >>
 >>     two
 .
 <blockquote>
 <blockquote>
 <ol>
 <li>
 <p>one</p>
 <p>two</p>
 </li>
 </ol>
 </blockquote>
 </blockquote>
 ````````````````````````````````
 
 
 Here `two` occurs in the same column as the list marker `1.`,
 but is actually contained in the list item, because there is
 sufficient indentation after the last containing blockquote marker.
 
 The converse is also possible.  In the following example, the word `two`
 occurs far to the right of the initial text of the list item, `one`, but
 it is not considered part of the list item, because it is not indented
 far enough past the blockquote marker:
 
 ```````````````````````````````` example
 >>- one
 >>
   >  > two
 .
 <blockquote>
 <blockquote>
 <ul>
 <li>one</li>
 </ul>
 <p>two</p>
 </blockquote>
 </blockquote>
 ````````````````````````````````
 
 
 Note that at least one space is needed between the list marker and
 any following content, so these are not list items:
 
 ```````````````````````````````` example
 -one
 
 2.two
 .
 <p>-one</p>
 <p>2.two</p>
 ````````````````````````````````
 
 
 A list item may contain blocks that are separated by more than
 one blank line.
 
 ```````````````````````````````` example
 - foo
 
 
   bar
 .
 <ul>
 <li>
 <p>foo</p>
 <p>bar</p>
 </li>
 </ul>
 ````````````````````````````````
 
 
 A list item may contain any kind of block:
 
 ```````````````````````````````` example
 1.  foo
 
     ```
     bar
     ```
 
     baz
 
     > bam
 .
 <ol>
 <li>
 <p>foo</p>
 <pre><code>bar
 </code></pre>
 <p>baz</p>
 <blockquote>
 <p>bam</p>
 </blockquote>
 </li>
 </ol>
 ````````````````````````````````
 
 
 A list item that contains an indented code block will preserve
 empty lines within the code block verbatim.
 
 ```````````````````````````````` example
 - Foo
 
       bar
 
 
       baz
 .
 <ul>
 <li>
 <p>Foo</p>
 <pre><code>bar
 
 
 baz
 </code></pre>
 </li>
 </ul>
 ````````````````````````````````
 
 Note that ordered list start numbers must be nine digits or less:
 
 ```````````````````````````````` example
 123456789. ok
 .
 <ol start="123456789">
 <li>ok</li>
 </ol>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 1234567890. not ok
 .
 <p>1234567890. not ok</p>
 ````````````````````````````````
 
 
 A start number may begin with 0s:
 
 ```````````````````````````````` example
 0. ok
 .
 <ol start="0">
 <li>ok</li>
 </ol>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 003. ok
 .
 <ol start="3">
 <li>ok</li>
 </ol>
 ````````````````````````````````
 
 
 A start number may not be negative:
 
 ```````````````````````````````` example
 -1. not ok
 .
 <p>-1. not ok</p>
 ````````````````````````````````
 
 
 
 2.  **Item starting with indented code.**  If a sequence of lines *Ls*
     constitute a sequence of blocks *Bs* starting with an indented code
     block and not separated from each other by more than one blank line,
     and *M* is a list marker of width *W* followed by
     one space, then the result of prepending *M* and the following
     space to the first line of *Ls*, and indenting subsequent lines of
     *Ls* by *W + 1* spaces, is a list item with *Bs* as its contents.
     If a line is empty, then it need not be indented.  The type of the
     list item (bullet or ordered) is determined by the type of its list
     marker.  If the list item is ordered, then it is also assigned a
     start number, based on the ordered list marker.
 
 An indented code block will have to be indented four spaces beyond
 the edge of the region where text will be included in the list item.
 In the following case that is 6 spaces:
 
 ```````````````````````````````` example
 - foo
 
       bar
 .
 <ul>
 <li>
 <p>foo</p>
 <pre><code>bar
 </code></pre>
 </li>
 </ul>
 ````````````````````````````````
 
 
 And in this case it is 11 spaces:
 
 ```````````````````````````````` example
   10.  foo
 
            bar
 .
 <ol start="10">
 <li>
 <p>foo</p>
 <pre><code>bar
 </code></pre>
 </li>
 </ol>
 ````````````````````````````````
 
 
 If the *first* block in the list item is an indented code block,
 then by rule #2, the contents must be indented *one* space after the
 list marker:
 
 ```````````````````````````````` example
     indented code
 
 paragraph
 
     more code
 .
 <pre><code>indented code
 </code></pre>
 <p>paragraph</p>
 <pre><code>more code
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 1.     indented code
 
    paragraph
 
        more code
 .
 <ol>
 <li>
 <pre><code>indented code
 </code></pre>
 <p>paragraph</p>
 <pre><code>more code
 </code></pre>
 </li>
 </ol>
 ````````````````````````````````
 
 
 Note that an additional space indent is interpreted as space
 inside the code block:
 
 ```````````````````````````````` example
 1.      indented code
 
    paragraph
 
        more code
 .
 <ol>
 <li>
 <pre><code> indented code
 </code></pre>
 <p>paragraph</p>
 <pre><code>more code
 </code></pre>
 </li>
 </ol>
 ````````````````````````````````
 
 
 Note that rules #1 and #2 only apply to two cases:  (a) cases
 in which the lines to be included in a list item begin with a
 [non-whitespace character], and (b) cases in which
 they begin with an indented code
 block.  In a case like the following, where the first block begins with
 a three-space indent, the rules do not allow us to form a list item by
 indenting the whole thing and prepending a list marker:
 
 ```````````````````````````````` example
    foo
 
 bar
 .
 <p>foo</p>
 <p>bar</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 -    foo
 
   bar
 .
 <ul>
 <li>foo</li>
 </ul>
 <p>bar</p>
 ````````````````````````````````
 
 
 This is not a significant restriction, because when a block begins
 with 1-3 spaces indent, the indentation can always be removed without
 a change in interpretation, allowing rule #1 to be applied.  So, in
 the above case:
 
 ```````````````````````````````` example
 -  foo
 
    bar
 .
 <ul>
 <li>
 <p>foo</p>
 <p>bar</p>
 </li>
 </ul>
 ````````````````````````````````
 
 
 3.  **Item starting with a blank line.**  If a sequence of lines *Ls*
     starting with a single [blank line] constitute a (possibly empty)
     sequence of blocks *Bs*, not separated from each other by more than
     one blank line, and *M* is a list marker of width *W*,
     then the result of prepending *M* 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.
 
 Here are some list items that start with a blank line but are not empty:
 
 ```````````````````````````````` example
 -
   foo
 -
   ```
   bar
   ```
 -
       baz
 .
 <ul>
 <li>foo</li>
 <li>
 <pre><code>bar
 </code></pre>
 </li>
 <li>
 <pre><code>baz
 </code></pre>
 </li>
 </ul>
 ````````````````````````````````
 
 When the list item starts with a blank line, the number of spaces
 following the list marker doesn't change the required indentation:
 
 ```````````````````````````````` example
 -   
   foo
 .
 <ul>
 <li>foo</li>
 </ul>
 ````````````````````````````````
 
 
 A list item can begin with at most one blank line.
 In the following example, `foo` is not part of the list
 item:
 
 ```````````````````````````````` example
 -
 
   foo
 .
 <ul>
 <li></li>
 </ul>
 <p>foo</p>
 ````````````````````````````````
 
 
 Here is an empty bullet list item:
 
 ```````````````````````````````` example
 - foo
 -
 - bar
 .
 <ul>
 <li>foo</li>
 <li></li>
 <li>bar</li>
 </ul>
 ````````````````````````````````
 
 
 It does not matter whether there are spaces following the [list marker]:
 
 ```````````````````````````````` example
 - foo
 -   
 - bar
 .
 <ul>
 <li>foo</li>
 <li></li>
 <li>bar</li>
 </ul>
 ````````````````````````````````
 
 
 Here is an empty ordered list item:
 
 ```````````````````````````````` example
 1. foo
 2.
 3. bar
 .
 <ol>
 <li>foo</li>
 <li></li>
 <li>bar</li>
 </ol>
 ````````````````````````````````
 
 
 A list may start or end with an empty list item:
 
 ```````````````````````````````` example
 *
 .
 <ul>
 <li></li>
 </ul>
 ````````````````````````````````
 
 However, an empty list item cannot interrupt a paragraph:
 
 ```````````````````````````````` example
 foo
 *
 
 foo
 1.
 .
 <p>foo
 *</p>
 <p>foo
 1.</p>
 ````````````````````````````````
 
 
 4.  **Indentation.**  If a sequence of lines *Ls* constitutes a list item
     according to rule #1, #2, or #3, then the result of indenting each line
     of *Ls* by 1-3 spaces (the same for each line) also constitutes a
     list item with the same contents and attributes.  If a line is
     empty, then it need not be indented.
 
 Indented one space:
 
 ```````````````````````````````` example
  1.  A paragraph
      with two lines.
 
          indented code
 
      > A block quote.
 .
 <ol>
 <li>
 <p>A paragraph
 with two lines.</p>
 <pre><code>indented code
 </code></pre>
 <blockquote>
 <p>A block quote.</p>
 </blockquote>
 </li>
 </ol>
 ````````````````````````````````
 
 
 Indented two spaces:
 
 ```````````````````````````````` example
   1.  A paragraph
       with two lines.
 
           indented code
 
       > A block quote.
 .
 <ol>
 <li>
 <p>A paragraph
 with two lines.</p>
 <pre><code>indented code
 </code></pre>
 <blockquote>
 <p>A block quote.</p>
 </blockquote>
 </li>
 </ol>
 ````````````````````````````````
 
 
 Indented three spaces:
 
 ```````````````````````````````` example
    1.  A paragraph
        with two lines.
 
            indented code
 
        > A block quote.
 .
 <ol>
 <li>
 <p>A paragraph
 with two lines.</p>
 <pre><code>indented code
 </code></pre>
 <blockquote>
 <p>A block quote.</p>
 </blockquote>
 </li>
 </ol>
 ````````````````````````````````
 
 
 Four spaces indent gives a code block:
 
 ```````````````````````````````` example
     1.  A paragraph
         with two lines.
 
             indented code
 
         > A block quote.
 .
 <pre><code>1.  A paragraph
     with two lines.
 
         indented code
 
     &gt; A block quote.
 </code></pre>
 ````````````````````````````````
 
 
 
 5.  **Laziness.**  If a string of lines *Ls* constitute a [list
     item](#list-items) with contents *Bs*, then the result of deleting
     some or all of the indentation from one or more lines in which the
     next [non-whitespace character] after the indentation is
     [paragraph continuation text] is a
     list item with the same contents and attributes.  The unindented
     lines are called
     [lazy continuation line](@)s.
 
 Here is an example with [lazy continuation lines]:
 
 ```````````````````````````````` example
   1.  A paragraph
 with two lines.
 
           indented code
 
       > A block quote.
 .
 <ol>
 <li>
 <p>A paragraph
 with two lines.</p>
 <pre><code>indented code
 </code></pre>
 <blockquote>
 <p>A block quote.</p>
 </blockquote>
 </li>
 </ol>
 ````````````````````````````````
 
 
 Indentation can be partially deleted:
 
 ```````````````````````````````` example
   1.  A paragraph
     with two lines.
 .
 <ol>
 <li>A paragraph
 with two lines.</li>
 </ol>
 ````````````````````````````````
 
 
 These examples show how laziness can work in nested structures:
 
 ```````````````````````````````` example
 > 1. > Blockquote
 continued here.
 .
 <blockquote>
 <ol>
 <li>
 <blockquote>
 <p>Blockquote
 continued here.</p>
 </blockquote>
 </li>
 </ol>
 </blockquote>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 > 1. > Blockquote
 > continued here.
 .
 <blockquote>
 <ol>
 <li>
 <blockquote>
 <p>Blockquote
 continued here.</p>
 </blockquote>
 </li>
 </ol>
 </blockquote>
 ````````````````````````````````
 
 
 
 6.  **That's all.** Nothing that is not counted as a list item by rules
     #1--5 counts as a [list item](#list-items).
 
 The rules for sublists follow from the general rules above.  A sublist
 must be indented the same number of spaces a paragraph would need to be
 in order to be included in the list item.
 
 So, in this case we need two spaces indent:
 
