diff options
Diffstat (limited to 'core/testdata/markdown/spec.txt')
| -rw-r--r-- | core/testdata/markdown/spec.txt | 6150 |
1 files changed, 0 insertions, 6150 deletions
diff --git a/core/testdata/markdown/spec.txt b/core/testdata/markdown/spec.txt deleted file mode 100644 index 916bdd89..00000000 --- a/core/testdata/markdown/spec.txt +++ /dev/null @@ -1,6150 +0,0 @@ ---- -title: CommonMark Spec -author: -- John MacFarlane -version: 2 -date: 2014-09-19 -... - -# Introduction - -## What is Markdown? - -Markdown is a plain text format for writing structured documents, -based on conventions used for indicating formatting in email and -usenet posts. It was developed in 2004 by John Gruber, who wrote -the first Markdown-to-HTML converter in perl, and it soon became -widely used in websites. By 2014 there were dozens of -implementations in many languages. Some of them extended basic -Markdown syntax with conventions for footnotes, definition lists, -tables, and other constructs, and some allowed output not just in -HTML but in LaTeX and many other formats. - -## Why is a spec needed? - -John Gruber's [canonical description of Markdown's -syntax](https://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](https://article.gmane.org/gmane.text.markdown.general/1997).) - -2. Is a blank line needed before a block quote or header? - Most implementations do not require the blank line. However, - this can lead to unexpected results in hard-wrapped text, and - also to ambiguities in parsing (note that some implementations - put the header inside the blockquote, while others do not). - (John Gruber has also spoken [in favor of requiring the blank - lines](https://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](https://article.gmane.org/gmane.text.markdown.general/2554).) - -5. Can list markers be indented? Can ordered list markers be right-aligned? - - ``` markdown - 8. item 1 - 9. item 2 - 10. item 2a - ``` - -6. Is this one list with a horizontal rule in its second item, - or two lists separated by a horizontal rule? - - ``` markdown - * a - * * * * * - * b - ``` - -7. When list markers change from numbers to bullets, do we have - two lists or one? (The Markdown syntax description suggests two, - but the perl scripts and many other implementations produce one.) - - ``` markdown - 1. fee - 2. fie - - foe - - fum - ``` - -8. What are the precedence rules for the markers of inline structure? - For example, is the following a valid link, or does the code span - take precedence ? - - ``` markdown - [a backtick (`)](/url) and [another backtick (`)](/url). - ``` - -9. What are the precedence rules for markers of emphasis and strong - emphasis? For example, how should the following be parsed? - - ``` markdown - *foo *bar* baz* - ``` - -10. What are the precedence rules between block-level and inline-level - structure? For example, how should the following be parsed? - - ``` markdown - - `a long code span can contain a hyphen like this - - and it can screw things up` - ``` - -11. Can list items include headers? (`Markdown.pl` does not allow this, - but headers can occur in blockquotes.) - - ``` markdown - - # Heading - ``` - -12. Can link references be defined inside block quotes or list items? - - ``` markdown - > Blockquote [foo]. - > - > [foo]: /url - ``` - -13. 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 `runtests.pl` can be used to run the tests -against any Markdown program: - - perl runtests.pl spec.txt PROGRAM - -Since this document describes how Markdown is to be parsed into -an abstract syntax tree, it would have made sense to use an abstract -representation of the syntax tree instead of HTML. But HTML is capable -of representing the structural distinctions we need to make, and the -choice of HTML for the tests makes it possible to run the tests against -an implementation without writing an abstract syntax tree renderer. - -This document is generated from a text file, `spec.txt`, written -in Markdown with a small extension for the side-by-side tests. -The script `spec2md.pl` can be used to turn `spec.txt` into pandoc -Markdown, which can then be converted into other formats. - -In the examples, the `→` character is used to represent tabs. - -# Preprocessing - -A [line](#line) <a id="line"></a> -is a sequence of zero or more characters followed by a line -ending (CR, LF, or CRLF) or by the end of -file. - -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. - -Tabs in lines are expanded to spaces, with a tab stop of 4 characters: - -. -→foo→baz→→bim -. -<pre><code>foo baz bim -</code></pre> -. - -. - a→a - ὐ→a -. -<pre><code>a a -ὐ a -</code></pre> -. - -Line endings are replaced by newline characters (LF). - -A line containing no characters, or a line containing only spaces (after -tab expansion), is called a [blank line](#blank-line). -<a id="blank-line"></a> - -# Blocks and inlines - -We can think of a document as a sequence of [blocks](#block)<a -id="block"></a>---structural elements like paragraphs, block quotations, -lists, headers, rules, and code blocks. Blocks can contain other -blocks, or they can contain [inline](#inline)<a id="inline"></a> content: -words, spaces, links, emphasized text, images, and inline code. - -## Precedence - -Indicators of block structure always take precedence over indicators -of inline structure. So, for example, the following is a list with -two items, not a list with one item containing a code span: - -. -- `one -- two` -. -<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, headers, and other block constructs can be parsed for inline -structure. The second step requires information about link reference -definitions that will be available only at the end of the first -step. Note that the first step requires processing lines in sequence, -but the second can be parallelized, since the inline parsing of -one block element does not affect the inline parsing of any other. - -## Container blocks and leaf blocks - -We can divide blocks into two types: -[container blocks](#container-block), <a id="container-block"></a> -which can contain other blocks, and [leaf blocks](#leaf-block), -<a id="leaf-block"></a> which cannot. - -# Leaf blocks - -This section describes the different kinds of leaf block that make up a -Markdown document. - -## Horizontal rules - -A line consisting of 0-3 spaces of indentation, followed by a sequence -of three or more matching `-`, `_`, or `*` characters, each followed -optionally by any number of spaces, forms a [horizontal -rule](#horizontal-rule). <a id="horizontal-rule"></a> - -. -*** ---- -___ -. -<hr /> -<hr /> -<hr /> -. - -Wrong characters: - -. -+++ -. -<p>+++</p> -. - -. -=== -. -<p>===</p> -. - -Not enough characters: - -. --- -** -__ -. -<p>-- -** -__</p> -. - -One to three spaces indent are allowed: - -. - *** - *** - *** -. -<hr /> -<hr /> -<hr /> -. - -Four spaces is too many: - -. - *** -. -<pre><code>*** -</code></pre> -. - -. -Foo - *** -. -<p>Foo -***</p> -. - -More than three characters may be used: - -. -_____________________________________ -. -<hr /> -. - -Spaces are allowed between the characters: - -. - - - - -. -<hr /> -. - -. - ** * ** * ** * ** -. -<hr /> -. - -. -- - - - -. -<hr /> -. - -Spaces are allowed at the end: - -. -- - - - -. -<hr /> -. - -However, no other characters may occur at the end or the -beginning: - -. -_ _ _ _ a - -a------ -. -<p>_ _ _ _ a</p> -<p>a------</p> -. - -It is required that all of the non-space characters be the same. -So, this is not a horizontal rule: - -. - *-* -. -<p><em>-</em></p> -. - -Horizontal rules do not need blank lines before or after: - -. -- foo -*** -- bar -. -<ul> -<li>foo</li> -</ul> -<hr /> -<ul> -<li>bar</li> -</ul> -. - -Horizontal rules can interrupt a paragraph: - -. -Foo -*** -bar -. -<p>Foo</p> -<hr /> -<p>bar</p> -. - -Note, however, that this is a setext header, not a paragraph followed -by a horizontal rule: - -. -Foo ---- -bar -. -<h2>Foo</h2> -<p>bar</p> -. - -When both a horizontal rule and a list item are possible -interpretations of a line, the horizontal rule is preferred: - -. -* Foo -* * * -* Bar -. -<ul> -<li>Foo</li> -</ul> -<hr /> -<ul> -<li>Bar</li> -</ul> -. - -If you want a horizontal rule in a list item, use a different bullet: - -. -- Foo -- * * * -. -<ul> -<li>Foo</li> -<li><hr /></li> -</ul> -. - -## ATX headers - -An [ATX header](#atx-header) <a id="atx-header"></a> -consists of a string of characters, parsed as inline content, between an -opening sequence of 1--6 unescaped `#` characters and an optional -closing sequence of any number of `#` characters. The opening sequence -of `#` characters cannot be followed directly by a nonspace character. -The closing `#` characters may be followed by spaces only. The opening -`#` character may be indented 0-3 spaces. The raw contents of the -header are stripped of leading and trailing spaces before being parsed -as inline content. The header level is equal to the number of `#` -characters in the opening sequence. - -Simple headers: - -. -# foo -## foo -### foo -#### foo -##### foo -###### foo -. -<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 header: - -. -####### foo -. -<p>####### foo</p> -. - -A space is required between the `#` characters and the header's -contents. Note that many implementations currently do not require -the space. However, the space was required by the [original ATX -implementation](https://www.aaronsw.com/2002/atx/atx.py), and it helps -prevent things like the following from being parsed as headers: - -. -#5 bolt -. -<p>#5 bolt</p> -. - -This is not a header, because the first `#` is escaped: - -. -\## foo -. -<p>## foo</p> -. - -Contents are parsed as inlines: - -. -# foo *bar* \*baz\* -. -<h1>foo <em>bar</em> *baz*</h1> -. - -Leading and trailing blanks are ignored in parsing inline content: - -. -# foo -. -<h1>foo</h1> -. - -One to three spaces indentation are allowed: - -. - ### foo - ## foo - # foo -. -<h3>foo</h3> -<h2>foo</h2> -<h1>foo</h1> -. - -Four spaces are too much: - -. - # foo -. -<pre><code># foo -</code></pre> -. - -. -foo - # bar -. -<p>foo -# bar</p> -. - -A closing sequence of `#` characters is optional: - -. -## foo ## - ### bar ### -. -<h2>foo</h2> -<h3>bar</h3> -. - -It need not be the same length as the opening sequence: - -. -# foo ################################## -##### foo ## -. -<h1>foo</h1> -<h5>foo</h5> -. - -Spaces are allowed after the closing sequence: - -. -### foo ### -. -<h3>foo</h3> -. - -A sequence of `#` characters with a nonspace character following it -is not a closing sequence, but counts as part of the contents of the -header: - -. -### foo ### b -. -<h3>foo ### b</h3> -. - -Backslash-escaped `#` characters do not count as part -of the closing sequence: - -. -### foo \### -## foo \#\## -# foo \# -. -<h3>foo #</h3> -<h2>foo ##</h2> -<h1>foo #</h1> -. - -ATX headers need not be separated from surrounding content by blank -lines, and they can interrupt paragraphs: - -. -**** -## foo -**** -. -<hr /> -<h2>foo</h2> -<hr /> -. - -. -Foo bar -# baz -Bar foo -. -<p>Foo bar</p> -<h1>baz</h1> -<p>Bar foo</p> -. - -ATX headers can be empty: - -. -## -# -### ### -. -<h2></h2> -<h1></h1> -<h3></h3> -. - -## Setext headers - -A [setext header](#setext-header) <a id="setext-header"></a> -consists