 ```````````````````````````````` example
 - foo
   - bar
     - baz
       - boo
 .
 <ul>
 <li>foo
 <ul>
 <li>bar
 <ul>
 <li>baz
 <ul>
 <li>boo</li>
 </ul>
 </li>
 </ul>
 </li>
 </ul>
 </li>
 </ul>
 ````````````````````````````````
 
 
 One is not enough:
 
 ```````````````````````````````` example
 - foo
  - bar
   - baz
    - boo
 .
 <ul>
 <li>foo</li>
 <li>bar</li>
 <li>baz</li>
 <li>boo</li>
 </ul>
 ````````````````````````````````
 
 
 Here we need four, because the list marker is wider:
 
 ```````````````````````````````` example
 10) foo
     - bar
 .
 <ol start="10">
 <li>foo
 <ul>
 <li>bar</li>
 </ul>
 </li>
 </ol>
 ````````````````````````````````
 
 
 Three is not enough:
 
 ```````````````````````````````` example
 10) foo
    - bar
 .
 <ol start="10">
 <li>foo</li>
 </ol>
 <ul>
 <li>bar</li>
 </ul>
 ````````````````````````````````
 
 
 A list may be the first block in a list item:
 
 ```````````````````````````````` example
 - - foo
 .
 <ul>
 <li>
 <ul>
 <li>foo</li>
 </ul>
 </li>
 </ul>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 1. - 2. foo
 .
 <ol>
 <li>
 <ul>
 <li>
 <ol start="2">
 <li>foo</li>
 </ol>
 </li>
 </ul>
 </li>
 </ol>
 ````````````````````````````````
 
 
 A list item can contain a heading:
 
 ```````````````````````````````` example
 - # Foo
 - Bar
   ---
   baz
 .
 <ul>
 <li>
 <h1>Foo</h1>
 </li>
 <li>
 <h2>Bar</h2>
 baz</li>
 </ul>
 ````````````````````````````````
 
 
 ### 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
 <ul>
 <li>foo</li>
 </ul>
 <p>bar</p>
 <ul>
 <li>baz</li>
 </ul>
 ```
 
 as the four-space rule demands, rather than a single list,
 
 ``` html
 <ul>
 <li>
 <p>foo</p>
 <p>bar</p>
 <ul>
 <li>baz</li>
 </ul>
 </li>
 </ul>
 ```
 
 The choice of four spaces is arbitrary.  It can be learned, but it is
 not likely to be guessed, and it trips up beginners regularly.
 
 Would it help to adopt a two-space rule?  The problem is that such
 a rule, together with the rule allowing 1--3 spaces indentation of the
 initial list marker, allows text that is indented *less than* the
 original list marker to be included in the list item. For example,
 `Markdown.pl` parses
 
 ``` markdown
    - one
 
   two
 ```
 
 as a single list item, with `two` a continuation paragraph:
 
 ``` html
 <ul>
 <li>
 <p>one</p>
 <p>two</p>
 </li>
 </ul>
 ```
 
 and similarly
 
 ``` markdown
 >   - one
 >
 >  two
 ```
 
 as
 
 ``` html
 <blockquote>
 <ul>
 <li>
 <p>one</p>
 <p>two</p>
 </li>
 </ul>
 </blockquote>
 ```
 
 This is extremely unintuitive.
 
 Rather than requiring a fixed indent from the margin, we could require
 a fixed indent (say, two spaces, or even one space) from the list marker (which
 may itself be indented).  This proposal would remove the last anomaly
 discussed.  Unlike the spec presented above, it would count the following
 as a list item with a subparagraph, even though the paragraph `bar`
 is not indented as far as the first paragraph `foo`:
 
 ``` 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 `<p>` tags, while paragraphs in a tight list are not.)
 
 Changing the bullet or ordered list delimiter starts a new list:
 
 ```````````````````````````````` example
 - foo
 - bar
 + baz
 .
 <ul>
 <li>foo</li>
 <li>bar</li>
 </ul>
 <ul>
 <li>baz</li>
 </ul>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 1. foo
 2. bar
 3) baz
 .
 <ol>
 <li>foo</li>
 <li>bar</li>
 </ol>
 <ol start="3">
 <li>baz</li>
 </ol>
 ````````````````````````````````
 
 
 In CommonMark, a list can interrupt a paragraph. That is,
 no blank line is needed to separate a paragraph from a following
 list:
 
 ```````````````````````````````` example
 Foo
 - bar
 - baz
 .
 <p>Foo</p>
 <ul>
 <li>bar</li>
 <li>baz</li>
 </ul>
 ````````````````````````````````
 
 `Markdown.pl` does not allow this, through fear of triggering a list
 via a numeral in a hard-wrapped line:
 
 ``` 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 `<p>` 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.
 .
 <p>The number of windows in my house is
 14.  The number of doors is 6.</p>
 ````````````````````````````````
 
 We may still get an unintended result in cases like
 
 ```````````````````````````````` example
 The number of windows in my house is
 1.  The number of doors is 6.
 .
 <p>The number of windows in my house is</p>
 <ol>
 <li>The number of doors is 6.</li>
 </ol>
 ````````````````````````````````
 
 but this rule should prevent most spurious list captures.
 
 There can be any number of blank lines between items:
 
 ```````````````````````````````` example
 - foo
 
 - bar
 
 
 - baz
 .
 <ul>
 <li>
 <p>foo</p>
 </li>
 <li>
 <p>bar</p>
 </li>
 <li>
 <p>baz</p>
 </li>
 </ul>
 ````````````````````````````````
 
 ```````````````````````````````` example
 - foo
   - bar
     - baz
 
 
       bim
 .
 <ul>
 <li>foo
 <ul>
 <li>bar
 <ul>
 <li>
 <p>baz</p>
 <p>bim</p>
 </li>
 </ul>
 </li>
 </ul>
 </li>
 </ul>
 ````````````````````````````````
 
 
 To separate consecutive lists of the same type, or to separate a
 list from an indented code block that would otherwise be parsed
 as a subparagraph of the final list item, you can insert a blank HTML
 comment:
 
 ```````````````````````````````` example
 - foo
 - bar
 
 <!-- -->
 
 - baz
 - bim
 .
 <ul>
 <li>foo</li>
 <li>bar</li>
 </ul>
 <!-- -->
 <ul>
 <li>baz</li>
 <li>bim</li>
 </ul>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 -   foo
 
     notcode
 
 -   foo
 
 <!-- -->
 
     code
 .
 <ul>
 <li>
 <p>foo</p>
 <p>notcode</p>
 </li>
 <li>
 <p>foo</p>
 </li>
 </ul>
 <!-- -->
 <pre><code>code
 </code></pre>
 ````````````````````````````````
 
 
 List items need not be indented to the same level.  The following
 list items will be treated as items at the same list level,
 since none is indented enough to belong to the previous list
 item:
 
 ```````````````````````````````` example
 - a
  - b
   - c
    - d
     - e
    - f
   - g
  - h
 - i
 .
 <ul>
 <li>a</li>
 <li>b</li>
 <li>c</li>
 <li>d</li>
 <li>e</li>
 <li>f</li>
 <li>g</li>
 <li>h</li>
 <li>i</li>
 </ul>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 1. a
 
   2. b
 
     3. c
 .
 <ol>
 <li>
 <p>a</p>
 </li>
 <li>
 <p>b</p>
 </li>
 <li>
 <p>c</p>
 </li>
 </ol>
 ````````````````````````````````
 
 
 This is a loose list, because there is a blank line between
 two of the list items:
 
 ```````````````````````````````` example
 - a
 - b
 
 - c
 .
 <ul>
 <li>
 <p>a</p>
 </li>
 <li>
 <p>b</p>
 </li>
 <li>
 <p>c</p>
 </li>
 </ul>
 ````````````````````````````````
 
 
 So is this, with a empty second item:
 
 ```````````````````````````````` example
 * a
 *
 
 * c
 .
 <ul>
 <li>
 <p>a</p>
 </li>
 <li></li>
 <li>
 <p>c</p>
 </li>
 </ul>
 ````````````````````````````````
 
 
 These are loose lists, even though there is no space between the items,
 because one of the items directly contains two block-level elements
 with a blank line between them:
 
 ```````````````````````````````` example
 - a
 - b
 
   c
 - d
 .
 <ul>
 <li>
 <p>a</p>
 </li>
 <li>
 <p>b</p>
 <p>c</p>
 </li>
 <li>
 <p>d</p>
 </li>
 </ul>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 - a
 - b
 
   [ref]: /url
 - d
 .
 <ul>
 <li>
 <p>a</p>
 </li>
 <li>
 <p>b</p>
 </li>
 <li>
 <p>d</p>
 </li>
 </ul>
 ````````````````````````````````
 
 
 This is a tight list, because the blank lines are in a code block:
 
 ```````````````````````````````` example
 - a
 - ```
   b
 
 
   ```
 - c
 .
 <ul>
 <li>a</li>
 <li>
 <pre><code>b
 
 
 </code></pre>
 </li>
 <li>c</li>
 </ul>
 ````````````````````````````````
 
 
 This is a tight list, because the blank line is between two
 paragraphs of a sublist.  So the sublist is loose while
 the outer list is tight:
 
 ```````````````````````````````` example
 - a
   - b
 
     c
 - d
 .
 <ul>
 <li>a
 <ul>
 <li>
 <p>b</p>
 <p>c</p>
 </li>
 </ul>
 </li>
 <li>d</li>
 </ul>
 ````````````````````````````````
 
 
 This is a tight list, because the blank line is inside the
 block quote:
 
 ```````````````````````````````` example
 * a
   > b
   >
 * c
 .
 <ul>
 <li>a
 <blockquote>
 <p>b</p>
 </blockquote>
 </li>
 <li>c</li>
 </ul>
 ````````````````````````````````
 
 
 This list is tight, because the consecutive block elements
 are not separated by blank lines:
 
 ```````````````````````````````` example
 - a
   > b
   ```
   c
   ```
 - d
 .
 <ul>
 <li>a
 <blockquote>
 <p>b</p>
 </blockquote>
 <pre><code>c
 </code></pre>
 </li>
 <li>d</li>
 </ul>
 ````````````````````````````````
 
 
 A single-paragraph list is tight:
 
 ```````````````````````````````` example
 - a
 .
 <ul>
 <li>a</li>
 </ul>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 - a
   - b
 .
 <ul>
 <li>a
 <ul>
 <li>b</li>
 </ul>
 </li>
 </ul>
 ````````````````````````````````
 
 
 This list is loose, because of the blank line between the
 two block elements in the list item:
 
 ```````````````````````````````` example
 1. ```
    foo
    ```
 
    bar
 .
 <ol>
 <li>
 <pre><code>foo
 </code></pre>
 <p>bar</p>
 </li>
 </ol>
 ````````````````````````````````
 
 
 Here the outer list is loose, the inner list tight:
 
 ```````````````````````````````` example
 * foo
   * bar
 
   baz
 .
 <ul>
 <li>
 <p>foo</p>
 <ul>
 <li>bar</li>
 </ul>
 <p>baz</p>
 </li>
 </ul>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 - a
   - b
   - c
 
 - d
   - e
   - f
 .
 <ul>
 <li>
 <p>a</p>
 <ul>
 <li>b</li>
 <li>c</li>
 </ul>
 </li>
 <li>
 <p>d</p>
 <ul>
 <li>e</li>
 <li>f</li>
 </ul>
 </li>
 </ul>
 ````````````````````````````````
 
 
 # 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`
 .
 <p><code>hi</code>lo`</p>
 ````````````````````````````````
 
 
 `hi` is parsed as code, leaving the backtick at the end as a literal
 backtick.
 
 ## Backslash escapes
 
 Any ASCII punctuation character may be backslash-escaped:
 
 ```````````````````````````````` example
 \!\"\#\$\%\&\'\(\)\*\+\,\-\.\/\:\;\<\=\>\?\@\[\\\]\^\_\`\{\|\}\~
 .
 <p>!&quot;#$%&amp;'()*+,-./:;&lt;=&gt;?@[\]^_`{|}~</p>
 ````````````````````````````````
 
 
 Backslashes before other characters are treated as literal
 backslashes:
 
 ```````````````````````````````` example
 \→\A\a\ \3\φ\«
 .
 <p>\→\A\a\ \3\φ\«</p>
 ````````````````````````````````
 
 
 Escaped characters are treated as regular characters and do
 not have their usual Markdown meanings:
 
 ```````````````````````````````` example
 \*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"
 .
 <p>*not emphasized*
 &lt;br/&gt; not a tag
 [not a link](/foo)
 `not code`
 1. not a list
 * not a list
 # not a heading
 [foo]: /url &quot;not a reference&quot;</p>
 ````````````````````````````````
 
 
 If a backslash is itself escaped, the following character is not:
 
 ```````````````````````````````` example
 \\*emphasis*
 .
 <p>\<em>emphasis</em></p>
 ````````````````````````````````
 
 
 A backslash at the end of the line is a [hard line break]:
 
 ```````````````````````````````` example
 foo\
 bar
 .
 <p>foo<br />
 bar</p>
 ````````````````````````````````
 
 
 Backslash escapes do not work in code blocks, code spans, autolinks, or
 raw HTML:
 
 ```````````````````````````````` example
 `` \[\` ``
 .
 <p><code>\[\`</code></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
     \[\]
 .
 <pre><code>\[\]
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ~~~
 \[\]
 ~~~
 .
 <pre><code>\[\]
 </code></pre>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <http://example.com?find=\*>
 .
 <p><a href="http://example.com?find=%5C*">http://example.com?find=\*</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <a href="/bar\/)">
 .
 <a href="/bar\/)">
 ````````````````````````````````
 
 
 But they work in all other contexts, including URLs and link titles,
 link references, and [info strings] in [fenced code blocks]:
 
 ```````````````````````````````` example
 [foo](/bar\* "ti\*tle")
 .
 <p><a href="/bar*" title="ti*tle">foo</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo]
 
 [foo]: /bar\* "ti\*tle"
 .
 <p><a href="/bar*" title="ti*tle">foo</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ``` foo\+bar
 foo
 ```
 .
 <pre><code class="language-foo+bar">foo
 </code></pre>
 ````````````````````````````````
 
 
 
 ## Entity and numeric character references
 
 All valid HTML entity references and numeric character
 references, except those occuring in code blocks and code spans,
 are recognized as such and treated as equivalent to the
 corresponding Unicode characters.  Conforming CommonMark parsers
 need not store information about whether a particular character
 was represented in the source using a Unicode character or
 an entity reference.
 
 [Entity references](@) consist of `&` + any of the valid
 HTML5 entity names + `;`. The
 document <https://html.spec.whatwg.org/multipage/entities.json>
 is used as an authoritative source for the valid entity
 references and their corresponding code points.
 
 ```````````````````````````````` example
 &nbsp; &amp; &copy; &AElig; &Dcaron;
 &frac34; &HilbertSpace; &DifferentialD;
 &ClockwiseContourIntegral; &ngE;
 .
 <p>  &amp; © Æ Ď
 ¾ ℋ ⅆ
 ∲ ≧̸</p>
 ````````````````````````````````
 
 
 [Decimal numeric character
 references](@)
 consist of `&#` + a string of 1--8 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
 &#35; &#1234; &#992; &#98765432; &#0;
 .
 <p># Ӓ Ϡ � �</p>
 ````````````````````````````````
 
 
 [Hexadecimal numeric character
 references](@) consist of `&#` +
 either `X` or `x` + a string of 1-8 hexadecimal digits + `;`.
 They too are parsed as the corresponding Unicode character (this
 time specified with a hexadecimal numeral instead of decimal).
 
 ```````````````````````````````` example
 &#X22; &#XD06; &#xcab;
 .
 <p>&quot; ആ ಫ</p>
 ````````````````````````````````
 
 
 Here are some nonentities:
 
 ```````````````````````````````` example
 &nbsp &x; &#; &#x;
 &ThisIsNotDefined; &hi?;
 .
 <p>&amp;nbsp &amp;x; &amp;#; &amp;#x;
 &amp;ThisIsNotDefined; &amp;hi?;</p>
 ````````````````````````````````
 
 
 Although HTML5 does accept some entity references
 without a trailing semicolon (such as `&copy`), these are not
 recognized here, because it makes the grammar too ambiguous:
 
 ```````````````````````````````` example
 &copy
 .
 <p>&amp;copy</p>
 ````````````````````````````````
 
 
 Strings that are not on the list of HTML5 named entities are not
 recognized as entity references either:
 
 ```````````````````````````````` example
 &MadeUpEntity;
 .
 <p>&amp;MadeUpEntity;</p>
 ````````````````````````````````
 
 
 Entity and numeric character references are recognized in any
 context besides code spans or code blocks, including
 URLs, [link titles], and [fenced code block][] [info strings]:
 
 ```````````````````````````````` example
 <a href="&ouml;&ouml;.html">
 .
 <a href="&ouml;&ouml;.html">
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo](/f&ouml;&ouml; "f&ouml;&ouml;")
 .
 <p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo]
 
 [foo]: /f&ouml;&ouml; "f&ouml;&ouml;"
 .
 <p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ``` f&ouml;&ouml;
 foo
 ```
 .
 <pre><code class="language-föö">foo
 </code></pre>
 ````````````````````````````````
 
 
 Entity and numeric character references are treated as literal
 text in code spans and code blocks:
 
 ```````````````````````````````` example
 `f&ouml;&ouml;`
 .
 <p><code>f&amp;ouml;&amp;ouml;</code></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
     f&ouml;f&ouml;
 .
 <pre><code>f&amp;ouml;f&amp;ouml;
 </code></pre>
 ````````````````````````````````
 
 
 ## 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 the two backtick strings, with leading and
 trailing spaces and [line endings] removed, and
 [whitespace] collapsed to single spaces.
 
 This is a simple code span:
 
 ```````````````````````````````` example
 `foo`
 .
 <p><code>foo</code></p>
 ````````````````````````````````
 
 
 Here two backticks are used, because the code contains a backtick.
 This example also illustrates stripping of leading and trailing spaces:
 
 ```````````````````````````````` example
 `` foo ` bar  ``
 .
 <p><code>foo ` bar</code></p>
 ````````````````````````````````
 
 
 This example shows the motivation for stripping leading and trailing
 spaces:
 
 ```````````````````````````````` example
 ` `` `
 .
 <p><code>``</code></p>
 ````````````````````````````````
 
 
 [Line endings] are treated like spaces:
 
 ```````````````````````````````` example
 ``
 foo
 ``
 .
 <p><code>foo</code></p>
 ````````````````````````````````
 
 
 Interior spaces and [line endings] are collapsed into
 single spaces, just as they would be by a browser:
 
 ```````````````````````````````` example
 `foo   bar
   baz`
 .
 <p><code>foo bar baz</code></p>
 ````````````````````````````````
 
 
 Not all [Unicode whitespace] (for instance, non-breaking space) is
 collapsed, however:
 
 ```````````````````````````````` example
 `a  b`
 .
 <p><code>a  b</code></p>
 ````````````````````````````````
 
 
 Q: Why not just leave the spaces, since browsers will collapse them
 anyway?  A:  Because we might be targeting a non-HTML format, and we
 shouldn't rely on HTML-specific rendering assumptions.
 
 (Existing implementations differ in their treatment of internal
 spaces and [line endings].  Some, including `Markdown.pl` and
 `showdown`, convert an internal [line ending] into a
 `<br />` tag.  But this makes things difficult for those who like to
 hard-wrap their paragraphs, since a line break in the midst of a code
 span will cause an unintended line break in the output.  Others just
 leave internal spaces as they are, which is fine if only HTML is being
 targeted.)
 
 ```````````````````````````````` example
 `foo `` bar`
 .
 <p><code>foo `` bar</code></p>
 ````````````````````````````````
 
 
 Note that backslash escapes do not work in code spans. All backslashes
 are treated literally:
 
 ```````````````````````````````` example
 `foo\`bar`
 .
 <p><code>foo\</code>bar`</p>
 ````````````````````````````````
 
 
 Backslash escapes are never needed, because one can always choose a
 string of *n* backtick characters as delimiters, where the code does
 not contain any strings of exactly *n* backtick characters.
 
 Code span backticks have higher precedence than any other inline
 constructs except HTML tags and autolinks.  Thus, for example, this is
 not parsed as emphasized text, since the second `*` is part of a code
 span:
 
 ```````````````````````````````` example
 *foo`*`
 .
 <p>*foo<code>*</code></p>
 ````````````````````````````````
 
 
 And this is not parsed as a link:
 
 ```````````````````````````````` example
 [not a `link](/foo`)
 .
 <p>[not a <code>link](/foo</code>)</p>
 ````````````````````````````````
 
 
 Code spans, HTML tags, and autolinks have the same precedence.
 Thus, this is code:
 
 ```````````````````````````````` example
 `<a href="`">`
 .
 <p><code>&lt;a href=&quot;</code>&quot;&gt;`</p>
 ````````````````````````````````
 
 
 But this is an HTML tag:
 
 ```````````````````````````````` example
 <a href="`">`
 .
 <p><a href="`">`</p>
 ````````````````````````````````
 
 
 And this is code:
 
 ```````````````````````````````` example
 `<http://foo.bar.`baz>`
 .
 <p><code>&lt;http://foo.bar.</code>baz&gt;`</p>
 ````````````````````````````````
 
 
 But this is an autolink:
 
 ```````````````````````````````` example
 <http://foo.bar.`baz>`
 .
 <p><a href="http://foo.bar.%60baz">http://foo.bar.`baz</a>`</p>
 ````````````````````````````````
 
 
 When a backtick string is not closed by a matching backtick string,
 we just have literal backticks:
 
 ```````````````````````````````` example
 ```foo``
 .
 <p>```foo``</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 `foo
 .
 <p>`foo</p>
 ````````````````````````````````
 
 The following case also illustrates the need for opening and
 closing backtick strings to be equal in length:
 
 ```````````````````````````````` example
 `foo``bar``
 .
 <p>`foo<code>bar</code></p>
 ````````````````````````````````
 
 
 ## Emphasis and strong emphasis
 
 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
 > `<em>` tag; double `*`'s or `_`'s will be wrapped with an HTML `<strong>`
 > tag.
 
 This is enough for most users, but these rules leave much undecided,
 especially when it comes to nested emphasis.  The original
 `Markdown.pl` test suite makes it clear that triple `***` and
 `___` delimiters can be used for strong emphasis, and most
 implementations have also allowed the following patterns:
 
 ``` 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 `*` character, or a sequence of one or more `_`
 characters that is not preceded or followed by a `_` character.
 
 A [left-flanking delimiter run](@) is
 a [delimiter run] that is (a) not followed by [Unicode whitespace],
 and (b) not followed by a [punctuation character], or
 preceded by [Unicode whitespace] or a [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 (a) not preceded by [Unicode whitespace],
 and (b) not preceded by a [punctuation character], or
 followed by [Unicode whitespace] or a [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 punctuation.
 
 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 punctuation.
 
 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 punctuation.
 
 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 punctuation.
 
 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.
 
 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.
 
 11. A literal `*` character cannot occur at the beginning or end of
     `*`-delimited emphasis or `**`-delimited strong emphasis, unless it
     is backslash-escaped.
 