of a line of text, containing at least one nonspace character, -with no more than 3 spaces indentation, followed by a [setext header -underline](#setext-header-underline). A [setext header -underline](#setext-header-underline) <a id="setext-header-underline"></a> -is a sequence of `=` characters or a sequence of `-` characters, with no -more than 3 spaces indentation and any number of trailing -spaces. The header is a level 1 header if `=` characters are used, and -a level 2 header if `-` characters are used. The contents of the header -are the result of parsing the first line as Markdown inline content. - -In general, a setext header need not be preceded or followed by a -blank line. However, it cannot interrupt a paragraph, so when a -setext header comes after a paragraph, a blank line is needed between -them. - -Simple examples: - -. -Foo *bar* -========= - -Foo *bar* ---------- -. -<h1>Foo <em>bar</em></h1> -<h2>Foo <em>bar</em></h2> -. - -The underlining can be any length: - -. -Foo -------------------------- - -Foo -= -. -<h2>Foo</h2> -<h1>Foo</h1> -. - -The header content can be indented up to three spaces, and need -not line up with the underlining: - -. - Foo ---- - - Foo ------ - - Foo - === -. -<h2>Foo</h2> -<h2>Foo</h2> -<h1>Foo</h1> -. - -Four spaces indent is too much: - -. - Foo - --- - - Foo ---- -. -<pre><code>Foo ---- - -Foo -</code></pre> -<hr /> -. - -The setext header underline can be indented up to three spaces, and -may have trailing spaces: - -. -Foo - ---- -. -<h2>Foo</h2> -. - -Four spaces is too much: - -. -Foo - --- -. -<p>Foo ----</p> -. - -The setext header underline cannot contain internal spaces: - -. -Foo -= = - -Foo ---- - -. -<p>Foo -= =</p> -<p>Foo</p> -<hr /> -. - -Trailing spaces in the content line do not cause a line break: - -. -Foo ------ -. -<h2>Foo</h2> -. - -Nor does a backslash at the end: - -. -Foo\ ----- -. -<h2>Foo\</h2> -. - -Since indicators of block structure take precedence over -indicators of inline structure, the following are setext headers: - -. -`Foo ----- -` - -<a title="a lot ---- -of dashes"/> -. -<h2>`Foo</h2> -<p>`</p> -<h2><a title="a lot</h2> -<p>of dashes"/></p> -. - -The setext header underline cannot be a lazy line: - -. -> Foo ---- -. -<blockquote> -<p>Foo</p> -</blockquote> -<hr /> -. - -A setext header cannot interrupt a paragraph: - -. -Foo -Bar ---- - -Foo -Bar -=== -. -<p>Foo -Bar</p> -<hr /> -<p>Foo -Bar -===</p> -. - -But in general a blank line is not required before or after: - -. ---- -Foo ---- -Bar ---- -Baz -. -<hr /> -<h2>Foo</h2> -<h2>Bar</h2> -<p>Baz</p> -. - -Setext headers cannot be empty: - -. - -==== -. -<p>====</p> -. - - -## Indented code blocks - -An [indented code block](#indented-code-block) -<a id="indented-code-block"></a> is composed of one or more -[indented chunks](#indented-chunk) separated by blank lines. -An [indented chunk](#indented-chunk) <a id="indented-chunk"></a> -is a sequence of non-blank lines, each indented four or more -spaces. An indented code block cannot interrupt a paragraph, so -if it occurs before or after a paragraph, there must be an -intervening blank line. The contents of the code block are -the literal contents of the lines, including trailing newlines, -minus four spaces of indentation. An indented code block has no -attributes. - -. - a simple - indented code block -. -<pre><code>a simple - indented code block -</code></pre> -. - -The contents are literal text, and do not get parsed as Markdown: - -. - <a/> - *hi* - - - one -. -<pre><code><a/> -*hi* - -- one -</code></pre> -. - -Here we have three chunks separated by blank lines: - -. - 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: - -. - chunk1 - - chunk2 -. -<pre><code>chunk1 - - chunk2 -</code></pre> -. - -An indented code block cannot interrupt a paragraph. (This -allows hanging indents and the like.) - -. -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: - -. - foo -bar -. -<pre><code>foo -</code></pre> -<p>bar</p> -. - -And indented code can occur immediately before and after other kinds of -blocks: - -. -# Header - foo -Header ------- - foo ----- -. -<h1>Header</h1> -<pre><code>foo -</code></pre> -<h2>Header</h2> -<pre><code>foo -</code></pre> -<hr /> -. - -The first line can be indented more than four spaces: - -. - foo - bar -. -<pre><code> foo -bar -</code></pre> -. - -Blank lines preceding or following an indented code block -are not included in it: - -. - - - foo - - -. -<pre><code>foo -</code></pre> -. - -Trailing spaces are included in the code block's content: - -. - foo -. -<pre><code>foo -</code></pre> -. - - -## Fenced code blocks - -A [code fence](#code-fence) <a id="code-fence"></a> is a sequence -of at least three consecutive backtick characters (`` ` ``) or -tildes (`~`). (Tildes and backticks cannot be mixed.) -A [fenced code block](#fenced-code-block) <a id="fenced-code-block"></a> -begins with a code fence, indented no more than three spaces. - -The line with the opening code fence may optionally contain some text -following the code fence; this is trimmed of leading and trailing -spaces and called the [info string](#info-string). -<a id="info-string"></a> 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](#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: - -. -``` -< - > -``` -. -<pre><code>< - > -</code></pre> -. - -With tildes: - -. -~~~ -< - > -~~~ -. -<pre><code>< - > -</code></pre> -. - -The closing code fence must use the same character as the opening -fence: - -. -``` -aaa -~~~ -``` -. -<pre><code>aaa -~~~ -</code></pre> -. - -. -~~~ -aaa -``` -~~~ -. -<pre><code>aaa -``` -</code></pre> -. - -The closing code fence must be at least as long as the opening fence: - -. -```` -aaa -``` -`````` -. -<pre><code>aaa -``` -</code></pre> -. - -. -~~~~ -aaa -~~~ -~~~~ -. -<pre><code>aaa -~~~ -</code></pre> -. - -Unclosed code blocks are closed by the end of the document: - -. -``` -. -<pre><code></code></pre> -. - -. -````` - -``` -aaa -. -<pre><code> -``` -aaa -</code></pre> -. - -A code block can have all empty lines as its content: - -. -``` - - -``` -. -<pre><code> - -</code></pre> -. - -A code block can be empty: - -. -``` -``` -. -<pre><code></code></pre> -. - -Fences can be indented. If the opening fence is indented, -content lines will have equivalent opening indentation removed, -if present: - -. - ``` - aaa -aaa -``` -. -<pre><code>aaa -aaa -</code></pre> -. - -. - ``` -aaa - aaa -aaa - ``` -. -<pre><code>aaa -aaa -aaa -</code></pre> -. - -. - ``` - aaa - aaa - aaa - ``` -. -<pre><code>aaa - aaa -aaa -</code></pre> -. - -Four spaces indentation produces an indented code block: - -. - ``` - aaa - ``` -. -<pre><code>``` -aaa -``` -</code></pre> -. - -Code fences (opening and closing) cannot contain internal spaces: - -. -``` ``` -aaa -. -<p><code></code> -aaa</p> -. - -. -~~~~~~ -aaa -~~~ ~~ -. -<pre><code>aaa -~~~ ~~ -</code></pre> -. - -Fenced code blocks can interrupt paragraphs, and can be followed -directly by paragraphs, without a blank line between: - -. -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: - -. -foo ---- -~~~ -bar -~~~ -# baz -. -<h2>foo</h2> -<pre><code>bar -</code></pre> -<h1>baz</h1> -. - -An [info string](#info-string) can be provided after the opening code fence. -Opening and closing spaces will be stripped, and the first word, prefixed -with `language-`, is used as the value for the `class` attribute of the -`code` element within the enclosing `pre` element. - -. -```ruby -def foo(x) - return 3 -end -``` -. -<pre><code class="language-ruby">def foo(x) - return 3 -end -</code></pre> -. - -. -~~~~ ruby startline=3 $%@#$ -def foo(x) - return 3 -end -~~~~~~~ -. -<pre><code class="language-ruby">def foo(x) - return 3 -end -</code></pre> -. - -. -````; -```` -. -<pre><code class="language-;"></code></pre> -. - -Info strings for backtick code blocks cannot contain backticks: - -. -``` aa ``` -foo -. -<p><code>aa</code> -foo</p> -. - -Closing code fences cannot have info strings: - -. -``` -``` aaa -``` -. -<pre><code>``` aaa -</code></pre> -. - - -## HTML blocks - -An [HTML block tag](#html-block-tag) <a id="html-block-tag"></a> is -an [open tag](#open-tag) or [closing tag](#closing-tag) whose tag -name is one of the following (case-insensitive): -`article`, `header`, `aside`, `hgroup`, `blockquote`, `hr`, `iframe`, -`body`, `li`, `map`, `button`, `object`, `canvas`, `ol`, `caption`, -`output`, `col`, `p`, `colgroup`, `pre`, `dd`, `progress`, `div`, -`section`, `dl`, `table`, `td`, `dt`, `tbody`, `embed`, `textarea`, -`fieldset`, `tfoot`, `figcaption`, `th`, `figure`, `thead`, `footer`, -`footer`, `tr`, `form`, `ul`, `h1`, `h2`, `h3`, `h4`, `h5`, `h6`, -`video`, `script`, `style`. - -An [HTML block](#html-block) <a id="html-block"></a> begins with an -[HTML block tag](#html-block-tag), [HTML comment](#html-comment), -[processing instruction](#processing-instruction), -[declaration](#declaration), or [CDATA section](#cdata-section). -It ends when a [blank line](#blank-line) or the end of the -input is encountered. The initial line may be indented up to three -spaces, and subsequent lines may have any indentation. The contents -of the HTML block are interpreted as raw HTML, and will not be escaped -in HTML output. - -Some simple examples: - -. -<table> - <tr> - <td> - hi - </td> - </tr> -</table> - -okay. -. -<table> - <tr> - <td> - hi - </td> - </tr> -</table> -<p>okay.</p> -. - -. - <div> - *hello* - <foo><a> -. - <div> - *hello* - <foo><a> -. - -Here we have two code blocks with a Markdown paragraph between them: - -. -<DIV CLASS="foo"> - -*Markdown* - -</DIV> -. -<DIV CLASS="foo"> -<p><em>Markdown</em></p> -</DIV> -. - -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: - -. -<div></div> -``` c -int x = 33; -``` -. -<div></div> -``` c -int x = 33; -``` -. - -A comment: - -. -<!-- Foo -bar - baz --> -. -<!-- Foo -bar - baz --> -. - -A processing instruction: - -. -<?php - echo 'foo' -?> -. -<?php - echo 'foo' -?> -. - -CDATA: - -. -<![CDATA[ -function matchwo(a,b) -{ -if (a < b && a < 0) then - { - return 1; - } -else - { - return 0; - } -} -]]> -. -<![CDATA[ -function matchwo(a,b) -{ -if (a < b && a < 0) then - { - return 1; - } -else - { - return 0; - } -} -]]> -. - -The opening tag can be indented 1-3 spaces, but not 4: - -. - <!-- foo --> - - <!-- foo --> -. - <!-- foo --> -<pre><code><!-- foo --> -</code></pre> -. - -An HTML block can interrupt a paragraph, and need not be preceded -by a blank line. - -. -Foo -<div> -bar -</div> -. -<p>Foo</p> -<div> -bar -</div> -. - -However, a following blank line is always needed, except at the end of -a document: - -. -<div> -bar -</div> -*foo* -. -<div> -bar -</div> -*foo* -. - -An incomplete HTML block tag may also start an HTML block: - -. -<div class -foo -. -<div class -foo -. - -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. - -Indeed, most Markdown implementations, including some of Gruber's -own perl implementations, do not impose these restrictions. - -There is one respect, however, in which Gruber's rule is more liberal -than the one given here, since it allows blank lines to occur inside -an HTML block. There are two reasons for disallowing them here. -First, it removes the need to parse balanced tags, which is -expensive and can require backtracking from the end of the document -if no matching end tag is found. Second, it provides a very simple -and flexible way of including Markdown content inside HTML tags: -simply separate the Markdown from the HTML using blank lines: - -. -<div> - -*Emphasized* text. - -</div> -. -<div> -<p><em>Emphasized</em> text.