 12. A literal `_` character cannot occur at the beginning or end of
     `_`-delimited emphasis or `__`-delimited strong emphasis, unless it
     is backslash-escaped.
 
 Where rules 1--12 above are compatible with multiple parsings,
 the following principles resolve ambiguity:
 
 13. The number of nestings should be minimized. Thus, for example,
     an interpretation `<strong>...</strong>` is always preferred to
     `<em><em>...</em></em>`.
 
 14. An interpretation `<em><strong>...</strong></em>` is always
     preferred to `<strong><em>...</em></strong>`.
 
 15. When two potential emphasis or strong emphasis spans overlap,
     so that the second begins before the first ends and ends after
     the first ends, the first takes precedence. Thus, for example,
     `*foo _bar* baz_` is parsed as `<em>foo _bar</em> baz_` rather
     than `*foo <em>bar* baz</em>`.
 
 16. When there are two potential emphasis or strong emphasis spans
     with the same closing delimiter, the shorter one (the one that
     opens later) takes precedence. Thus, for example,
     `**foo **bar baz**` is parsed as `**foo <strong>bar baz</strong>`
     rather than `<strong>foo **bar baz</strong>`.
 
 17. Inline code spans, links, images, and HTML tags group more tightly
     than emphasis.  So, when there is a choice between an interpretation
     that contains one of these elements and one that does not, the
     former always wins.  Thus, for example, `*[foo*](bar)` is
     parsed as `*<a href="bar">foo*</a>` rather than as
     `<em>[foo</em>](bar)`.
 
 These rules can be illustrated through a series of examples.
 
 Rule 1:
 
 ```````````````````````````````` example
 *foo bar*
 .
 <p><em>foo bar</em></p>
 ````````````````````````````````
 
 
 This is not emphasis, because the opening `*` is followed by
 whitespace, and hence not part of a [left-flanking delimiter run]:
 
 ```````````````````````````````` example
 a * foo bar*
 .
 <p>a * foo bar*</p>
 ````````````````````````````````
 
 
 This is not emphasis, because the opening `*` is preceded
 by an alphanumeric and followed by punctuation, and hence
 not part of a [left-flanking delimiter run]:
 
 ```````````````````````````````` example
 a*"foo"*
 .
 <p>a*&quot;foo&quot;*</p>
 ````````````````````````````````
 
 
 Unicode nonbreaking spaces count as whitespace, too:
 
 ```````````````````````````````` example
 * a *
 .
 <p>* a *</p>
 ````````````````````````````````
 
 
 Intraword emphasis with `*` is permitted:
 
 ```````````````````````````````` example
 foo*bar*
 .
 <p>foo<em>bar</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 5*6*78
 .
 <p>5<em>6</em>78</p>
 ````````````````````````````````
 
 
 Rule 2:
 
 ```````````````````````````````` example
 _foo bar_
 .
 <p><em>foo bar</em></p>
 ````````````````````````````````
 
 
 This is not emphasis, because the opening `_` is followed by
 whitespace:
 
 ```````````````````````````````` example
 _ foo bar_
 .
 <p>_ foo bar_</p>
 ````````````````````````````````
 
 
 This is not emphasis, because the opening `_` is preceded
 by an alphanumeric and followed by punctuation:
 
 ```````````````````````````````` example
 a_"foo"_
 .
 <p>a_&quot;foo&quot;_</p>
 ````````````````````````````````
 
 
 Emphasis with `_` is not allowed inside words:
 
 ```````````````````````````````` example
 foo_bar_
 .
 <p>foo_bar_</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 5_6_78
 .
 <p>5_6_78</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 пристаням_стремятся_
 .
 <p>пристаням_стремятся_</p>
 ````````````````````````````````
 
 
 Here `_` does not generate emphasis, because the first delimiter run
 is right-flanking and the second left-flanking:
 
 ```````````````````````````````` example
 aa_"bb"_cc
 .
 <p>aa_&quot;bb&quot;_cc</p>
 ````````````````````````````````
 
 
 This is emphasis, even though the opening delimiter is
 both left- and right-flanking, because it is preceded by
 punctuation:
 
 ```````````````````````````````` example
 foo-_(bar)_
 .
 <p>foo-<em>(bar)</em></p>
 ````````````````````````````````
 
 
 Rule 3:
 
 This is not emphasis, because the closing delimiter does
 not match the opening delimiter:
 
 ```````````````````````````````` example
 _foo*
 .
 <p>_foo*</p>
 ````````````````````````````````
 
 
 This is not emphasis, because the closing `*` is preceded by
 whitespace:
 
 ```````````````````````````````` example
 *foo bar *
 .
 <p>*foo bar *</p>
 ````````````````````````````````
 
 
 A newline also counts as whitespace:
 
 ```````````````````````````````` example
 *foo bar
 *
 .
 <p>*foo bar
 *</p>
 ````````````````````````````````
 
 
 This is not emphasis, because the second `*` is
 preceded by punctuation and followed by an alphanumeric
 (hence it is not part of a [right-flanking delimiter run]:
 
 ```````````````````````````````` example
 *(*foo)
 .
 <p>*(*foo)</p>
 ````````````````````````````````
 
 
 The point of this restriction is more easily appreciated
 with this example:
 
 ```````````````````````````````` example
 *(*foo*)*
 .
 <p><em>(<em>foo</em>)</em></p>
 ````````````````````````````````
 
 
 Intraword emphasis with `*` is allowed:
 
 ```````````````````````````````` example
 *foo*bar
 .
 <p><em>foo</em>bar</p>
 ````````````````````````````````
 
 
 
 Rule 4:
 
 This is not emphasis, because the closing `_` is preceded by
 whitespace:
 
 ```````````````````````````````` example
 _foo bar _
 .
 <p>_foo bar _</p>
 ````````````````````````````````
 
 
 This is not emphasis, because the second `_` is
 preceded by punctuation and followed by an alphanumeric:
 
 ```````````````````````````````` example
 _(_foo)
 .
 <p>_(_foo)</p>
 ````````````````````````````````
 
 
 This is emphasis within emphasis:
 
 ```````````````````````````````` example
 _(_foo_)_
 .
 <p><em>(<em>foo</em>)</em></p>
 ````````````````````````````````
 
 
 Intraword emphasis is disallowed for `_`:
 
 ```````````````````````````````` example
 _foo_bar
 .
 <p>_foo_bar</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 _пристаням_стремятся
 .
 <p>_пристаням_стремятся</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 _foo_bar_baz_
 .
 <p><em>foo_bar_baz</em></p>
 ````````````````````````````````
 
 
 This is emphasis, even though the closing delimiter is
 both left- and right-flanking, because it is followed by
 punctuation:
 
 ```````````````````````````````` example
 _(bar)_.
 .
 <p><em>(bar)</em>.</p>
 ````````````````````````````````
 
 
 Rule 5:
 
 ```````````````````````````````` example
 **foo bar**
 .
 <p><strong>foo bar</strong></p>
 ````````````````````````````````
 
 
 This is not strong emphasis, because the opening delimiter is
 followed by whitespace:
 
 ```````````````````````````````` example
 ** foo bar**
 .
 <p>** foo bar**</p>
 ````````````````````````````````
 
 
 This is not strong emphasis, because the opening `**` is preceded
 by an alphanumeric and followed by punctuation, and hence
 not part of a [left-flanking delimiter run]:
 
 ```````````````````````````````` example
 a**"foo"**
 .
 <p>a**&quot;foo&quot;**</p>
 ````````````````````````````````
 
 
 Intraword strong emphasis with `**` is permitted:
 
 ```````````````````````````````` example
 foo**bar**
 .
 <p>foo<strong>bar</strong></p>
 ````````````````````````````````
 
 
 Rule 6:
 
 ```````````````````````````````` example
 __foo bar__
 .
 <p><strong>foo bar</strong></p>
 ````````````````````````````````
 
 
 This is not strong emphasis, because the opening delimiter is
 followed by whitespace:
 
 ```````````````````````````````` example
 __ foo bar__
 .
 <p>__ foo bar__</p>
 ````````````````````````````````
 
 
 A newline counts as whitespace:
 ```````````````````````````````` example
 __
 foo bar__
 .
 <p>__
 foo bar__</p>
 ````````````````````````````````
 
 
 This is not strong emphasis, because the opening `__` is preceded
 by an alphanumeric and followed by punctuation:
 
 ```````````````````````````````` example
 a__"foo"__
 .
 <p>a__&quot;foo&quot;__</p>
 ````````````````````````````````
 
 
 Intraword strong emphasis is forbidden with `__`:
 
 ```````````````````````````````` example
 foo__bar__
 .
 <p>foo__bar__</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 5__6__78
 .
 <p>5__6__78</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 пристаням__стремятся__
 .
 <p>пристаням__стремятся__</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 __foo, __bar__, baz__
 .
 <p><strong>foo, <strong>bar</strong>, baz</strong></p>
 ````````````````````````````````
 
 
 This is strong emphasis, even though the opening delimiter is
 both left- and right-flanking, because it is preceded by
 punctuation:
 
 ```````````````````````````````` example
 foo-__(bar)__
 .
 <p>foo-<strong>(bar)</strong></p>
 ````````````````````````````````
 
 
 
 Rule 7:
 
 This is not strong emphasis, because the closing delimiter is preceded
 by whitespace:
 
 ```````````````````````````````` example
 **foo bar **
 .
 <p>**foo bar **</p>
 ````````````````````````````````
 
 
 (Nor can it be interpreted as an emphasized `*foo bar *`, because of
 Rule 11.)
 
 This is not strong emphasis, because the second `**` is
 preceded by punctuation and followed by an alphanumeric:
 
 ```````````````````````````````` example
 **(**foo)
 .
 <p>**(**foo)</p>
 ````````````````````````````````
 
 
 The point of this restriction is more easily appreciated
 with these examples:
 
 ```````````````````````````````` example
 *(**foo**)*
 .
 <p><em>(<strong>foo</strong>)</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **Gomphocarpus (*Gomphocarpus physocarpus*, syn.
 *Asclepias physocarpa*)**
 .
 <p><strong>Gomphocarpus (<em>Gomphocarpus physocarpus</em>, syn.
 <em>Asclepias physocarpa</em>)</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **foo "*bar*" foo**
 .
 <p><strong>foo &quot;<em>bar</em>&quot; foo</strong></p>
 ````````````````````````````````
 
 
 Intraword emphasis:
 
 ```````````````````````````````` example
 **foo**bar
 .
 <p><strong>foo</strong>bar</p>
 ````````````````````````````````
 
 
 Rule 8:
 
 This is not strong emphasis, because the closing delimiter is
 preceded by whitespace:
 
 ```````````````````````````````` example
 __foo bar __
 .
 <p>__foo bar __</p>
 ````````````````````````````````
 
 
 This is not strong emphasis, because the second `__` is
 preceded by punctuation and followed by an alphanumeric:
 
 ```````````````````````````````` example
 __(__foo)
 .
 <p>__(__foo)</p>
 ````````````````````````````````
 
 
 The point of this restriction is more easily appreciated
 with this example:
 
 ```````````````````````````````` example
 _(__foo__)_
 .
 <p><em>(<strong>foo</strong>)</em></p>
 ````````````````````````````````
 
 
 Intraword strong emphasis is forbidden with `__`:
 
 ```````````````````````````````` example
 __foo__bar
 .
 <p>__foo__bar</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 __пристаням__стремятся
 .
 <p>__пристаням__стремятся</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 __foo__bar__baz__
 .
 <p><strong>foo__bar__baz</strong></p>
 ````````````````````````````````
 
 
 This is strong emphasis, even though the closing delimiter is
 both left- and right-flanking, because it is followed by
 punctuation:
 
 ```````````````````````````````` example
 __(bar)__.
 .
 <p><strong>(bar)</strong>.</p>
 ````````````````````````````````
 
 
 Rule 9:
 
 Any nonempty sequence of inline elements can be the contents of an
 emphasized span.
 
 ```````````````````````````````` example
 *foo [bar](/url)*
 .
 <p><em>foo <a href="/url">bar</a></em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *foo
 bar*
 .
 <p><em>foo
 bar</em></p>
 ````````````````````````````````
 
 
 In particular, emphasis and strong emphasis can be nested
 inside emphasis:
 
 ```````````````````````````````` example
 _foo __bar__ baz_
 .
 <p><em>foo <strong>bar</strong> baz</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 _foo _bar_ baz_
 .
 <p><em>foo <em>bar</em> baz</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 __foo_ bar_
 .
 <p><em><em>foo</em> bar</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *foo *bar**
 .
 <p><em>foo <em>bar</em></em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *foo **bar** baz*
 .
 <p><em>foo <strong>bar</strong> baz</em></p>
 ````````````````````````````````
 
 ```````````````````````````````` example
 *foo**bar**baz*
 .
 <p><em>foo<strong>bar</strong>baz</em></p>
 ````````````````````````````````
 
 Note that in the preceding case, the interpretation
 
 ``` markdown
 <p><em>foo</em><em>bar<em></em>baz</em></p>
 ```
 
 
 is precluded by the condition that a delimiter that
 can both open and close (like the `*` after `foo`)
 cannot form emphasis if the sum of the lengths of
 the delimiter runs containing the opening and
 closing delimiters is a multiple of 3.
 
 The same condition ensures that the following
 cases are all strong emphasis nested inside
 emphasis, even when the interior spaces are
 omitted:
 
 
 ```````````````````````````````` example
 ***foo** bar*
 .
 <p><em><strong>foo</strong> bar</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *foo **bar***
 .
 <p><em>foo <strong>bar</strong></em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *foo**bar***
 .
 <p><em>foo<strong>bar</strong></em></p>
 ````````````````````````````````
 
 
 Indefinite levels of nesting are possible:
 
 ```````````````````````````````` example
 *foo **bar *baz* bim** bop*
 .
 <p><em>foo <strong>bar <em>baz</em> bim</strong> bop</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *foo [*bar*](/url)*
 .
 <p><em>foo <a href="/url"><em>bar</em></a></em></p>
 ````````````````````````````````
 
 
 There can be no empty emphasis or strong emphasis:
 
 ```````````````````````````````` example
 ** is not an empty emphasis
 .
 <p>** is not an empty emphasis</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **** is not an empty strong emphasis
 .
 <p>**** is not an empty strong emphasis</p>
 ````````````````````````````````
 
 
 
 Rule 10:
 
 Any nonempty sequence of inline elements can be the contents of an
 strongly emphasized span.
 
 ```````````````````````````````` example
 **foo [bar](/url)**
 .
 <p><strong>foo <a href="/url">bar</a></strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **foo
 bar**
 .
 <p><strong>foo
 bar</strong></p>
 ````````````````````````````````
 
 
 In particular, emphasis and strong emphasis can be nested
 inside strong emphasis:
 
 ```````````````````````````````` example
 __foo _bar_ baz__
 .
 <p><strong>foo <em>bar</em> baz</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 __foo __bar__ baz__
 .
 <p><strong>foo <strong>bar</strong> baz</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ____foo__ bar__
 .
 <p><strong><strong>foo</strong> bar</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **foo **bar****
 .
 <p><strong>foo <strong>bar</strong></strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **foo *bar* baz**
 .
 <p><strong>foo <em>bar</em> baz</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **foo*bar*baz**
 .
 <p><strong>foo<em>bar</em>baz</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ***foo* bar**
 .
 <p><strong><em>foo</em> bar</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **foo *bar***
 .
 <p><strong>foo <em>bar</em></strong></p>
 ````````````````````````````````
 
 
 Indefinite levels of nesting are possible:
 
 ```````````````````````````````` example
 **foo *bar **baz**
 bim* bop**
 .
 <p><strong>foo <em>bar <strong>baz</strong>
 bim</em> bop</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **foo [*bar*](/url)**
 .
 <p><strong>foo <a href="/url"><em>bar</em></a></strong></p>
 ````````````````````````````````
 
 
 There can be no empty emphasis or strong emphasis:
 
 ```````````````````````````````` example
 __ is not an empty emphasis
 .
 <p>__ is not an empty emphasis</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ____ is not an empty strong emphasis
 .
 <p>____ is not an empty strong emphasis</p>
 ````````````````````````````````
 
 
 
 Rule 11:
 
 ```````````````````````````````` example
 foo ***
 .
 <p>foo ***</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo *\**
 .
 <p>foo <em>*</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo *_*
 .
 <p>foo <em>_</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo *****
 .
 <p>foo *****</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo **\***
 .
 <p>foo <strong>*</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo **_**
 .
 <p>foo <strong>_</strong></p>
 ````````````````````````````````
 
 
 Note that when delimiters do not match evenly, Rule 11 determines
 that the excess literal `*` characters will appear outside of the
 emphasis, rather than inside it:
 
 ```````````````````````````````` example
 **foo*
 .
 <p>*<em>foo</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *foo**
 .
 <p><em>foo</em>*</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ***foo**
 .
 <p>*<strong>foo</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ****foo*
 .
 <p>***<em>foo</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **foo***
 .
 <p><strong>foo</strong>*</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *foo****
 .
 <p><em>foo</em>***</p>
 ````````````````````````````````
 
 
 
 Rule 12:
 
 ```````````````````````````````` example
 foo ___
 .
 <p>foo ___</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo _\__
 .
 <p>foo <em>_</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo _*_
 .
 <p>foo <em>*</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo _____
 .
 <p>foo _____</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo __\___
 .
 <p>foo <strong>_</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo __*__
 .
 <p>foo <strong>*</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 __foo_
 .
 <p>_<em>foo</em></p>
 ````````````````````````````````
 
 
 Note that when delimiters do not match evenly, Rule 12 determines
 that the excess literal `_` characters will appear outside of the
 emphasis, rather than inside it:
 
 ```````````````````````````````` example
 _foo__
 .
 <p><em>foo</em>_</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ___foo__
 .
 <p>_<strong>foo</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ____foo_
 .
 <p>___<em>foo</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 __foo___
 .
 <p><strong>foo</strong>_</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 _foo____
 .
 <p><em>foo</em>___</p>
 ````````````````````````````````
 
 
 Rule 13 implies that if you want emphasis nested directly inside
 emphasis, you must use different delimiters:
 
 ```````````````````````````````` example
 **foo**
 .
 <p><strong>foo</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *_foo_*
 .
 <p><em><em>foo</em></em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 __foo__
 .
 <p><strong>foo</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 _*foo*_
 .
 <p><em><em>foo</em></em></p>
 ````````````````````````````````
 
 
 However, strong emphasis within strong emphasis is possible without
 switching delimiters:
 
 ```````````````````````````````` example
 ****foo****
 .
 <p><strong><strong>foo</strong></strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ____foo____
 .
 <p><strong><strong>foo</strong></strong></p>
 ````````````````````````````````
 
 
 
 Rule 13 can be applied to arbitrarily long sequences of
 delimiters:
 
 ```````````````````````````````` example
 ******foo******
 .
 <p><strong><strong><strong>foo</strong></strong></strong></p>
 ````````````````````````````````
 
 
 Rule 14:
 
 ```````````````````````````````` example
 ***foo***
 .
 <p><em><strong>foo</strong></em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 _____foo_____
 .
 <p><em><strong><strong>foo</strong></strong></em></p>
 ````````````````````````````````
 
 
 Rule 15:
 
 ```````````````````````````````` example
 *foo _bar* baz_
 .
 <p><em>foo _bar</em> baz_</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *foo __bar *baz bim__ bam*
 .
 <p><em>foo <strong>bar *baz bim</strong> bam</em></p>
 ````````````````````````````````
 
 
 Rule 16:
 
 ```````````````````````````````` example
 **foo **bar baz**
 .
 <p>**foo <strong>bar baz</strong></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *foo *bar baz*
 .
 <p>*foo <em>bar baz</em></p>
 ````````````````````````````````
 
 
 Rule 17:
 
 ```````````````````````````````` example
 *[bar*](/url)
 .
 <p>*<a href="/url">bar*</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 _foo [bar_](/url)
 .
 <p>_foo <a href="/url">bar_</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *<img src="foo" title="*"/>
 .
 <p>*<img src="foo" title="*"/></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **<a href="**">
 .
 <p>**<a href="**"></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 __<a href="__">
 .
 <p>__<a href="__"></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *a `*`*
 .
 <p><em>a <code>*</code></em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 _a `_`_
 .
 <p><em>a <code>_</code></em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 **a<http://foo.bar/?q=**>
 .
 <p>**a<a href="http://foo.bar/?q=**">http://foo.bar/?q=**</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 __a<http://foo.bar/?q=__>
 .
 <p>__a<a href="http://foo.bar/?q=__">http://foo.bar/?q=__</a></p>
 ````````````````````````````````
 
 
 
 ## 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 spaces, line breaks, or unescaped
   `<` or `>` characters, or
 
 - a nonempty sequence of characters that does not include
   ASCII space or control characters, and includes parentheses
   only if (a) they are backslash-escaped or (b) they are part of
   a balanced pair of unescaped parentheses.
 
 A [link title](@)  consists of either
 
 - a sequence of zero or more characters between straight double-quote
   characters (`"`), including a `"` character only if it is
   backslash-escaped, or
 
 - a sequence of zero or more characters between straight single-quote
   characters (`'`), including a `'` character only if it is
   backslash-escaped, or
 
 - a sequence of zero or more characters between matching parentheses
   (`(...)`), including a `)` character only if it is backslash-escaped.
 
 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 `(`, optional [whitespace], an optional
 [link destination], an optional [link title] separated from the link
 destination by [whitespace], optional [whitespace], and a right
 parenthesis `)`. The link's text consists of the inlines contained
 in the [link text] (excluding the enclosing square brackets).
 The link's URI consists of the link destination, excluding enclosing
 `<...>` if present, with backslash-escapes in effect as described
 above.  The link's title consists of the link title, excluding its
 enclosing delimiters, with backslash-escapes in effect as described
 above.
 
 Here is a simple inline link:
 
 ```````````````````````````````` example
 [link](/uri "title")
 .
 <p><a href="/uri" title="title">link</a></p>
 ````````````````````````````````
 
 
 The title may be omitted:
 
 ```````````````````````````````` example
 [link](/uri)
 .
 <p><a href="/uri">link</a></p>
 ````````````````````````````````
 
 
 Both the title and the destination may be omitted:
 
 ```````````````````````````````` example
 [link]()
 .
 <p><a href="">link</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [link](<>)
 .
 <p><a href="">link</a></p>
 ````````````````````````````````
 
 
 The destination cannot contain spaces or line breaks,
 even if enclosed in pointy brackets:
 
 ```````````````````````````````` example
 [link](/my uri)
 .
 <p>[link](/my uri)</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [link](</my uri>)
 .
 <p>[link](&lt;/my uri&gt;)</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [link](foo
 bar)
 .
 <p>[link](foo
 bar)</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [link](<foo
 bar>)
 .
 <p>[link](<foo
 bar>)</p>
 ````````````````````````````````
 
 Parentheses inside the link destination may be escaped:
 
 ```````````````````````````````` example
 [link](\(foo\))
 .
 <p><a href="(foo)">link</a></p>
 ````````````````````````````````
 
 Any number parentheses are allowed without escaping, as long as they are
 balanced:
 
 ```````````````````````````````` example
 [link](foo(and(bar)))
 .
 <p><a href="foo(and(bar))">link</a></p>
 ````````````````````````````````
 
 However, if you have unbalanced parentheses, you need to escape or use the
 `<...>` form:
 
 ```````````````````````````````` example
 [link](foo\(and\(bar\))
 .
 <p><a href="foo(and(bar)">link</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [link](<foo(and(bar)>)
 .
 <p><a href="foo(and(bar)">link</a></p>
 ````````````````````````````````
 