</p> -</div> -. - -Compare: - -. -<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: - -. -<table> - -<tr> - -<td> -Hi -</td> - -</tr> - -</table> -. -<table> -<tr> -<td> -Hi -</td> -</tr> -</table> -. - -Moreover, blank lines are usually not necessary and can be -deleted. The exception is inside `<pre>` tags; here, one can -replace the blank lines with ` ` entities. - -So there is no important loss of expressive power with the new rule. - -## Link reference definitions - -A [link reference definition](#link-reference-definition) -<a id="link-reference-definition"></a> consists of a [link -label](#link-label), indented up to three spaces, followed -by a colon (`:`), optional blank space (including up to one -newline), a [link destination](#link-destination), optional -blank space (including up to one newline), and an optional [link -title](#link-title), which if it is present must be separated -from the [link destination](#link-destination) by whitespace. -No further non-space characters may occur on the line. - -A [link reference-definition](#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](#reference-link) -and reference-style [images](#image) elsewhere in the document. [Link -reference definitions] can come either before or after the links that use -them. - -. -[foo]: /url "title" - -[foo] -. -<p><a href="/url" title="title">foo</a></p> -. - -. - [foo]: - /url - 'the title' - -[foo] -. -<p><a href="/url" title="the title">foo</a></p> -. - -. -[Foo*bar\]]:my_(url) 'title (with parens)' - -[Foo*bar\]] -. -<p><a href="my_(url)" title="title (with parens)">Foo*bar]</a></p> -. - -. -[Foo bar]: -<my url> -'title' - -[Foo bar] -. -<p><a href="my%20url" title="title">Foo bar</a></p> -. - -The title may be omitted: - -. -[foo]: -/url - -[foo] -. -<p><a href="/url">foo</a></p> -. - -The link destination may not be omitted: - -. -[foo]: - -[foo] -. -<p>[foo]:</p> -<p>[foo]</p> -. - -A link can come before its corresponding definition: - -. -[foo] - -[foo]: url -. -<p><a href="url">foo</a></p> -. - -If there are several matching definitions, the first one takes -precedence: - -. -[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](#matches)). - -. -[FOO]: /url - -[Foo] -. -<p><a href="/url">Foo</a></p> -. - -. -[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. - -. -[foo]: /url -. -. - -This is not a link reference definition, because there are -non-space characters after the title: - -. -[foo]: /url "title" ok -. -<p>[foo]: /url "title" ok</p> -. - -This is not a link reference definition, because it is indented -four spaces: - -. - [foo]: /url "title" - -[foo] -. -<pre><code>[foo]: /url "title" -</code></pre> -<p>[foo]</p> -. - -This is not a link reference definition, because it occurs inside -a code block: - -. -``` -[foo]: /url -``` - -[foo] -. -<pre><code>[foo]: /url -</code></pre> -<p>[foo]</p> -. - -A [link reference definition](#link-reference-definition) cannot -interrupt a paragraph. - -. -Foo -[bar]: /baz - -[bar] -. -<p>Foo -[bar]: /baz</p> -<p>[bar]</p> -. - -However, it can directly follow other block elements, such as headers -and horizontal rules, and it need not be followed by a blank line. - -. -# [Foo] -[foo]: /url -> bar -. -<h1><a href="/url">Foo</a></h1> -<blockquote> -<p>bar</p> -</blockquote> -. - -Several [link references](#link-reference) can occur one after another, -without intervening blank lines. - -. -[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](#link-reference-definition) can occur -inside block containers, like lists and block quotations. They -affect the entire document, not just the container in which they -are defined: - -. -[foo] - -> [foo]: /url -. -<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](#paragraph).<a id="paragraph"></a> -The contents of the paragraph are the result of parsing the -paragraph's raw content as inlines. The paragraph's raw content -is formed by concatenating the lines and removing initial and final -spaces. - -A simple example with two paragraphs: - -. -aaa - -bbb -. -<p>aaa</p> -<p>bbb</p> -. - -Paragraphs can contain multiple lines, but no blank lines: - -. -aaa -bbb - -ccc -ddd -. -<p>aaa -bbb</p> -<p>ccc -ddd</p> -. - -Multiple blank lines between paragraph have no effect: - -. -aaa - - -bbb -. -<p>aaa</p> -<p>bbb</p> -. - -Leading spaces are skipped: - -. - aaa - bbb -. -<p>aaa -bbb</p> -. - -Lines after the first may be indented any amount, since indented -code blocks cannot interrupt paragraphs. - -. -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: - -. - aaa -bbb -. -<p>aaa -bbb</p> -. - -. - 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: - -. -aaa -bbb -. -<p>aaa<br /> -bbb</p> -. - -## Blank lines - -[Blank lines](#blank-line) between block-level elements are ignored, -except for the role they play in determining whether a [list](#list) -is [tight](#tight) or [loose](#loose). - -Blank lines at the beginning and end of the document are also ignored. - -. - - -aaa - - -# aaa - - -. -<p>aaa</p> -<h1>aaa</h1> -. - - -# Container blocks - -A [container block](#container-block) is a block that has other -blocks as its contents. There are two basic kinds of container blocks: -[block quotes](#block-quote) and [list items](#list-item). -[Lists](#list) are meta-containers for [list items](#list-item). - -We define the syntax for container blocks recursively. The general -form of the definition is: - -> If X is a sequence of blocks, then the result of -> transforming X in such-and-such a way is a container of type Y -> with these blocks as its content. - -So, we explain what counts as a block quote or list item by explaining -how these can be *generated* from their contents. This should suffice -to define the syntax, although it does not give a recipe for *parsing* -these constructions. (A recipe is provided below in the section entitled -[A parsing strategy](#appendix-a-a-parsing-strategy).) - -## Block quotes - -A [block quote marker](#block-quote-marker) <a id="block-quote-marker"></a> -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](#block-quote): -<a id="block-quote"></a> - -1. **Basic case.** If a string of lines *Ls* constitute a sequence - of blocks *Bs*, then the result of appending a [block quote - marker](#block-quote-marker) to the beginning of each line in *Ls* - is a [block quote](#block-quote) containing *Bs*. - -2. **Laziness.** If a string of lines *Ls* constitute a [block - quote](#block-quote) with contents *Bs*, then the result of deleting - the initial [block quote marker](#block-quote-marker) from one or - more lines in which the next non-space character after the [block - quote marker](#block-quote-marker) is [paragraph continuation - text](#paragraph-continuation-text) is a block quote with *Bs* as - its content. <a id="paragraph-continuation-text"></a> - [Paragraph continuation text](#paragraph-continuation-text) is text - that will be parsed as part of the content of a paragraph, but does - not occur at the beginning of the paragraph. - -3. **Consecutiveness.** A document cannot contain two [block - quotes](#block-quote) in a row unless there is a [blank - line](#blank-line) between them. - -Nothing else counts as a [block quote](#block-quote). - -Here is a simple example: - -. -> # Foo -> bar -> baz -. -<blockquote> -<h1>Foo</h1> -<p>bar -baz</p> -</blockquote> -. - -The spaces after the `>` characters can be omitted: - -. -># Foo ->bar -> baz -. -<blockquote> -<h1>Foo</h1> -<p>bar -baz</p> -</blockquote> -. - -The `>` characters can be indented 1-3 spaces: - -. - > # Foo - > bar - > baz -. -<blockquote> -<h1>Foo</h1> -<p>bar -baz</p> -</blockquote> -. - -Four spaces gives us a code block: - -. - > # Foo - > bar - > baz -. -<pre><code>> # Foo -> bar -> baz -</code></pre> -. - -The Laziness clause allows us to omit the `>` before a -paragraph continuation line: - -. -> # 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: - -. -> bar -baz -> foo -. -<blockquote> -<p>bar -baz -foo</p> -</blockquote> -. - -Laziness only applies to lines that are continuations of -paragraphs. Lines containing characters or indentation that indicate -block structure cannot be lazy. - -. -> foo ---- -. -<blockquote> -<p>foo</p> -</blockquote> -<hr /> -. - -. -> - foo -- bar -. -<blockquote> -<ul> -<li>foo</li> -</ul> -</blockquote> -<ul> -<li>bar</li> -</ul> -. - -. -> foo - bar -. -<blockquote> -<pre><code>foo -</code></pre> -</blockquote> -<pre><code>bar -</code></pre> -. - -. -> ``` -foo -``` -. -<blockquote> -<pre><code></code></pre> -</blockquote> -<p>foo</p> -<pre><code></code></pre> -. - -A block quote can be empty: - -. -> -. -<blockquote> -</blockquote> -. - -. -> -> -> -. -<blockquote> -</blockquote> -. - -A block quote can have initial or final blank lines: - -. -> -> foo -> -. -<blockquote> -<p>foo</p> -</blockquote> -. - -A blank line always separates block quotes: - -. -> 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: - -. -> foo -> bar -. -<blockquote> -<p>foo -bar</p> -</blockquote> -. - -To get a block quote with two paragraphs, use: - -. -> foo -> -> bar -. -<blockquote> -<p>foo</p> -<p>bar</p> -</blockquote> -. - -Block quotes can interrupt paragraphs: - -. -foo -> bar -. -<p>foo</p> -<blockquote> -<p>bar</p> -</blockquote> -. - -In general, blank lines are not needed before or after block -quotes: - -. -> 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: - -. -> bar -baz -. -<blockquote> -<p>bar -baz</p> -</blockquote> -. - -. -> bar - -baz -. -<blockquote> -<p>bar</p> -</blockquote> -<p>baz</p> -. - -. -> 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: - -. -> > > foo -bar -. -<blockquote> -<blockquote> -<blockquote> -<p>foo -bar</p> -</blockquote> -</blockquote> -</blockquote> -. - -. ->>> 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](#block-quote-marker) includes -both the `>` and a following space. So *five spaces* are needed after -the `>`: - -. -> code - -> not code -. -<blockquote> -<pre><code>code -</code></pre> -</blockquote> -<blockquote> -<p>not code</p> -</blockquote> -. - - -## List items - -A [list marker](#list-marker) <a id="list-marker"></a> is a -[bullet list marker](#bullet-list-marker) or an [ordered list -marker](#ordered-list-marker). - -A [bullet list marker](#bullet-list-marker) <a id="bullet-list-marker"></a> -is a `-`, `+`, or `*` character. - -An [ordered list marker](#ordered-list-marker) <a id="ordered-list-marker"></a> -is a sequence of one of more digits (`0-9`), followed by either a -`.` character or a `)` character. - -The following rules define [list items](#list-item): - -1. **Basic case.** If a sequence of lines *Ls* constitute a sequence of - blocks *Bs* starting with a non-space character and not separated - from each other by more than one blank line, and *M* is a list - marker *M* of width *W* followed by 0 < *N* < 5 spaces, then the result - of prepending *M* and the following spaces to the first line of - *Ls*, and indenting subsequent lines of *Ls* by *W + N* spaces, is a - list item with *Bs* as its contents. The type of the list item - (bullet or ordered) is determined by the type of its list marker. - If the list item is ordered, then it is also assigned a start - number, based on the ordered list marker. - -For example, let *Ls* be the lines - -. -A paragraph -with two lines. - - indented code - -> A block quote. -. -<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*: - -. -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 nonspace character, then blocks -must be indented five spaces in order to fall under the list -item. - -Here are some examples showing how far content must be indented to be -put under the list item: - -. -- one - - two -. -<ul> -<li>one</li> -</ul> -<p>two</p> -. - -. -- one - - two -. -<ul> -<li><p>one</p> -<p>two</p></li> -</ul> -. - -. - - one - - two -. -<ul> -<li>one</li> -</ul> -<pre><code> two -</code></pre> -. - -. - - 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 nonspace -character after the list marker. However, that is not quite right. -The spaces after the list marker determine how much relative indentation -is needed. Which column this indentation reaches will depend on -how the list item is embedded in other constructions, as shown by -this example: - -. - > > 1. one ->> ->> two -. -<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 -sufficent indentation after the last containing blockquote marker. - -The converse is also possible. In the following example, the word `two` -occurs far to the right of the initial text of the list item, `one`, but -it is not considered part of the list item, because it is not indented -far enough past the blockquote marker: - -. ->>- one ->> - > > two -. -<blockquote> -<blockquote> -<ul> -<li>one</li> -</ul> -<p>two</p> -</blockquote> -</blockquote> -. - -A list item may not contain blocks that are separated by more than -one blank line. Thus, two blank lines will end a list, unless the -two blanks are contained in a [fenced code block](#fenced-code-block). - -. -- foo - - bar - -- foo - - - bar - -- ``` - foo - - - bar - ``` -. -<ul> -<li><p>foo</p> -<p>bar</p></li> -<li><p>foo</p></li> -</ul> -<p>bar</p> -<ul> -<li><pre><code>foo - - -bar -</code></pre></li> -</ul> -. - -A list item may contain any kind of block: - -. -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> -. - -2. **Item starting with indented code.** If a sequence of lines *Ls* - constitute a sequence of blocks *Bs* starting with an indented code - block and not separated from each other by more than one blank line, - and *M* is a list marker *M* of width *W* followed by - one space, then the result of prepending *M* and the following - space to the first line of *Ls*, and indenting subsequent lines of - *Ls* by *W + 1* spaces, is a list item with *Bs* as its contents. - If a line is empty, then it need not be indented. The type of the - list item (bullet or ordered) is determined by the type of its list - marker. If the list item is ordered, then it is also assigned a - start number, based on the ordered list marker. - -An indented code block will have to be indented four spaces beyond -the edge of the region where text will be included in the list item. -In the following case that is 6 spaces: - -. -- foo - - bar -. -<ul> -<li><p>foo</p> -<pre><code>bar -</code></pre></li> -</ul> -. - -And in this case it is 11 spaces: - -. - 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: - -. - indented code - -paragraph - - more code -. -<pre><code>indented code -</code></pre> -<p>paragraph</p> -<pre><code>more code -</code></pre> -. - -. -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: - -. -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 nonspace -character, and (b) cases in which they begin with an indented code -block. In a case like the following, where the first block begins with -a three-space indent, the rules do not allow us to form a list item by -indenting the whole thing and prepending a list marker: - -. - foo - -bar -. -<p>foo</p> -<p>bar</p> -. - -. -- 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: - -. -- foo - - bar -. -<ul> -<li><p>foo</p> -<p>bar</p></li> -</ul> -. - - -3. **Indentation.** If a sequence of lines *Ls* constitutes a list item - according to rule #1 or #2, then the result of indenting each line - of *L* by 1-3 spaces (the same for each line) also constitutes a - list item with the same contents and attributes. If a line is - empty, then it need not be indented. - -Indented one space: - -. - 1. A paragraph - with two lines. - - indented code - - > A block quote. -. -<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: - -. - 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: - -. - 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: - -. - 1. A paragraph - with two lines. - - indented code - - > A block quote. -. -<pre><code>1. A paragraph - with two lines. - - indented code - - > A block quote. -</code></pre> -. - - -4. **Laziness.** If a string of lines *Ls* constitute a [list - item](#list-item) with contents *Bs*, then the result of deleting - some or all of the indentation from one or more lines in which the - next non-space character after the indentation is - [paragraph continuation text](#paragraph-continuation-text) is a - list item with the same contents and attributes. - -Here is an example with lazy continuation lines: - -. - 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: - -. - 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: - -. -> 1. > Blockquote -continued here. -. -<blockquote> -<ol> -<li><blockquote> -<p>Blockquote -continued here.</p> -</blockquote></li> -</ol> -</blockquote> -. - -. -> 1. > Blockquote -> continued here. -. -<blockquote> -<ol> -<li><blockquote> -<p>Blockquote -continued here.</p> -</blockquote></li> -</ol> -</blockquote> -. - - -5. **That's all.** Nothing that is not counted as a list item by rules - #1--4 counts as a [list item](#list-item). - -The rules for sublists follow from the general rules above. A sublist -must be indented the same number of spaces a paragraph would need to be -in order to be included in the list item. - -So, in this case we need two spaces indent: - -. -- foo - - bar - - baz -. -<ul> -<li>foo -<ul> -<li>bar -<ul> -<li>baz</li> -</ul></li> -</ul></li> -</ul> -. - -One is not enough: - -. -- foo - - bar - - baz -. -<ul> -<li>foo</li> -<li>bar</li> -<li>baz</li> -</ul> -. - -Here we need four, because the list marker is wider: - -. -10) foo - - bar -. -<ol start="10"> -<li>foo -<ul> -<li>bar</li> -</ul></li> -</ol> -. - -Three is not enough: - -. -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: - -. -- - foo -. -<ul> -<li><ul> -<li>foo</li> -</ul></li> -</ul> -. - -. -1. - 2. foo -. -<ol> -<li><ul> -<li><ol start="2"> -<li>foo</li> -</ol></li> -</ul></li> -</ol> -. - -A list item may be empty: - -. -- foo -- -- bar -. -<ul> -<li>foo</li> -<li></li> -<li>bar</li> -</ul> -. - -. -- -. -<ul> -<li></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, #4, 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](#list) <a id="list"></a> is a sequence of one or more -list items [of the same type](#of-the-same-type). The list items -may be separated by single [blank lines](#blank-line), but two -blank lines end all containing lists. - -Two list items are [of the same type](#of-the-same-type) -<a id="of-the-same-type"></a> if they begin with a [list -marker](#list-marker) of the same type. Two list markers are of the -same type if (a) they are bullet list markers using the same character -(`-`, `+`, or `*`) or (b) they are ordered list numbers with the same -delimiter (either `.` or `)`). - -A list is an [ordered list](#ordered-list) <a id="ordered-list"></a> -if its constituent list items begin with -[ordered list markers](#ordered-list-marker), and a [bullet -list](#bullet-list) <a id="bullet-list"></a> if its constituent list -items begin with [bullet list markers](#bullet-list-marker). - -The [start number](#start-number) <a id="start-number"></a> -of an [ordered list](#ordered-list) is determined by the list number of -its initial list item. The numbers of subsequent list items are -disregarded. - -A list is [loose](#loose) if it any of its constituent list items are -separated by blank lines, or if any of its constituent list items -directly contain two block-level elements with a blank line between -them. Otherwise a list is [tight](#tight). (The difference in HTML output -is that paragraphs in a loose with are wrapped in `<p>` tags, while -paragraphs in a tight list are not.) - -Changing the bullet or ordered list delimiter starts a new list: - -. -- foo -- bar -+ baz -. -<ul> -<li>foo</li> -<li>bar</li> -</ul> -<ul> -<li>baz</li> -</ul> -. - -. -1. foo -2. bar -3) baz -. -<ol> -<li>foo</li> -<li>bar</li> -</ol> -<ol start="3"> -<li>baz</li> -</ol> -. - -There can be blank lines between items, but two blank lines end -a list: - -. -- foo - -- bar - - -- baz -. -<ul> -<li><p>foo</p></li> -<li><p>bar</p></li> -</ul> -<ul> -<li>baz</li> -</ul> -. - -As illustrated above in the section on [list items](#list-item), -two blank lines between blocks *within* a list item will also end a -list: - -. -- foo - - - bar -- baz -. -<ul> -<li>foo</li> -</ul> -<p>bar</p> -<ul> -<li>baz</li> -</ul> -. - -Indeed, two blank lines will end *all* containing lists: - -. -- foo - - bar - - baz - - - bim -. -<ul> -<li>foo -<ul> -<li>bar -<ul> -<li>baz</li> -</ul></li> -</ul></li> -</ul> -<pre><code> bim -</code></pre> -. - -Thus, two blank lines can be used to separate consecutive lists of -the same type, or to separate a list from an indented code block -that would otherwise be parsed as a subparagraph of the final list -item: - -. -- foo -- bar - - -- baz -- bim -. -<ul> -<li>foo</li> -<li>bar</li> -</ul> -<ul> -<li>baz</li> -<li>bim</li> -</ul> -. - -. -- 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: - -. -- a - - b - - c - - d - - e - - f -- g -. -<ul> -<li>a</li> -<li>b</li> -<li>c</li> -<li>d</li> -<li>e</li> -<li>f</li> -<li>g</li> -</ul> -. - -This is a loose list, because there is a blank line between -two of the list items: - -. -- 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: - -. -* 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: - -. -- a -- b - - c -- d -. -<ul> -<li><p>a</p></li> -<li><p>b</p> -<p>c</p></li> -<li><p>d</p></li> -</ul> -. - -. -- 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: - -. -- 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 inner list is loose while -the other list is tight: - -. -- 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: - -. -* 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: - -. -- 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: - -. -- a -. -<ul> -<li>a</li> -</ul> -. - -. -- a - - b -. -<ul> -<li>a -<ul> -<li>b</li> -</ul></li> -</ul> -. - -Here the outer list is loose, the inner list tight: - -. -* foo - * bar - - baz -. -<ul> -<li><p>foo</p> -<ul> -<li>bar</li> -</ul> -<p>baz</p></li> -</ul> -. - -. -- 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 - -. -`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: - -. -\!\"\#\$\%\&\'\(\)\*\+\,\-\.\/\:\;\<\=\>\?\@\[\\\]\^\_\`\{\|\}\~ -. -<p>!