 
 Parentheses and other symbols can also be escaped, as usual
 in Markdown:
 
 ```````````````````````````````` example
 [link](foo\)\:)
 .
 <p><a href="foo):">link</a></p>
 ````````````````````````````````
 
 
 A link can contain fragment identifiers and queries:
 
 ```````````````````````````````` example
 [link](#fragment)
 
 [link](http://example.com#fragment)
 
 [link](http://example.com?foo=3#frag)
 .
 <p><a href="#fragment">link</a></p>
 <p><a href="http://example.com#fragment">link</a></p>
 <p><a href="http://example.com?foo=3#frag">link</a></p>
 ````````````````````````````````
 
 
 Note that a backslash before a non-escapable character is
 just a backslash:
 
 ```````````````````````````````` example
 [link](foo\bar)
 .
 <p><a href="foo%5Cbar">link</a></p>
 ````````````````````````````````
 
 
 URL-escaping should be left alone inside the destination, as all
 URL-escaped characters are also valid URL characters. Entity and
 numerical character references in the destination will be parsed
 into the corresponding Unicode code points, as usual.  These may
 be optionally URL-escaped when written as HTML, but this spec
 does not enforce any particular policy for rendering URLs in
 HTML or other formats.  Renderers may make different decisions
 about how to escape or normalize URLs in the output.
 
 ```````````````````````````````` example
 [link](foo%20b&auml;)
 .
 <p><a href="foo%20b%C3%A4">link</a></p>
 ````````````````````````````````
 
 
 Note that, because titles can often be parsed as destinations,
 if you try to omit the destination and keep the title, you'll
 get unexpected results:
 
 ```````````````````````````````` example
 [link]("title")
 .
 <p><a href="%22title%22">link</a></p>
 ````````````````````````````````
 
 
 Titles may be in single quotes, double quotes, or parentheses:
 
 ```````````````````````````````` example
 [link](/url "title")
 [link](/url 'title')
 [link](/url (title))
 .
 <p><a href="/url" title="title">link</a>
 <a href="/url" title="title">link</a>
 <a href="/url" title="title">link</a></p>
 ````````````````````````````````
 
 
 Backslash escapes and entity and numeric character references
 may be used in titles:
 
 ```````````````````````````````` example
 [link](/url "title \"&quot;")
 .
 <p><a href="/url" title="title &quot;&quot;">link</a></p>
 ````````````````````````````````
 
 
 Titles must be separated from the link using a [whitespace].
 Other [Unicode whitespace] like non-breaking space doesn't work.
 
 ```````````````````````````````` example
 [link](/url "title")
 .
 <p><a href="/url%C2%A0%22title%22">link</a></p>
 ````````````````````````````````
 
 
 Nested balanced quotes are not allowed without escaping:
 
 ```````````````````````````````` example
 [link](/url "title "and" title")
 .
 <p>[link](/url &quot;title &quot;and&quot; title&quot;)</p>
 ````````````````````````````````
 
 
 But it is easy to work around this by using a different quote type:
 
 ```````````````````````````````` example
 [link](/url 'title "and" title')
 .
 <p><a href="/url" title="title &quot;and&quot; title">link</a></p>
 ````````````````````````````````
 
 
 (Note:  `Markdown.pl` did allow double quotes inside a double-quoted
 title, and its test suite included a test demonstrating this.
 But it is hard to see a good rationale for the extra complexity this
 brings, since there are already many ways---backslash escaping,
 entity and numeric character references, or using a different
 quote type for the enclosing title---to write titles containing
 double quotes.  `Markdown.pl`'s handling of titles has a number
 of other strange features.  For example, it allows single-quoted
 titles in inline links, but not reference links.  And, in
 reference links but not inline links, it allows a title to begin
 with `"` and end with `)`.  `Markdown.pl` 1.0.1 even allows
 titles with no closing quotation mark, though 1.0.2b8 does not.
 It seems preferable to adopt a simple, rational rule that works
 the same way in inline links and link reference definitions.)
 
 [Whitespace] is allowed around the destination and title:
 
 ```````````````````````````````` example
 [link](   /uri
   "title"  )
 .
 <p><a href="/uri" title="title">link</a></p>
 ````````````````````````````````
 
 
 But it is not allowed between the link text and the
 following parenthesis:
 
 ```````````````````````````````` example
 [link] (/uri)
 .
 <p>[link] (/uri)</p>
 ````````````````````````````````
 
 
 The link text may contain balanced brackets, but not unbalanced ones,
 unless they are escaped:
 
 ```````````````````````````````` example
 [link [foo [bar]]](/uri)
 .
 <p><a href="/uri">link [foo [bar]]</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [link] bar](/uri)
 .
 <p>[link] bar](/uri)</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [link [bar](/uri)
 .
 <p>[link <a href="/uri">bar</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [link \[bar](/uri)
 .
 <p><a href="/uri">link [bar</a></p>
 ````````````````````````````````
 
 
 The link text may contain inline content:
 
 ```````````````````````````````` example
 [link *foo **bar** `#`*](/uri)
 .
 <p><a href="/uri">link <em>foo <strong>bar</strong> <code>#</code></em></a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [![moon](moon.jpg)](/uri)
 .
 <p><a href="/uri"><img src="moon.jpg" alt="moon" /></a></p>
 ````````````````````````````````
 
 
 However, links may not contain other links, at any level of nesting.
 
 ```````````````````````````````` example
 [foo [bar](/uri)](/uri)
 .
 <p>[foo <a href="/uri">bar</a>](/uri)</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo *[bar [baz](/uri)](/uri)*](/uri)
 .
 <p>[foo <em>[bar <a href="/uri">baz</a>](/uri)</em>](/uri)</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ![[[foo](uri1)](uri2)](uri3)
 .
 <p><img src="uri3" alt="[foo](uri2)" /></p>
 ````````````````````````````````
 
 
 These cases illustrate the precedence of link text grouping over
 emphasis grouping:
 
 ```````````````````````````````` example
 *[foo*](/uri)
 .
 <p>*<a href="/uri">foo*</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo *bar](baz*)
 .
 <p><a href="baz*">foo *bar</a></p>
 ````````````````````````````````
 
 
 Note that brackets that *aren't* part of links do not take
 precedence:
 
 ```````````````````````````````` example
 *foo [bar* baz]
 .
 <p><em>foo [bar</em> baz]</p>
 ````````````````````````````````
 
 
 These cases illustrate the precedence of HTML tags, code spans,
 and autolinks over link grouping:
 
 ```````````````````````````````` example
 [foo <bar attr="](baz)">
 .
 <p>[foo <bar attr="](baz)"></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo`](/uri)`
 .
 <p>[foo<code>](/uri)</code></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo<http://example.com/?search=](uri)>
 .
 <p>[foo<a href="http://example.com/?search=%5D(uri)">http://example.com/?search=](uri)</a></p>
 ````````````````````````````````
 
 
 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 [non-whitespace character].
 Unescaped square bracket characters are not allowed in
 [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, perform the *Unicode case fold* and collapse consecutive internal
 [whitespace] to a single space.  If there are multiple
 matching reference link definitions, the one that comes first in the
 document is used.  (It is desirable in such cases to emit a warning.)
 
 The contents of the first link label are parsed as inlines, which are
 used as the link's text.  The link's URI and title are provided by the
 matching [link reference definition].
 
 Here is a simple example:
 
 ```````````````````````````````` example
 [foo][bar]
 
 [bar]: /url "title"
 .
 <p><a href="/url" title="title">foo</a></p>
 ````````````````````````````````
 
 
 The rules for the [link text] are the same as with
 [inline links].  Thus:
 
 The link text may contain balanced brackets, but not unbalanced ones,
 unless they are escaped:
 
 ```````````````````````````````` example
 [link [foo [bar]]][ref]
 
 [ref]: /uri
 .
 <p><a href="/uri">link [foo [bar]]</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [link \[bar][ref]
 
 [ref]: /uri
 .
 <p><a href="/uri">link [bar</a></p>
 ````````````````````````````````
 
 
 The link text may contain inline content:
 
 ```````````````````````````````` example
 [link *foo **bar** `#`*][ref]
 
 [ref]: /uri
 .
 <p><a href="/uri">link <em>foo <strong>bar</strong> <code>#</code></em></a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [![moon](moon.jpg)][ref]
 
 [ref]: /uri
 .
 <p><a href="/uri"><img src="moon.jpg" alt="moon" /></a></p>
 ````````````````````````````````
 
 
 However, links may not contain other links, at any level of nesting.
 
 ```````````````````````````````` example
 [foo [bar](/uri)][ref]
 
 [ref]: /uri
 .
 <p>[foo <a href="/uri">bar</a>]<a href="/uri">ref</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo *bar [baz][ref]*][ref]
 
 [ref]: /uri
 .
 <p>[foo <em>bar <a href="/uri">baz</a></em>]<a href="/uri">ref</a></p>
 ````````````````````````````````
 
 
 (In the examples above, we have two [shortcut reference links]
 instead of one [full reference link].)
 
 The following cases illustrate the precedence of link text grouping over
 emphasis grouping:
 
 ```````````````````````````````` example
 *[foo*][ref]
 
 [ref]: /uri
 .
 <p>*<a href="/uri">foo*</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo *bar][ref]
 
 [ref]: /uri
 .
 <p><a href="/uri">foo *bar</a></p>
 ````````````````````````````````
 
 
 These cases illustrate the precedence of HTML tags, code spans,
 and autolinks over link grouping:
 
 ```````````````````````````````` example
 [foo <bar attr="][ref]">
 
 [ref]: /uri
 .
 <p>[foo <bar attr="][ref]"></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo`][ref]`
 
 [ref]: /uri
 .
 <p>[foo<code>][ref]</code></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo<http://example.com/?search=][ref]>
 
 [ref]: /uri
 .
 <p>[foo<a href="http://example.com/?search=%5D%5Bref%5D">http://example.com/?search=][ref]</a></p>
 ````````````````````````````````
 
 
 Matching is case-insensitive:
 
 ```````````````````````````````` example
 [foo][BaR]
 
 [bar]: /url "title"
 .
 <p><a href="/url" title="title">foo</a></p>
 ````````````````````````````````
 
 
 Unicode case fold is used:
 
 ```````````````````````````````` example
 [Толпой][Толпой] is a Russian word.
 
 [ТОЛПОЙ]: /url
 .
 <p><a href="/url">Толпой</a> is a Russian word.</p>
 ````````````````````````````````
 
 
 Consecutive internal [whitespace] is treated as one space for
 purposes of determining matching:
 
 ```````````````````````````````` example
 [Foo
   bar]: /url
 
 [Baz][Foo bar]
 .
 <p><a href="/url">Baz</a></p>
 ````````````````````````````````
 
 
 No [whitespace] is allowed between the [link text] and the
 [link label]:
 
 ```````````````````````````````` example
 [foo] [bar]
 
 [bar]: /url "title"
 .
 <p>[foo] <a href="/url" title="title">bar</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo]
 [bar]
 
 [bar]: /url "title"
 .
 <p>[foo]
 <a href="/url" title="title">bar</a></p>
 ````````````````````````````````
 
 
 This is a departure from John Gruber's original Markdown syntax
 description, which explicitly allows whitespace between the link
 text and the link label.  It brings reference links in line with
 [inline links], which (according to both original Markdown and
 this spec) cannot have whitespace after the link text.  More
 importantly, it prevents inadvertent capture of consecutive
 [shortcut reference links]. If whitespace is allowed between the
 link text and the link label, then in the following we will have
 a single reference link, not two shortcut reference links, as
 intended:
 
 ``` 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]
 .
 <p><a href="/url1">bar</a></p>
 ````````````````````````````````
 
 
 Note that matching is performed on normalized strings, not parsed
 inline content.  So the following does not match, even though the
 labels define equivalent inline content:
 
 ```````````````````````````````` example
 [bar][foo\!]
 
 [foo!]: /url
 .
 <p>[bar][foo!]</p>
 ````````````````````````````````
 