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~</p> -. - -Backslashes before other characters are treated as literal -backslashes: - -. -\→\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: - -. -\*not emphasized* -\<br/> not a tag -\[not a link](/foo) -\`not code` -1\. not a list -\* not a list -\# not a header -\[foo]: /url "not a reference" -. -<p>*not emphasized* -<br/> not a tag -[not a link](/foo) -`not code` -1. not a list -* not a list -# not a header -[foo]: /url "not a reference"</p> -. - -If a backslash is itself escaped, the following character is not: - -. -\\*emphasis* -. -<p>\<em>emphasis</em></p> -. - -A backslash at the end of the line is a hard line break: - -. -foo\ -bar -. -<p>foo<br /> -bar</p> -. - -Backslash escapes do not work in code blocks, code spans, autolinks, or -raw HTML: - -. -`` \[\` `` -. -<p><code>\[\`</code></p> -. - -. - \[\] -. -<pre><code>\[\] -</code></pre> -. - -. -~~~ -\[\] -~~~ -. -<pre><code>\[\] -</code></pre> -. - -. -<https://google.com?find=\*> -. -<p><a href="https://google.com?find=%5C*">https://google.com?find=\*</a></p> -. - -. -<a href="/bar\/)"> -. -<p><a href="/bar\/)"></p> -. - -But they work in all other contexts, including URLs and link titles, -link references, and info strings in [fenced code -blocks](#fenced-code-block): - -. -[foo](/bar\* "ti\*tle") -. -<p><a href="/bar*" title="ti*tle">foo</a></p> -. - -. -[foo] - -[foo]: /bar\* "ti\*tle" -. -<p><a href="/bar*" title="ti*tle">foo</a></p> -. - -. -``` foo\+bar -foo -``` -. -<pre><code class="language-foo+bar">foo -</code></pre> -. - - -## Entities - -With the goal of making this standard as HTML-agnostic as possible, all HTML valid HTML Entities in any -context are recognized as such and converted into their actual values (i.e. the UTF8 characters representing -the entity itself) before they are stored in the AST. - -This allows implementations that target HTML output to trivially escape the entities when generating HTML, -and simplifies the job of implementations targetting other languages, as these will only need to handle the -UTF8 chars and need not be HTML-entity aware. - -[Named entities](#name-entities) <a id="named-entities"></a> consist of `&` -+ any of the valid HTML5 entity names + `;`. The [following document](https://www.whatwg.org/specs/web-apps/current-work/multipage/entities.json) -is used as an authoritative source of the valid entity names and their corresponding codepoints. - -Conforming implementations that target Markdown don't need to generate entities for all the valid -named entities that exist, with the exception of `"` (`"`), `&` (`&`), `<` (`<`) and `>` (`>`), -which always need to be written as entities for security reasons. - -. - & © Æ Ď ¾ ℋ ⅆ ∲ -. -<p> & © Æ Ď ¾ ℋ ⅆ ∲</p> -. - -[Decimal entities](#decimal-entities) <a id="decimal-entities"></a> -consist of `&#` + a string of 1--8 arabic digits + `;`. Again, these entities need to be recognised -and tranformed into their corresponding UTF8 codepoints. Invalid Unicode codepoints will be written -as the "unknown codepoint" character (`0xFFFD`) - -. -# Ӓ Ϡ � -. -<p># Ӓ Ϡ �</p> -. - -[Hexadecimal entities](#hexadecimal-entities) <a id="hexadecimal-entities"></a> -consist of `&#` + either `X` or `x` + a string of 1-8 hexadecimal digits -+ `;`. They will also be parsed and turned into their corresponding UTF8 values in the AST. - -. -" ആ ಫ -. -<p>" ആ ಫ</p> -. - -Here are some nonentities: - -. -  &x; &#; &#x; &ThisIsWayTooLongToBeAnEntityIsntIt; &hi?; -. -<p>&nbsp &x; &#; &#x; &ThisIsWayTooLongToBeAnEntityIsntIt; &hi?;</p> -. - -Although HTML5 does accept some entities without a trailing semicolon -(such as `©`), these are not recognized as entities here, because it makes the grammar too ambiguous: - -. -© -. -<p>&copy</p> -. - -Strings that are not on the list of HTML5 named entities are not recognized as entities either: - -. -&MadeUpEntity; -. -<p>&MadeUpEntity;</p> -. - -Entities are recognized in any context besides code spans or -code blocks, including raw HTML, URLs, [link titles](#link-title), and -[fenced code block](#fenced-code-block) info strings: - -. -<a href="öö.html"> -. -<p><a href="öö.html"></p> -. - -. -[foo](/föö "föö") -. -<p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p> -. - -. -[foo] - -[foo]: /föö "föö" -. -<p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p> -. - -. -``` föö -foo -``` -. -<pre><code class="language-föö">foo -</code></pre> -. - -Entities are treated as literal text in code spans and code blocks: - -. -`föö` -. -<p><code>f&ouml;&ouml;</code></p> -. - -. - föfö -. -<pre><code>f&ouml;f&ouml; -</code></pre> -. - -## Code span - -A [backtick string](#backtick-string) <a id="backtick-string"></a> -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 newlines removed, and consecutive spaces and newlines -collapsed to single spaces. - -This is a simple code span: - -. -`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: - -. -`` foo ` bar `` -. -<p><code>foo ` bar</code></p> -. - -This example shows the motivation for stripping leading and trailing -spaces: - -. -` `` ` -. -<p><code>``</code></p> -. - -Newlines are treated like spaces: - -. -`` -foo -`` -. -<p><code>foo</code></p> -. - -Interior spaces and newlines are collapsed into single spaces, just -as they would be by a browser: - -. -`foo bar - baz` -. -<p><code>foo bar baz</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 newlines. Some, including `Markdown.pl` and -`showdown`, convert an internal newline 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.) - -. -`foo `` bar` -. -<p><code>foo `` bar</code></p> -. - -Note that backslash escapes do not work in code spans. All backslashes -are treated literally: - -. -`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: - -. -*foo`*` -. -<p>*foo<code>*</code></p> -. - -And this is not parsed as a link: - -. -[not a `link](/foo`) -. -<p>[not a <code>link](/foo</code>)</p> -. - -But this is a link: - -. -<https://foo.bar.`baz>` -. -<p><a href="https://foo.bar.%60baz">https://foo.bar.`baz</a>`</p> -. - -And this is an HTML tag: - -. -<a href="`">` -. -<p><a href="`">`</p> -. - -When a backtick string is not closed by a matching backtick string, -we just have literal backticks: - -. -```foo`` -. -<p>```foo``</p> -. - -. -`foo -. -<p>`foo</p> -. - -## Emphasis and strong emphasis - -John Gruber's original [Markdown syntax -description](https://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 following rules capture all of these patterns, while allowing -for efficient parsing strategies that do not backtrack: - -1. A single `*` character [can open emphasis](#can-open-emphasis) - <a id="can-open-emphasis"></a> iff - - (a) it is not part of a sequence of four or more unescaped `*`s, - (b) it is not followed by whitespace, and - (c) either it is not followed by a `*` character or it is - followed immediately by strong emphasis. - -2. A single `_` character [can open emphasis](#can-open-emphasis) iff - - (a) it is not part of a sequence of four or more unescaped `_`s, - (b) it is not followed by whitespace, - (c) it is not preceded by an ASCII alphanumeric character, and - (d) either it is not followed by a `_` character or it is - followed immediately by strong emphasis. - -3. A single `*` character [can close emphasis](#can-close-emphasis) - <a id="can-close-emphasis"></a> iff - - (a) it is not part of a sequence of four or more unescaped `*`s, and - (b) it is not preceded by whitespace. - -4. A single `_` character [can close emphasis](#can-close-emphasis) iff - - (a) it is not part of a sequence of four or more unescaped `_`s, - (b) it is not preceded by whitespace, and - (c) it is not followed by an ASCII alphanumeric character. - -5. A double `**` [can open strong emphasis](#can-open-strong-emphasis) - <a id="can-open-strong-emphasis" ></a> iff - - (a) it is not part of a sequence of four or more unescaped `*`s, - (b) it is not followed by whitespace, and - (c) either it is not followed by a `*` character or it is - followed immediately by emphasis. - -6. A double `__` [can open strong emphasis](#can-open-strong-emphasis) - iff - - (a) it is not part of a sequence of four or more unescaped `_`s, - (b) it is not followed by whitespace, and - (c) it is not preceded by an ASCII alphanumeric character, and - (d) either it is not followed by a `_` character or it is - followed immediately by emphasis. - -7. A double `**` [can close strong emphasis](#can-close-strong-emphasis) - <a id="can-close-strong-emphasis" ></a> iff - - (a) it is not part of a sequence of four or more unescaped `*`s, and - (b) it is not preceded by whitespace. - -8. A double `__` [can close strong emphasis](#can-close-strong-emphasis) - iff - - (a) it is not part of a sequence of four or more unescaped `_`s, - (b) it is not preceded by whitespace, and - (c) it is not followed by an ASCII alphanumeric character. - -9. Emphasis begins with a delimiter that [can open - emphasis](#can-open-emphasis) and includes inlines parsed - sequentially until a delimiter that [can close - emphasis](#can-close-emphasis), and that uses the same - character (`_` or `*`) as the opening delimiter, is reached. - -10. Strong emphasis begins with a delimiter that [can open strong - emphasis](#can-open-strong-emphasis) and includes inlines parsed - sequentially until a delimiter that [can close strong - emphasis](#can-close-strong-emphasis), and that uses the - same character (`_` or `*`) as the opening delimiter, is reached. - -These rules can be illustrated through a series of examples. - -Simple emphasis: - -. -*foo bar* -. -<p><em>foo bar</em></p> -. - -. -_foo bar_ -. -<p><em>foo bar</em></p> -. - -Simple strong emphasis: - -. -**foo bar** -. -<p><strong>foo bar</strong></p> -. - -. -__foo bar__ -. -<p><strong>foo bar</strong></p> -. - -Emphasis can continue over line breaks: - -. -*foo -bar* -. -<p><em>foo -bar</em></p> -. - -. -_foo -bar_ -. -<p><em>foo -bar</em></p> -. - -. -**foo -bar** -. -<p><strong>foo -bar</strong></p> -. - -. -__foo -bar__ -. -<p><strong>foo -bar</strong></p> -. - -Emphasis can contain other inline constructs: - -. -*foo [bar](/url)* -. -<p><em>foo <a href="/url">bar</a></em></p> -. - -. -_foo [bar](/url)_ -. -<p><em>foo <a href="/url">bar</a></em></p> -. - -. -**foo [bar](/url)** -. -<p><strong>foo <a href="/url">bar</a></strong></p> -. - -. -__foo [bar](/url)__ -. -<p><strong>foo <a href="/url">bar</a></strong></p> -. - -Symbols contained in other inline constructs will not -close emphasis: - -. -*foo [bar*](/url) -. -<p>*foo <a href="/url">bar*</a></p> -. - -. -_foo [bar_](/url) -. -<p>_foo <a href="/url">bar_</a></p> -. - -. -**<a href="**"> -. -<p>**<a href="**"></p> -. - -. -__<a href="__"> -. -<p>__<a href="__"></p> -. - -. -*a `*`* -. -<p><em>a <code>*</code></em></p> -. - -. -_a `_`_ -. -<p><em>a <code>_</code></em></p> -. - -. -**a<https://foo.bar?q=**> -. -<p>**a<a href="https://foo.bar?q=**">https://foo.bar?q=**</a></p> -. - -. -__a<https://foo.bar?q=__> -. -<p>__a<a href="https://foo.bar?q=__">https://foo.bar?q=__</a></p> -. - -This is not emphasis, because the opening delimiter is -followed by white space: - -. -and * foo bar* -. -<p>and * foo bar*</p> -. - -. -_ foo bar_ -. -<p>_ foo bar_</p> -. - -. -and ** foo bar** -. -<p>and ** foo bar**</p> -. - -. -__ foo bar__ -. -<p>__ foo bar__</p> -. - -This is not emphasis, because the closing delimiter is -preceded by white space: - -. -and *foo bar * -. -<p>and *foo bar *</p> -. - -. -and _foo bar _ -. -<p>and _foo bar _</p> -. - -. -and **foo bar ** -. -<p>and **foo bar **</p> -. - -. -and __foo bar __ -. -<p>and __foo bar __</p> -. - -The rules imply that a sequence of four or more unescaped `*` or -`_` characters will always be parsed as a literal string: - -. -****hi**** -. -<p>****hi****</p> -. - -. -_____hi_____ -. -<p>_____hi_____</p> -. - -. -Sign here: _________ -. -<p>Sign here: _________</p> -. - -The rules also imply that there can be no empty emphasis or strong -emphasis: - -. -** is not an empty emphasis -. -<p>** is not an empty emphasis</p> -. - -. -**** is not an empty strong emphasis -. -<p>**** is not an empty strong emphasis</p> -. - -To include `*` or `_` in emphasized sections, use backslash escapes -or code spans: - -. -*here is a \** -. -<p><em>here is a *</em></p> -. - -. -__this is a double underscore (`__`)__ -. -<p><strong>this is a double underscore (<code>__</code>)</strong></p> -. - -`*` delimiters allow intra-word emphasis; `_` delimiters do not: - -. -foo*bar*baz -. -<p>foo<em>bar</em>baz</p> -. - -. -foo_bar_baz -. -<p>foo_bar_baz</p> -. - -. -foo__bar__baz -. -<p>foo__bar__baz</p> -. - -. -_foo_bar_baz_ -. -<p><em>foo_bar_baz</em></p> -. - -. -11*15*32 -. -<p>11<em>15</em>32</p> -. - -. -11_15_32 -. -<p>11_15_32</p> -. - -Internal underscores will be ignored in underscore-delimited -emphasis: - -. -_foo_bar_baz_ -. -<p><em>foo_bar_baz</em></p> -. - -. -__foo__bar__baz__ -. -<p><strong>foo__bar__baz</strong></p> -. - -The rules are sufficient for the following nesting patterns: - -. -***foo bar*** -. -<p><strong><em>foo bar</em></strong></p> -. - -. -___foo bar___ -. -<p><strong><em>foo bar</em></strong></p> -. - -. -***foo** bar* -. -<p><em><strong>foo</strong> bar</em></p> -. - -. -___foo__ bar_ -. -<p><em><strong>foo</strong> bar</em></p> -. - -. -***foo* bar** -. -<p><strong><em>foo</em> bar</strong></p> -. - -. -___foo_ bar__ -. -<p><strong><em>foo</em> bar</strong></p> -. - -. -*foo **bar*** -. -<p><em>foo <strong>bar</strong></em></p> -. - -. -_foo __bar___ -. -<p><em>foo <strong>bar</strong></em></p> -. - -. -**foo *bar*** -. -<p><strong>foo <em>bar</em></strong></p> -. - -. -__foo _bar___ -. -<p><strong>foo <em>bar</em></strong></p> -. - -. -*foo **bar*** -. -<p><em>foo <strong>bar</strong></em></p> -. - -. -_foo __bar___ -. -<p><em>foo <strong>bar</strong></em></p> -. - -. -*foo *bar* baz* -. -<p><em>foo <em>bar</em> baz</em></p> -. - -. -_foo _bar_ baz_ -. -<p><em>foo <em>bar</em> baz</em></p> -. - -. -**foo **bar** baz** -. -<p><strong>foo <strong>bar</strong> baz</strong></p> -. - -. -__foo __bar__ baz__ -. -<p><strong>foo <strong>bar</strong> baz</strong></p> -. - -. -*foo **bar** baz* -. -<p><em>foo <strong>bar</strong> baz</em></p> -. - -. -_foo __bar__ baz_ -. -<p><em>foo <strong>bar</strong> baz</em></p> -. - -. -**foo *bar* baz** -. -<p><strong>foo <em>bar</em> baz</strong></p> -. - -. -__foo _bar_ baz__ -. -<p><strong>foo <em>bar</em> baz</strong></p> -. - -Note that you cannot nest emphasis directly inside emphasis -using the same delimeter, or strong emphasis directly inside -strong emphasis: - -. -**foo** -. -<p><strong>foo</strong></p> -. - -. -****foo**** -. -<p>****foo****</p> -. - -For these nestings, you need to switch delimiters: - -. -*_foo_* -. -<p><em><em>foo</em></em></p> -. - -. -**__foo__** -. -<p><strong><strong>foo</strong></strong></p> -. - -Note that a `*` followed by a `*` can close emphasis, and -a `**` followed by a `*` can close strong emphasis (and -similarly for `_` and `__`): - -. -*foo** -. -<p><em>foo</em>*</p> -. - -. -*foo *bar** -. -<p><em>foo <em>bar</em></em></p> -. - -. -**foo*** -. -<p><strong>foo</strong>*</p> -. - -. -***foo* bar*** -. -<p><strong><em>foo</em> bar</strong>*</p> -. - -. -***foo** bar*** -. -<p><em><strong>foo</strong> bar</em>**</p> -. - -The following contains no strong emphasis, because the opening -delimiter is closed by the first `*` before `bar`: - -. -*foo**bar*** -. -<p><em>foo</em><em>bar</em>**</p> -. - -However, a string of four or more `****` can never close emphasis: - -. -*foo**** -. -<p>*foo****</p> -. - -Note that there are some asymmetries here: - -. -*foo** - -**foo* -. -<p><em>foo</em>*</p> -<p>**foo*</p> -. - -. -*foo *bar** - -**foo* bar* -. -<p><em>foo <em>bar</em></em></p> -<p>**foo* bar*</p> -. - -More cases with mismatched delimiters: - -. -**foo* bar* -. -<p>**foo* bar*</p> -. - -. -*bar*** -. -<p><em>bar</em>**</p> -. - -. -***foo* -. -<p>***foo*</p> -. - -. -**bar*** -. -<p><strong>bar</strong>*</p> -. - -. -***foo** -. -<p>***foo**</p> -. - -. -***foo *bar* -. -<p>***foo <em>bar</em></p> -. - -## Links - -A link contains a [link label](#link-label) (the visible text), -a [destination](#destination) (the URI that is the link destination), -and optionally a [link title](#link-title). There are two basic kinds -of links in Markdown. In [inline links](#inline-links) the destination -and title are given immediately after the label. In [reference -links](#reference-links) the destination and title are defined elsewhere -in the document. - -A [link label](#link-label) <a id="link-label"></a> consists of - -- an opening `[`, followed by -- zero or more backtick code spans, autolinks, HTML tags, link labels, - backslash-escaped ASCII punctuation characters, or non-`]` characters, - followed by -- a closing `]`. - -These rules are motivated by the following intuitive ideas: - -- A link label is a container for inline elements. -- The square brackets bind more tightly than emphasis markers, - but less tightly than `<>` or `` ` ``. -- Link labels may contain material in matching square brackets. - -A [link destination](#link-destination) <a id="link-destination"></a> -consists of either - -- a sequence of zero or more characters between an opening `<` and a - closing `>` that contains no line breaks or unescaped `<` or `>` - characters, or - -- a nonempty sequence of characters that does not include - ASCII space or control characters, and includes parentheses - only if (a) they are backslash-escaped or (b) they are part of - a balanced pair of unescaped parentheses that is not itself - inside a balanced pair of unescaped paretheses. - -A [link title](#link-title) <a id="link-title"></a> consists of either - -- a sequence of zero or more characters between straight double-quote - characters (`"`), including a `"` character only if it is - backslash-escaped, or - -- a sequence of zero or more characters between straight single-quote - characters (`'`), including a `'` character only if it is - backslash-escaped, or - -- a sequence of zero or more characters between matching parentheses - (`(...)`), including a `)` character only if it is backslash-escaped. - -An [inline link](#inline-link) <a id="inline-link"></a> -consists of a [link label](#link-label) followed immediately -by a left parenthesis `(`, optional whitespace, -an optional [link destination](#link-destination), -an optional [link title](#link-title) separated from the link -destination by whitespace, optional whitespace, and a right -parenthesis `)`. The link's text consists of the label (excluding -the enclosing square brackets) parsed as inlines. The link's -URI consists of the link destination, excluding enclosing `<...>` if -present, with backslash-escapes in effect as described above. The -link's title consists of the link title, excluding its enclosing -delimiters, with backslash-escapes in effect as described above. - -Here is a simple inline link: - -. -[link](/uri "title") -. -<p><a href="/uri" title="title">link</a></p> -. - -The title may be omitted: - -. -[link](/uri) -. -<p><a href="/uri">link</a></p> -. - -Both the title and the destination may be omitted: - -. -[link]() -. -<p><a href="">link</a></p> -. - -. -[link](<>) -. -<p><a href="">link</a></p> -. - - -If the destination contains spaces, it must be enclosed in pointy -braces: - -. -[link](/my uri) -. -<p>[link](/my uri)</p> -. - -. -[link](</my uri>) -. -<p><a href="/my%20uri">link</a></p> -. - -The destination cannot contain line breaks, even with pointy braces: - -. -[link](foo -bar) -. -<p>[link](foo -bar)</p> -. - -One level of balanced parentheses is allowed without escaping: - -. -[link]((foo)and(bar)) -. -<p><a href="(foo)and(bar)">link</a></p> -. - -However, if you have parentheses within parentheses, you need to escape -or use the `<...>` form: - -. -[link](foo(and(bar))) -. -<p>[link](foo(and(bar)))</p> -. - -. -[link](foo(and\(bar\))) -. -<p><a href="foo(and(bar))">link</a></p> -. - -. -[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: - -. -[link](foo\)\:) -. -<p><a href="foo):">link</a></p> -. - -URL-escaping and should be left alone inside the destination, as all URL-escaped characters -are also valid URL characters. HTML entities in the destination will be parsed into their UTF8 -codepoints, as usual, and optionally URL-escaped when written as HTML. - -. -[link](foo%20bä) -. -<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: - -. -[link]("title") -. -<p><a href="%22title%22">link</a></p> -. - -Titles may be in single quotes, double quotes, or parentheses: - -. -[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 entities may be used in titles: - -. -[link](/url "title \""") -. -<p><a href="/url" title="title """>link</a></p> -. - -Nested balanced quotes are not allowed without escaping: - -. -[link](/url "title "and" title") -. -<p>[link](/url "title "and" title")</p> -. - -But it is easy to work around this by using a different quote type: - -. -[link](/url 'title "and" title') -. -<p><a href="/url" title="title "and" 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, -entities, or using a different quote type for the enclosing title---to -write titles containing double quotes. `Markdown.pl`'s handling of -titles has a number of other strange features. For example, it allows -single-quoted titles in inline links, but not reference links. And, in -reference links but not inline links, it allows a title to begin with -`"` and end with `)`. `Markdown.pl` 1.0.1 even allows titles with no closing -quotation mark, though 1.0.2b8 does not. It seems preferable to adopt -a simple, rational rule that works the same way in inline links and -link reference definitions.) - -Whitespace is allowed around the destination and title: - -. -[link]( /uri - "title" ) -. -<p><a href="/uri" title="title">link</a></p> -. - -But it is not allowed between the link label and the -following parenthesis: - -. -[link] (/uri) -. -<p>[link] (/uri)</p> -. - -Note that this is not a link, because the closing `]` occurs in -an HTML tag: - -. -[foo <bar attr="](baz)"> -. -<p>[foo <bar attr="](baz)"></p> -. - - -There are three kinds of [reference links](#reference-link): -<a id="reference-link"></a> - -A [full reference link](#full-reference-link) <a id="full-reference-link"></a> -consists of a [link label](#link-label), optional whitespace, and -another [link label](#link-label) that [matches](#matches) a -[link reference definition](#link-reference-definition) elsewhere in the -document. - -One label [matches](#matches) <a id="matches"></a> -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](#link-reference-definition). - -Here is a simple example: - -. -[foo][bar] - -[bar]: /url "title" -. -<p><a href="/url" title="title">foo</a></p> -. - -The first label can contain inline content: - -. -[*foo\!