 
 [Link labels] cannot contain brackets, unless they are
 backslash-escaped:
 
 ```````````````````````````````` example
 [foo][ref[]
 
 [ref[]: /uri
 .
 <p>[foo][ref[]</p>
 <p>[ref[]: /uri</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo][ref[bar]]
 
 [ref[bar]]: /uri
 .
 <p>[foo][ref[bar]]</p>
 <p>[ref[bar]]: /uri</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [[[foo]]]
 
 [[[foo]]]: /url
 .
 <p>[[[foo]]]</p>
 <p>[[[foo]]]: /url</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [foo][ref\[]
 
 [ref\[]: /uri
 .
 <p><a href="/uri">foo</a></p>
 ````````````````````````````````
 
 
 Note that in this example `]` is not backslash-escaped:
 
 ```````````````````````````````` example
 [bar\\]: /uri
 
 [bar\\]
 .
 <p><a href="/uri">bar\</a></p>
 ````````````````````````````````
 
 
 A [link label] must contain at least one [non-whitespace character]:
 
 ```````````````````````````````` example
 []
 
 []: /uri
 .
 <p>[]</p>
 <p>[]: /uri</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [
  ]
 
 [
  ]: /uri
 .
 <p>[
 ]</p>
 <p>[
 ]: /uri</p>
 ````````````````````````````````
 
 
 A [collapsed reference link](@)
 consists of a [link label] that [matches] a
 [link reference definition] elsewhere in the
 document, followed by the string `[]`.
 The contents of the 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"
 .
 <p><a href="/url" title="title">foo</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [*foo* bar][]
 
 [*foo* bar]: /url "title"
 .
 <p><a href="/url" title="title"><em>foo</em> bar</a></p>
 ````````````````````````````````
 
 
 The link labels are case-insensitive:
 
 ```````````````````````````````` example
 [Foo][]
 
 [foo]: /url "title"
 .
 <p><a href="/url" title="title">Foo</a></p>
 ````````````````````````````````
 
 
 
 As with full reference links, [whitespace] is not
 allowed between the two sets of brackets:
 
 ```````````````````````````````` example
 [foo] 
 []
 
 [foo]: /url "title"
 .
 <p><a href="/url" title="title">foo</a>
 []</p>
 ````````````````````````````````
 
 
 A [shortcut reference link](@)
 consists of a [link label] that [matches] a
 [link reference definition] elsewhere in the
 document and is not followed by `[]` or a link label.
 The contents of the first link label are parsed as inlines,
 which are used as the link's text.  The link's URI and title
 are provided by the matching link reference definition.
 Thus, `[foo]` is equivalent to `[foo][]`.
 
 ```````````````````````````````` example
 [foo]
 
 [foo]: /url "title"
 .
 <p><a href="/url" title="title">foo</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [*foo* bar]
 
 [*foo* bar]: /url "title"
 .
 <p><a href="/url" title="title"><em>foo</em> bar</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [[*foo* bar]]
 
 [*foo* bar]: /url "title"
 .
 <p>[<a href="/url" title="title"><em>foo</em> bar</a>]</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 [[bar [foo]
 
 [foo]: /url
 .
 <p>[[bar <a href="/url">foo</a></p>
 ````````````````````````````````
 
 
 The link labels are case-insensitive:
 
 ```````````````````````````````` example
 [Foo]
 
 [foo]: /url "title"
 .
 <p><a href="/url" title="title">Foo</a></p>
 ````````````````````````````````
 
 
 A space after the link text should be preserved:
 
 ```````````````````````````````` example
 [foo] bar
 
 [foo]: /url
 .
 <p><a href="/url">foo</a> bar</p>
 ````````````````````````````````
 
 
 If you just want bracketed text, you can backslash-escape the
 opening bracket to avoid links:
 
 ```````````````````````````````` example
 \[foo]
 
 [foo]: /url "title"
 .
 <p>[foo]</p>
 ````````````````````````````````
 
 
 Note that this is a link, because a link label ends with the first
 following closing bracket:
 
 ```````````````````````````````` example
 [foo*]: /url
 
 *[foo*]
 .
 <p>*<a href="/url">foo*</a></p>
 ````````````````````````````````
 
 
 Full and compact references take precedence over shortcut
 references:
 
 ```````````````````````````````` example
 [foo][bar]
 
 [foo]: /url1
 [bar]: /url2
 .
 <p><a href="/url2">foo</a></p>
 ````````````````````````````````
 
 ```````````````````````````````` example
 [foo][]
 
 [foo]: /url1
 .
 <p><a href="/url1">foo</a></p>
 ````````````````````````````````
 
 Inline links also take precedence:
 
 ```````````````````````````````` example
 [foo]()
 
 [foo]: /url1
 .
 <p><a href="">foo</a></p>
 ````````````````````````````````
 
 ```````````````````````````````` example
 [foo](not a link)
 
 [foo]: /url1
 .
 <p><a href="/url1">foo</a>(not a link)</p>
 ````````````````````````````````
 
 In the following case `[bar][baz]` is parsed as a reference,
 `[foo]` as normal text:
 
 ```````````````````````````````` example
 [foo][bar][baz]
 
 [baz]: /url
 .
 <p>[foo]<a href="/url">bar</a></p>
 ````````````````````````````````
 
 
 Here, though, `[foo][bar]` is parsed as a reference, since
 `[bar]` is defined:
 
 ```````````````````````````````` example
 [foo][bar][baz]
 
 [baz]: /url1
 [bar]: /url2
 .
 <p><a href="/url2">foo</a><a href="/url1">baz</a></p>
 ````````````````````````````````
 
 
 Here `[foo]` is not parsed as a shortcut reference, because it
 is followed by a link label (even though `[bar]` is not defined):
 
 ```````````````````````````````` example
 [foo][bar][baz]
 
 [baz]: /url1
 [foo]: /url2
 .
 <p>[foo]<a href="/url1">bar</a></p>
 ````````````````````````````````
 
 
 
 ## 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")
 .
 <p><img src="/url" alt="foo" title="title" /></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ![foo *bar*]
 
 [foo *bar*]: train.jpg "train & tracks"
 .
 <p><img src="train.jpg" alt="foo bar" title="train &amp; tracks" /></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ![foo ![bar](/url)](/url2)
 .
 <p><img src="/url2" alt="foo bar" /></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ![foo [bar](/url)](/url2)
 .
 <p><img src="/url2" alt="foo bar" /></p>
 ````````````````````````````````
 
 
 Though this spec is concerned with parsing, not rendering, it is
 recommended that in rendering to HTML, only the plain string content
 of the [image description] be used.  Note that in
 the above example, the alt attribute's value is `foo bar`, not `foo
 [bar](/url)` or `foo <a href="/url">bar</a>`.  Only the plain string
 content is rendered, without formatting.
 
 ```````````````````````````````` example
 ![foo *bar*][]
 
 [foo *bar*]: train.jpg "train & tracks"
 .
 <p><img src="train.jpg" alt="foo bar" title="train &amp; tracks" /></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ![foo *bar*][foobar]
 
 [FOOBAR]: train.jpg "train & tracks"
 .
 <p><img src="train.jpg" alt="foo bar" title="train &amp; tracks" /></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ![foo](train.jpg)
 .
 <p><img src="train.jpg" alt="foo" /></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 My ![foo bar](/path/to/train.jpg  "title"   )
 .
 <p>My <img src="/path/to/train.jpg" alt="foo bar" title="title" /></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ![foo](<url>)
 .
 <p><img src="url" alt="foo" /></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ![](/url)
 .
 <p><img src="/url" alt="" /></p>
 ````````````````````````````````
 
 
 Reference-style:
 
 ```````````````````````````````` example
 ![foo][bar]
 
 [bar]: /url
 .
 <p><img src="/url" alt="foo" /></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ![foo][bar]
 
 [BAR]: /url
 .
 <p><img src="/url" alt="foo" /></p>
 ````````````````````````````````
 
 
 Collapsed:
 
 ```````````````````````````````` example
 ![foo][]
 
 [foo]: /url "title"
 .
 <p><img src="/url" alt="foo" title="title" /></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ![*foo* bar][]
 
 [*foo* bar]: /url "title"
 .
 <p><img src="/url" alt="foo bar" title="title" /></p>
 ````````````````````````````````
 
 
 The labels are case-insensitive:
 
 ```````````````````````````````` example
 ![Foo][]
 
 [foo]: /url "title"
 .
 <p><img src="/url" alt="Foo" title="title" /></p>
 ````````````````````````````````
 
 
 As with reference links, [whitespace] is not allowed
 between the two sets of brackets:
 
 ```````````````````````````````` example
 ![foo] 
 []
 
 [foo]: /url "title"
 .
 <p><img src="/url" alt="foo" title="title" />
 []</p>
 ````````````````````````````````
 
 
 Shortcut:
 
 ```````````````````````````````` example
 ![foo]
 
 [foo]: /url "title"
 .
 <p><img src="/url" alt="foo" title="title" /></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ![*foo* bar]
 
 [*foo* bar]: /url "title"
 .
 <p><img src="/url" alt="foo bar" title="title" /></p>
 ````````````````````````````````
 
 
 Note that link labels cannot contain unescaped brackets:
 
 ```````````````````````````````` example
 ![[foo]]
 
 [[foo]]: /url "title"
 .
 <p>![[foo]]</p>
 <p>[[foo]]: /url &quot;title&quot;</p>
 ````````````````````````````````
 
 
 The link labels are case-insensitive:
 
 ```````````````````````````````` example
 ![Foo]
 
 [foo]: /url "title"
 .
 <p><img src="/url" alt="Foo" title="title" /></p>
 ````````````````````````````````
 
 
 If you just want a literal `!` followed by bracketed text, you can
 backslash-escape the opening `[`:
 
 ```````````````````````````````` example
 !\[foo]
 
 [foo]: /url "title"
 .
 <p>![foo]</p>
 ````````````````````````````````
 
 
 If you want a link after a literal `!`, backslash-escape the
 `!`:
 
 ```````````````````````````````` example
 \![foo]
 
 [foo]: /url "title"
 .
 <p>!<a href="/url" title="title">foo</a></p>
 ````````````````````````````````
 
 
 ## 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] not containing `<`, followed by `>`.  It is parsed as
 a link to the URI, with the URI as the link's label.
 