*][bar] - -[bar]: /url "title" -. -<p><a href="/url" title="title"><em>foo!</em></a></p> -. - -Matching is case-insensitive: - -. -[foo][BaR] - -[bar]: /url "title" -. -<p><a href="/url" title="title">foo</a></p> -. - -Unicode case fold is used: - -. -[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: - -. -[Foo - bar]: /url - -[Baz][Foo bar] -. -<p><a href="/url">Baz</a></p> -. - -There can be whitespace between the two labels: - -. -[foo] [bar] - -[bar]: /url "title" -. -<p><a href="/url" title="title">foo</a></p> -. - -. -[foo] -[bar] - -[bar]: /url "title" -. -<p><a href="/url" title="title">foo</a></p> -. - -When there are multiple matching [link reference -definitions](#link-reference-definition), the first is used: - -. -[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: - -. -[bar][foo\!] - -[foo!]: /url -. -<p>[bar][foo!]</p> -. - -A [collapsed reference link](#collapsed-reference-link) -<a id="collapsed-reference-link"></a> consists of a [link -label](#link-label) that [matches](#matches) a [link reference -definition](#link-reference-definition) elsewhere in the -document, optional whitespace, and the string `[]`. The contents of the -first link label are parsed as inlines, which are used as the link's -text. The link's URI and title are provided by the matching reference -link definition. Thus, `[foo][]` is equivalent to `[foo][foo]`. - -. -[foo][] - -[foo]: /url "title" -. -<p><a href="/url" title="title">foo</a></p> -. - -. -[*foo* bar][] - -[*foo* bar]: /url "title" -. -<p><a href="/url" title="title"><em>foo</em> bar</a></p> -. - -The link labels are case-insensitive: - -. -[Foo][] - -[foo]: /url "title" -. -<p><a href="/url" title="title">Foo</a></p> -. - - -As with full reference links, whitespace is allowed -between the two sets of brackets: - -. -[foo] -[] - -[foo]: /url "title" -. -<p><a href="/url" title="title">foo</a></p> -. - -A [shortcut reference link](#shortcut-reference-link) -<a id="shortcut-reference-link"></a> consists of a [link -label](#link-label) that [matches](#matches) a [link reference -definition](#link-reference-definition) elsewhere in the -document and is not followed by `[]` or a link label. -The contents of the first link label are parsed as inlines, -which are used as the link's text. the link's URI and title -are provided by the matching link reference definition. -Thus, `[foo]` is equivalent to `[foo][]`. - -. -[foo] - -[foo]: /url "title" -. -<p><a href="/url" title="title">foo</a></p> -. - -. -[*foo* bar] - -[*foo* bar]: /url "title" -. -<p><a href="/url" title="title"><em>foo</em> bar</a></p> -. - -. -[[*foo* bar]] - -[*foo* bar]: /url "title" -. -<p>[<a href="/url" title="title"><em>foo</em> bar</a>]</p> -. - -The link labels are case-insensitive: - -. -[Foo] - -[foo]: /url "title" -. -<p><a href="/url" title="title">Foo</a></p> -. - -If you just want bracketed text, you can backslash-escape the -opening bracket to avoid links: - -. -\[foo] - -[foo]: /url "title" -. -<p>[foo]</p> -. - -Note that this is a link, because link labels bind more tightly -than emphasis: - -. -[foo*]: /url - -*[foo*] -. -<p>*<a href="/url">foo*</a></p> -. - -However, this is not, because link labels bind less -tightly than code backticks: - -. -[foo`]: /url - -[foo`]` -. -<p>[foo<code>]</code></p> -. - -Link labels can contain matched square brackets: - -. -[[[foo]]] - -[[[foo]]]: /url -. -<p><a href="/url">[[foo]]</a></p> -. - -. -[[[foo]]] - -[[[foo]]]: /url1 -[foo]: /url2 -. -<p><a href="/url1">[[foo]]</a></p> -. - -For non-matching brackets, use backslash escapes: - -. -[\[foo] - -[\[foo]: /url -. -<p><a href="/url">[foo</a></p> -. - -Full references take precedence over shortcut references: - -. -[foo][bar] - -[foo]: /url1 -[bar]: /url2 -. -<p><a href="/url2">foo</a></p> -. - -In the following case `[bar][baz]` is parsed as a reference, -`[foo]` as normal text: - -. -[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: - -. -[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): - -. -[foo][bar][baz] - -[baz]: /url1 -[foo]: /url2 -. -<p>[foo]<a href="/url1">bar</a></p> -. - - -## Images - -An (unescaped) exclamation mark (`!`) followed by a reference or -inline link will be parsed as an image. The link label will be -used as the image's alt text, and the link title, if any, will -be used as the image's title. - -. - -. -<p><img src="/url" alt="foo" title="title" /></p> -. - -. -![foo *bar*] - -[foo *bar*]: train.jpg "train & tracks" -. -<p><img src="train.jpg" alt="foo <em>bar</em>" title="train & tracks" /></p> -. - -. -![foo *bar*][] - -[foo *bar*]: train.jpg "train & tracks" -. -<p><img src="train.jpg" alt="foo <em>bar</em>" title="train & tracks" /></p> -. - -. -![foo *bar*][foobar] - -[FOOBAR]: train.jpg "train & tracks" -. -<p><img src="train.jpg" alt="foo <em>bar</em>" title="train & tracks" /></p> -. - -. - -. -<p><img src="train.jpg" alt="foo" /></p> -. - -. -My  -. -<p>My <img src="/path/to/train.jpg" alt="foo bar" title="title" /></p> -. - -. - -. -<p><img src="url" alt="foo" /></p> -. - -. - -. -<p><img src="/url" alt="" /></p> -. - -Reference-style: - -. -![foo] [bar] - -[bar]: /url -. -<p><img src="/url" alt="foo" /></p> -. - -. -![foo] [bar] - -[BAR]: /url -. -<p><img src="/url" alt="foo" /></p> -. - -Collapsed: - -. -![foo][] - -[foo]: /url "title" -. -<p><img src="/url" alt="foo" title="title" /></p> -. - -. -![*foo* bar][] - -[*foo* bar]: /url "title" -. -<p><img src="/url" alt="<em>foo</em> bar" title="title" /></p> -. - -The labels are case-insensitive: - -. -![Foo][] - -[foo]: /url "title" -. -<p><img src="/url" alt="Foo" title="title" /></p> -. - -As with full reference links, whitespace is allowed -between the two sets of brackets: - -. -![foo] -[] - -[foo]: /url "title" -. -<p><img src="/url" alt="foo" title="title" /></p> -. - -Shortcut: - -. -![foo] - -[foo]: /url "title" -. -<p><img src="/url" alt="foo" title="title" /></p> -. - -. -![*foo* bar] - -[*foo* bar]: /url "title" -. -<p><img src="/url" alt="<em>foo</em> bar" title="title" /></p> -. - -. -![[foo]] - -[[foo]]: /url "title" -. -<p><img src="/url" alt="[foo]" title="title" /></p> -. - -The link labels are case-insensitive: - -. -![Foo] - -[foo]: /url "title" -. -<p><img src="/url" alt="Foo" title="title" /></p> -. - -If you just want bracketed text, you can backslash-escape the -opening `!` and `[`: - -. -\!\[foo] - -[foo]: /url "title" -. -<p>![foo]</p> -. - -If you want a link after a literal `!`, backslash-escape the -`!`: - -. -\![foo] - -[foo]: /url "title" -. -<p>!<a href="/url" title="title">foo</a></p> -. - -## Autolinks - -Autolinks are absolute URIs and email addresses inside `<` and `>`. -They are parsed as links, with the URL or email address as the link -label. - -A [URI autolink](#uri-autolink) <a id="uri-autolink"></a> -consists of `<`, followed by an [absolute -URI](#absolute-uri) not containing `<`, followed by `>`. It is parsed -as a link to the URI, with the URI as the link's label. - -An [absolute URI](#absolute-uri), <a id="absolute-uri"></a> -for these purposes, consists of a [scheme](#scheme) followed by a colon (`:`) -followed by zero or more characters other than ASCII whitespace and -control characters, `<`, and `>`. If the URI includes these characters, -you must use percent-encoding (e.g. `%20` for a space). - -The following [schemes](#scheme) <a id="scheme"></a> -are recognized (case-insensitive): -`coap`, `doi`, `javascript`, `aaa`, `aaas`, `about`, `acap`, `cap`, -`cid`, `crid`, `data`, `dav`, `dict`, `dns`, `file`, `ftp`, `geo`, `go`, -`gopher`, `h323`, `http`, `https`, `iax`, `icap`, `im`, `imap`, `info`, -`ipp`, `iris`, `iris.beep`, `iris.xpc`, `iris.xpcs`, `iris.lwz`, `ldap`, -`mailto`, `mid`, `msrp`, `msrps`, `mtqp`, `mupdate`, `news`, `nfs`, -`ni`, `nih`, `nntp`, `opaquelocktoken`, `pop`, `pres`, `rtsp`, -`service`, `session`, `shttp`, `sieve`, `sip`, `sips`, `sms`, `snmp`,` -soap.beep`, `soap.beeps`, `tag`, `tel`, `telnet`, `tftp`, `thismessage`, -`tn3270`, `tip`, `tv`, `urn`, `vemmi`, `ws`, `wss`, `xcon`, -`xcon-userid`, `xmlrpc.beep`, `xmlrpc.beeps`, `xmpp`, `z39.50r`, -`z39.50s`, `adiumxtra`, `afp`, `afs`, `aim`, `apt`,` attachment`, `aw`, -`beshare`, `bitcoin`, `bolo`, `callto`, `chrome`,` chrome-extension`, -`com-eventbrite-attendee`, `content`, `cvs`,` dlna-playsingle`, -`dlna-playcontainer`, `dtn`, `dvb`, `ed2k`, `facetime`, `feed`, -`finger`, `fish`, `gg`, `git`, `gizmoproject`, `gtalk`, `hcp`, `icon`, -`ipn`, `irc`, `irc6`, `ircs`, `itms`, `jar`, `jms`, `keyparc`, `lastfm`, -`ldaps`, `magnet`, `maps`, `market`,` message`, `mms`, `ms-help`, -`msnim`, `mumble`, `mvn`, `notes`, `oid`, `palm`, `paparazzi`, -`platform`, `proxy`, `psyc`, `query`, `res`, `resource`, `rmi`, `rsync`, -`rtmp`, `secondlife`, `sftp`, `sgn`, `skype`, `smb`, `soldat`, -`spotify`, `ssh`, `steam`, `svn`, `teamspeak`, `things`, `udp`, -`unreal`, `ut2004`, `ventrilo`, `view-source`, `webcal`, `wtai`, -`wyciwyg`, `xfire`, `xri`, `ymsgr`. - -Here are some valid autolinks: - -. -<https://foo.bar.baz> -. -<p><a href="https://foo.bar.baz">https://foo.bar.baz</a></p> -. - -. -<https://foo.bar.baz?q=hello&id=22&boolean> -. -<p><a href="https://foo.bar.baz?q=hello&id=22&boolean">https://foo.bar.baz?q=hello&id=22&boolean</a></p> -. - -. -<irc://foo.bar:2233/baz> -. -<p><a href="irc://foo.bar:2233/baz">irc://foo.bar:2233/baz</a></p> -. - -Uppercase is also fine: - -. -<MAILTO:FOO@BAR.BAZ> -. -<p><a href="MAILTO:FOO@BAR.BAZ">MAILTO:FOO@BAR.BAZ</a></p> -. - -Spaces are not allowed in autolinks: - -. -<https://foo.bar/baz bim> -. -<p><https://foo.bar/baz bim></p> -. - -An [email autolink](#email-autolink) <a id="email-autolink"></a> -consists of `<`, followed by an [email address](#email-address), -followed by `>`. The link's label is the email address, -and the URL is `mailto:` followed by the email address. - -An [email address](#email-address), <a id="email-address"></a> -for these purposes, is anything that matches -the [non-normative regex from the HTML5 -spec](https://www.whatwg.org/specs/web-apps/current-work/multipage/forms.html#e-mail-state-%28type=email%29): - - /^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])? - (?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/ - -Examples of email autolinks: - -. -<foo@bar.baz.com> -. -<p><a href="mailto:foo@bar.baz.com">foo@bar.baz.com</a></p> -. - -. -<foo+special@Bar.baz-bar0.com> -. -<p><a href="mailto:foo+special@Bar.baz-bar0.com">foo+special@Bar.baz-bar0.com</a></p> -. - -These are not autolinks: - -. -<> -. -<p><></p> -. - -. -<heck://bing.bong> -. -<p><heck://bing.bong></p> -. - -. -< https://foo.bar > -. -<p>< https://foo.bar ></p> -. - -. -<foo.bar.baz> -. -<p><foo.bar.baz></p> -. - -. -<localhost:5001/foo> -. -<p><localhost:5001/foo></p> -. - -. -https://google.com -. -<p>https://google.com</p> -. - -. -foo@bar.baz.com -. -<p>foo@bar.baz.