 An [absolute URI](@),
 for these purposes, consists of a [scheme] followed by a colon (`:`)
 followed by zero or more characters other than ASCII
 [whitespace] and control characters, `<`, and `>`.  If
 the URI includes these characters, 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>
 .
 <p><a href="http://foo.bar.baz">http://foo.bar.baz</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <http://foo.bar.baz/test?q=hello&id=22&boolean>
 .
 <p><a href="http://foo.bar.baz/test?q=hello&amp;id=22&amp;boolean">http://foo.bar.baz/test?q=hello&amp;id=22&amp;boolean</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <irc://foo.bar:2233/baz>
 .
 <p><a href="irc://foo.bar:2233/baz">irc://foo.bar:2233/baz</a></p>
 ````````````````````````````````
 
 
 Uppercase is also fine:
 
 ```````````````````````````````` example
 <MAILTO:FOO@BAR.BAZ>
 .
 <p><a href="MAILTO:FOO@BAR.BAZ">MAILTO:FOO@BAR.BAZ</a></p>
 ````````````````````````````````
 
 
 Note that many strings that count as [absolute URIs] for
 purposes of this spec are not valid URIs, because their
 schemes are not registered or because of other problems
 with their syntax:
 
 ```````````````````````````````` example
 <a+b+c:d>
 .
 <p><a href="a+b+c:d">a+b+c:d</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <made-up-scheme://foo,bar>
 .
 <p><a href="made-up-scheme://foo,bar">made-up-scheme://foo,bar</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <http://../>
 .
 <p><a href="http://../">http://../</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <localhost:5001/foo>
 .
 <p><a href="localhost:5001/foo">localhost:5001/foo</a></p>
 ````````````````````````````````
 
 
 Spaces are not allowed in autolinks:
 
 ```````````````````````````````` example
 <http://foo.bar/baz bim>
 .
 <p>&lt;http://foo.bar/baz bim&gt;</p>
 ````````````````````````````````
 
 
 Backslash-escapes do not work inside autolinks:
 
 ```````````````````````````````` example
 <http://example.com/\[\>
 .
 <p><a href="http://example.com/%5C%5B%5C">http://example.com/\[\</a></p>
 ````````````````````````````````
 
 
 An [email autolink](@)
 consists of `<`, followed by an [email address],
 followed by `>`.  The link's label is the email address,
 and the URL is `mailto:` followed by the email address.
 
 An [email address](@),
 for these purposes, is anything that matches
 the [non-normative regex from the HTML5
 spec](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>
 .
 <p><a href="mailto:foo@bar.example.com">foo@bar.example.com</a></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <foo+special@Bar.baz-bar0.com>
 .
 <p><a href="mailto:foo+special@Bar.baz-bar0.com">foo+special@Bar.baz-bar0.com</a></p>
 ````````````````````````````````
 
 
 Backslash-escapes do not work inside email autolinks:
 
 ```````````````````````````````` example
 <foo\+@bar.example.com>
 .
 <p>&lt;foo+@bar.example.com&gt;</p>
 ````````````````````````````````
 
 
 These are not autolinks:
 
 ```````````````````````````````` example
 <>
 .
 <p>&lt;&gt;</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 < http://foo.bar >
 .
 <p>&lt; http://foo.bar &gt;</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <m:abc>
 .
 <p>&lt;m:abc&gt;</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <foo.bar.baz>
 .
 <p>&lt;foo.bar.baz&gt;</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 http://example.com
 .
 <p>http://example.com</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo@bar.example.com
 .
 <p>foo@bar.example.com</p>
 ````````````````````````````````
 
 
 ## 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 [whitespace],
 an [attribute name], and an optional
 [attribute value specification].
 
 An [attribute name](@)
 consists of an ASCII letter, `_`, or `:`, followed by zero or more ASCII
 letters, digits, `_`, `.`, `:`, or `-`.  (Note:  This is the XML
 specification restricted to ASCII.  HTML5 is laxer.)
 
 An [attribute value specification](@)
 consists of optional [whitespace],
 a `=` character, optional [whitespace], and an [attribute
 value].
 
 An [attribute value](@)
 consists of an [unquoted attribute value],
 a [single-quoted attribute value], or a [double-quoted attribute value].
 
 An [unquoted attribute value](@)
 is a nonempty string of characters not
 including spaces, `"`, `'`, `=`, `<`, `>`, or `` ` ``.
 
 A [single-quoted attribute value](@)
 consists of `'`, zero or more
 characters not including `'`, and a final `'`.
 
 A [double-quoted attribute value](@)
 consists of `"`, zero or more
 characters not including `"`, and a final `"`.
 
 An [open tag](@) consists of a `<` character, a [tag name],
 zero or more [attributes], optional [whitespace], an optional `/`
 character, and a `>` character.
 
 A [closing tag](@) consists of the string `</`, a
 [tag name], optional [whitespace], and the character `>`.
 
 An [HTML comment](@) consists of `<!--` + *text* + `-->`,
 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 `<?`, a string
 of characters not including the string `?>`, and the string
 `?>`.
 
 A [declaration](@) consists of the
 string `<!`, a name consisting of one or more uppercase ASCII letters,
 [whitespace], a string of characters not including the
 character `>`, and the character `>`.
 
 A [CDATA section](@) consists of
 the string `<![CDATA[`, a string of characters not including the string
 `]]>`, and the string `]]>`.
 
 An [HTML tag](@) consists of an [open tag], a [closing tag],
 an [HTML comment], a [processing instruction], a [declaration],
 or a [CDATA section].
 
 Here are some simple open tags:
 
 ```````````````````````````````` example
 <a><bab><c2c>
 .
 <p><a><bab><c2c></p>
 ````````````````````````````````
 
 
 Empty elements:
 
 ```````````````````````````````` example
 <a/><b2/>
 .
 <p><a/><b2/></p>
 ````````````````````````````````
 
 
 [Whitespace] is allowed:
 
 ```````````````````````````````` example
 <a  /><b2
 data="foo" >
 .
 <p><a  /><b2
 data="foo" ></p>
 ````````````````````````````````
 
 
 With attributes:
 
 ```````````````````````````````` example
 <a foo="bar" bam = 'baz <em>"</em>'
 _boolean zoop:33=zoop:33 />
 .
 <p><a foo="bar" bam = 'baz <em>"</em>'
 _boolean zoop:33=zoop:33 /></p>
 ````````````````````````````````
 
 
 Custom tag names can be used:
 
 ```````````````````````````````` example
 Foo <responsive-image src="foo.jpg" />
 .
 <p>Foo <responsive-image src="foo.jpg" /></p>
 ````````````````````````````````
 
 
 Illegal tag names, not parsed as HTML:
 
 ```````````````````````````````` example
 <33> <__>
 .
 <p>&lt;33&gt; &lt;__&gt;</p>
 ````````````````````````````````
 
 
 Illegal attribute names:
 
 ```````````````````````````````` example
 <a h*#ref="hi">
 .
 <p>&lt;a h*#ref=&quot;hi&quot;&gt;</p>
 ````````````````````````````````
 
 
 Illegal attribute values:
 
 ```````````````````````````````` example
 <a href="hi'> <a href=hi'>
 .
 <p>&lt;a href=&quot;hi'&gt; &lt;a href=hi'&gt;</p>
 ````````````````````````````````
 
 
 Illegal [whitespace]:
 
 ```````````````````````````````` example
 < a><
 foo><bar/ >
 .
 <p>&lt; a&gt;&lt;
 foo&gt;&lt;bar/ &gt;</p>
 ````````````````````````````````
 
 
 Missing [whitespace]:
 
 ```````````````````````````````` example
 <a href='bar'title=title>
 .
 <p>&lt;a href='bar'title=title&gt;</p>
 ````````````````````````````````
 
 
 Closing tags:
 
 ```````````````````````````````` example
 </a></foo >
 .
 <p></a></foo ></p>
 ````````````````````````````````
 
 
 Illegal attributes in closing tag:
 
 ```````````````````````````````` example
 </a href="foo">
 .
 <p>&lt;/a href=&quot;foo&quot;&gt;</p>
 ````````````````````````````````
 
 
 Comments:
 
 ```````````````````````````````` example
 foo <!-- this is a
 comment - with hyphen -->
 .
 <p>foo <!-- this is a
 comment - with hyphen --></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo <!-- not a comment -- two hyphens -->
 .
 <p>foo &lt;!-- not a comment -- two hyphens --&gt;</p>
 ````````````````````````````````
 
 
 Not comments:
 
 ```````````````````````````````` example
 foo <!--> foo -->
 
 foo <!-- foo--->
 .
 <p>foo &lt;!--&gt; foo --&gt;</p>
 <p>foo &lt;!-- foo---&gt;</p>
 ````````````````````````````````
 
 
 Processing instructions:
 
 ```````````````````````````````` example
 foo <?php echo $a; ?>
 .
 <p>foo <?php echo $a; ?></p>
 ````````````````````````````````
 
 
 Declarations:
 
 ```````````````````````````````` example
 foo <!ELEMENT br EMPTY>
 .
 <p>foo <!ELEMENT br EMPTY></p>
 ````````````````````````````````
 
 
 CDATA sections:
 
 ```````````````````````````````` example
 foo <![CDATA[>&<]]>
 .
 <p>foo <![CDATA[>&<]]></p>
 ````````````````````````````````
 
 
 Entity and numeric character references are preserved in HTML
 attributes:
 
 ```````````````````````````````` example
 foo <a href="&ouml;">
 .
 <p>foo <a href="&ouml;"></p>
 ````````````````````````````````
 
 
 Backslash escapes do not work in HTML attributes:
 
 ```````````````````````````````` example
 foo <a href="\*">
 .
 <p>foo <a href="\*"></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <a href="\"">
 .
 <p>&lt;a href=&quot;&quot;&quot;&gt;</p>
 ````````````````````````````````
 
 
 ## Hard line breaks
 
 A line break (not in a code span or HTML tag) that is preceded
 by two or more spaces and does not occur at the end of a block
 is parsed as a [hard line break](@) (rendered
 in HTML as a `<br />` tag):
 
 ```````````````````````````````` example
 foo  
 baz
 .
 <p>foo<br />
 baz</p>
 ````````````````````````````````
 
 
 For a more visible alternative, a backslash before the
 [line ending] may be used instead of two spaces:
 
 ```````````````````````````````` example
 foo\
 baz
 .
 <p>foo<br />
 baz</p>
 ````````````````````````````````
 
 
 More than two spaces can be used:
 
 ```````````````````````````````` example
 foo       
 baz
 .
 <p>foo<br />
 baz</p>
 ````````````````````````````````
 
 
 Leading spaces at the beginning of the next line are ignored:
 
 ```````````````````````````````` example
 foo  
      bar
 .
 <p>foo<br />
 bar</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo\
      bar
 .
 <p>foo<br />
 bar</p>
 ````````````````````````````````
 
 
 Line breaks can occur inside emphasis, links, and other constructs
 that allow inline content:
 
 ```````````````````````````````` example
 *foo  
 bar*
 .
 <p><em>foo<br />
 bar</em></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 *foo\
 bar*
 .
 <p><em>foo<br />
 bar</em></p>
 ````````````````````````````````
 
 
 Line breaks do not occur inside code spans
 
 ```````````````````````````````` example
 `code  
 span`
 .
 <p><code>code span</code></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 `code\
 span`
 .
 <p><code>code\ span</code></p>
 ````````````````````````````````
 
 
 or HTML tags:
 
 ```````````````````````````````` example
 <a href="foo  
 bar">
 .
 <p><a href="foo  
 bar"></p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 <a href="foo\
 bar">
 .
 <p><a href="foo\
 bar"></p>
 ````````````````````````````````
 
 
 Hard line breaks are for separating inline content within a block.
 Neither syntax for hard line breaks works at the end of a paragraph or
 other block element:
 
 ```````````````````````````````` example
 foo\
 .
 <p>foo\</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 foo  
 .
 <p>foo</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ### foo\
 .
 <h3>foo\</h3>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 ### foo  
 .
 <h3>foo</h3>
 ````````````````````````````````
 
 
 ## Soft line breaks
 
 A regular line break (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 softbreak may be rendered in HTML either as a
 [line ending] or as a space. The result will be the same in
 browsers. In the examples here, a [line ending] will be used.)
 
 ```````````````````````````````` example
 foo
 baz
 .
 <p>foo
 baz</p>
 ````````````````````````````````
 
 
 Spaces at the end of the line and beginning of the next line are
 removed:
 
 ```````````````````````````````` example
 foo 
  baz
 .
 <p>foo
 baz</p>
 ````````````````````````````````
 
 
 A conforming parser may render a soft line break in HTML either as a
 line break or as a space.
 
 A renderer may also provide an option to render soft line breaks
 as hard line breaks.
 
 ## Textual content
 
 Any characters not given an interpretation by the above rules will
 be parsed as plain textual content.
 
 ```````````````````````````````` example
 hello $.;'there
 .
 <p>hello $.;'there</p>
 ````````````````````````````````
 
 
 ```````````````````````````````` example
 Foo χρῆν
 .
 <p>Foo χρῆν</p>
 ````````````````````````````````
 
 
 Internal spaces are preserved verbatim:
 
 ```````````````````````````````` example
 Multiple     spaces
 .
 <p>Multiple     spaces</p>
 ````````````````````````````````
 
 
 <!-- END TESTS -->
 
 # 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 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 (`*`, `_`).  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 in 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.