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](#tag-name) <a id="tag-name"></a> consists of an ASCII letter -followed by zero or more ASCII letters or digits. - -An [attribute](#attribute) <a id="attribute"></a> consists of whitespace, -an **attribute name**, and an optional **attribute value -specification**. - -An [attribute name](#attribute-name) <a id="attribute-name"></a> -consists of an ASCII letter, `_`, or `:`, followed by zero or more ASCII -letters, digits, `_`, `.`, `:`, or `-`. (Note: This is the XML -specification restricted to ASCII. HTML5 is laxer.) - -An [attribute value specification](#attribute-value-specification) -<a id="attribute-value-specification"></a> consists of optional whitespace, -a `=` character, optional whitespace, and an [attribute -value](#attribute-value). - -An [attribute value](#attribute-value) <a id="attribute-value"></a> -consists of an [unquoted attribute value](#unquoted-attribute-value), -a [single-quoted attribute value](#single-quoted-attribute-value), -or a [double-quoted attribute value](#double-quoted-attribute-value). - -An [unquoted attribute value](#unquoted-attribute-value) -<a id="unquoted-attribute-value"></a> is a nonempty string of characters not -including spaces, `"`, `'`, `=`, `<`, `>`, or `` ` ``. - -A [single-quoted attribute value](#single-quoted-attribute-value) -<a id="single-quoted-attribute-value"></a> consists of `'`, zero or more -characters not including `'`, and a final `'`. - -A [double-quoted attribute value](#double-quoted-attribute-value) -<a id="double-quoted-attribute-value"></a> consists of `"`, zero or more -characters not including `"`, and a final `"`. - -An [open tag](#open-tag) <a id="open-tag"></a> consists of a `<` character, -a [tag name](#tag-name), zero or more [attributes](#attribute), -optional whitespace, an optional `/` character, and a `>` character. - -A [closing tag](#closing-tag) <a id="closing-tag"></a> consists of the -string `</`, a [tag name](#tag-name), optional whitespace, and the -character `>`. - -An [HTML comment](#html-comment) <a id="html-comment"></a> consists of the -string `<!--`, a string of characters not including the string `--`, and -the string `-->`. - -A [processing instruction](#processing-instruction) -<a id="processing-instruction"></a> consists of the string `<?`, a string -of characters not including the string `?>`, and the string -`?>`. - -A [declaration](#declaration) <a id="declaration"></a> 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](#cdata-section) <a id="cdata-section"></a> consists of -the string `<![CDATA[`, a string of characters not including the string -`]]>`, and the string `]]>`. - -An [HTML tag](#html-tag) <a id="html-tag"></a> consists of an [open -tag](#open-tag), a [closing tag](#closing-tag), an [HTML -comment](#html-comment), a [processing -instruction](#processing-instruction), an [element type -declaration](#element-type-declaration), or a [CDATA -section](#cdata-section). - -Here are some simple open tags: - -. -<a><bab><c2c> -. -<p><a><bab><c2c></p> -. - -Empty elements: - -. -<a/><b2/> -. -<p><a/><b2/></p> -. - -Whitespace is allowed: - -. -<a /><b2 -data="foo" > -. -<p><a /><b2 -data="foo" ></p> -. - -With attributes: - -. -<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> -. - -Illegal tag names, not parsed as HTML: - -. -<33> <__> -. -<p><33> <__></p> -. - -Illegal attribute names: - -. -<a h*#ref="hi"> -. -<p><a h*#ref="hi"></p> -. - -Illegal attribute values: - -. -<a href="hi'> <a href=hi'> -. -<p><a href="hi'> <a href=hi'></p> -. - -Illegal whitespace: - -. -< a>< -foo><bar/ > -. -<p>< a>< -foo><bar/ ></p> -. - -Missing whitespace: - -. -<a href='bar'title=title> -. -<p><a href='bar'title=title></p> -. - -Closing tags: - -. -</a> -</foo > -. -<p></a> -</foo ></p> -. - -Illegal attributes in closing tag: - -. -</a href="foo"> -. -<p></a href="foo"></p> -. - -Comments: - -. -foo <!-- this is a -comment - with hyphen --> -. -<p>foo <!-- this is a -comment - with hyphen --></p> -. - -. -foo <!-- not a comment -- two hyphens --> -. -<p>foo <!-- not a comment -- two hyphens --></p> -. - -Processing instructions: - -. -foo <?php echo $a; ?> -. -<p>foo <?php echo $a; ?></p> -. - -Declarations: - -. -foo <!ELEMENT br EMPTY> -. -<p>foo <!ELEMENT br EMPTY></p> -. - -CDATA sections: - -. -foo <![CDATA[>&<]]> -. -<p>foo <![CDATA[>&<]]></p> -. - -Entities are preserved in HTML attributes: - -. -<a href="ö"> -. -<p><a href="ö"></p> -. - -Backslash escapes do not work in HTML attributes: - -. -<a href="\*"> -. -<p><a href="\*"></p> -. - -. -<a href="\""> -. -<p><a href="""></p> -. - -## Hard line breaks - -A line break (not in a code span or HTML tag) that is preceded -by two or more spaces is parsed as a linebreak (rendered -in HTML as a `<br />` tag): - -. -foo -baz -. -<p>foo<br /> -baz</p> -. - -For a more visible alternative, a backslash before the newline may be -used instead of two spaces: - -. -foo\ -baz -. -<p>foo<br /> -baz</p> -. - -More than two spaces can be used: - -. -foo -baz -. -<p>foo<br /> -baz</p> -. - -Leading spaces at the beginning of the next line are ignored: - -. -foo - bar -. -<p>foo<br /> -bar</p> -. - -. -foo\ - bar -. -<p>foo<br /> -bar</p> -. - -Line breaks can occur inside emphasis, links, and other constructs -that allow inline content: - -. -*foo -bar* -. -<p><em>foo<br /> -bar</em></p> -. - -. -*foo\ -bar* -. -<p><em>foo<br /> -bar</em></p> -. - -Line breaks do not occur inside code spans - -. -`code -span` -. -<p><code>code span</code></p> -. - -. -`code\ -span` -. -<p><code>code\ span</code></p> -. - -or HTML tags: - -. -<a href="foo -bar"> -. -<p><a href="foo -bar"></p> -. - -. -<a href="foo\ -bar"> -. -<p><a href="foo\ -bar"></p> -. - -## Soft line breaks - -A regular line break (not in a code span or HTML tag) that is not -preceded by two or more spaces is parsed as a softbreak. (A -softbreak may be rendered in HTML either as a newline or as a space. -The result will be the same in browsers. In the examples here, a -newline will be used.) - -. -foo -baz -. -<p>foo -baz</p> -. - -Spaces at the end of the line and beginning of the next line are -removed: - -. -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. - -## Strings - -Any characters not given an interpretation by the above rules will -be parsed as string content. - -. -hello $.;'there -. -<p>hello $.;'there</p> -. - -. -Foo χρῆν -. -<p>Foo χρῆν</p> -. - -Internal spaces are preserved verbatim: - -. -Multiple spaces -. -<p>Multiple spaces</p> -. - -<!-- END TESTS --> - -# Appendix A: A parsing strategy {-} - -## Overview {-} - -Parsing has two phases: - -1. In the first phase, lines of input are consumed and the block -structure of the document---its division into paragraphs, block quotes, -list items, and so on---is constructed. Text is assigned to these -blocks but not parsed. Link reference definitions are parsed and a -map of links is constructed. - -2. In the second phase, the raw text contents of paragraphs and headers -are parsed into sequences of Markdown inline elements (strings, -code spans, links, emphasis, and so on), using the map of link -references constructed in phase 1. - -## The document tree {-} - -At each point in processing, the document is represented as a tree of -**blocks**. The root of the tree is a `document` block. The `document` -may have any number of other blocks as **children**. These children -may, in turn, have other blocks as children. The last child of a block -is normally considered **open**, meaning that subsequent lines of input -can alter its contents. (Blocks that are not open are **closed**.) -Here, for example, is a possible document tree, with the open blocks -marked by arrows: - -``` tree --> document - -> block_quote - paragraph - "Lorem ipsum dolor\nsit amet." - -> list (type=bullet tight=true bullet_char=-) - list_item - paragraph - "Qui *quodsi iracundia*" - -> list_item - -> paragraph - "aliquando id" -``` - -## How source lines alter the document tree {-} - -Each line that is processed has an effect on this tree. The line is -analyzed and, depending on its contents, the document may be altered -in one or more of the following ways: - -1. One or more open blocks may be closed. -2. One or more new blocks may be created as children of the - last open block. -3. Text may be added to the last (deepest) open block remaining - on the tree. - -Once a line has been incorporated into the tree in this way, -it can be discarded, so input can be read in a stream. - -We can see how this works by considering how the tree above is -generated by four lines of Markdown: - -``` markdown -> Lorem ipsum dolor -sit amet. -> - Qui *quodsi iracundia* -> - aliquando id -``` - -At the outset, our document model is just - -``` tree --> document -``` - -The first line of our text, - -``` markdown -> Lorem ipsum dolor -``` - -causes a `block_quote` block to be created as a child of our -open `document` block, and a `paragraph` block as a child of -the `block_quote`. Then the text is added to the last open -block, the `paragraph`: - -``` tree --> document - -> block_quote - -> paragraph - "Lorem ipsum dolor" -``` - -The next line, - -``` markdown -sit amet. -``` - -is a "lazy continuation" of the open `paragraph`, so it gets added -to the paragraph's text: - -``` tree --> document - -> block_quote - -> paragraph - "Lorem ipsum dolor\nsit amet." -``` - -The third line, - -``` markdown -> - Qui *quodsi iracundia* -``` - -causes the `paragraph` block to be closed, and a new `list` block -opened as a child of the `block_quote`. A `list_item` is also -added as a child of the `list`, and a `paragraph` as a child of -the `list_item`. The text is then added to the new `paragraph`: - -``` tree --> document - -> block_quote - paragraph - "Lorem ipsum dolor\nsit amet." - -> list (type=bullet tight=true bullet_char=-) - -> list_item - -> paragraph - "Qui *quodsi iracundia*" -``` - -The fourth line, - -``` markdown -> - aliquando id -``` - -causes the `list_item` (and its child the `paragraph`) to be closed, -and a new `list_item` opened up as child of the `list`. A `paragraph` -is added as a child of the new `list_item`, to contain the text. -We thus obtain the final tree: - -``` tree --> document - -> block_quote - paragraph - "Lorem ipsum dolor\nsit amet." - -> list (type=bullet tight=true bullet_char=-) - list_item - paragraph - "Qui *quodsi iracundia*" - -> list_item - -> paragraph - "aliquando id" -``` - -## From block structure to the final document {-} - -Once all of the input has been parsed, all open blocks are closed. - -We then "walk the tree," visiting every node, and parse raw -string contents of paragraphs and headers as inlines. At this -point we have seen all the link reference definitions, so we can -resolve reference links as we go. - -``` tree -document - block_quote - paragraph - str "Lorem ipsum dolor" - softbreak - str "sit amet." - list (type=bullet tight=true bullet_char=-) - list_item - paragraph - str "Qui " - emph - str "quodsi iracundia" - list_item - paragraph - str "aliquando id" -``` - -Notice how the newline in the first paragraph has been parsed as -a `softbreak`, and the asterisks in the first list item have become -an `emph`. - -The document can be rendered as HTML, or in any other format, given -an appropriate renderer. - - |