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

bar

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

*foo*

. .

foo

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

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

``` c int x = 33; ``` . To start an [HTML block] with a tag that is *not* in the list of block-level tags in (6), you must put the tag by itself on the first line (and it must be complete): . *bar* . *bar* . In type 7 blocks, the [tag name] can be anything: . *bar* . *bar* . . *bar* . *bar* . . *bar* . *bar* . These rules are designed to allow us to work with tags that can function as either block-level or inline-level tags. The `` tag is a nice example. We can surround content with `` tags in three different ways. In this case, we get a raw HTML block, because the `` tag is on a line by itself: . ~~*foo*~~ . ~~*foo*~~ . In this case, we get a raw HTML block that just includes the `` tag (because it ends with the following blank line). So the contents get interpreted as CommonMark: . ~~*foo*~~ .
~~foo~~
. Finally, in this case, the `` tags are interpreted as [raw HTML] *inside* the CommonMark paragraph. (Because the tag is not on a line by itself, we get inline HTML rather than an [HTML block].) . ~~*foo*~~ .
~~foo~~
. HTML tags designed to contain literal content (`script`, `style`, `pre`), comments, processing instructions, and declarations are treated somewhat differently. Instead of ending at the first blank line, these blocks end at the first line containing a corresponding end tag. As a result, these blocks can contain blank lines: A pre tag (type 1): .
import Text.HTML.TagSoup main :: IO () main = print $ parseTags tags
.
import Text.HTML.TagSoup main :: IO () main = print $ parseTags tags
. A script tag (type 1): . . . A style tag (type 1): . . . If there is no matching end tag, the block will end at the end of the document (or the enclosing [block quote][block quotes] or [list item][list items]): . *foo* .
foo
. . *bar* *baz* . *bar*
baz
. Note that anything on the last line after the end tag will be included in the [HTML block]: . 1. *bar* . 1. *bar* . A comment (type 2): . . . A processing instruction (type 3): . '; ?> . '; ?> . A declaration (type 4): . . . CDATA (type 5): . . . The opening tag can be indented 1-3 spaces, but not 4: . .

. .

.

<div>
. An HTML block of types 1--6 can interrupt a paragraph, and need not be preceded by a blank line. . Foo
bar
.
Foo

bar
. However, a following blank line is needed, except at the end of a document, and except for blocks of types 1--5, above: .
bar
*foo* .
bar
*foo* . HTML blocks of type 7 cannot interrupt a paragraph: . Foo baz .
Foo baz
. This rule differs from John Gruber's original Markdown syntax specification, which says: > The only restrictions are that block-level HTML elements — > e.g. `
`, ``, `
`, `
`, etc. — must be separated from > surrounding content by blank lines, and the start and end tags of the > block should not be indented with tabs or spaces. In some ways Gruber's rule is more restrictive than the one given here: - It requires that an HTML block be preceded by a blank line. - It does not allow the start tag to be indented. - It requires a matching end tag, which it also does not allow to be indented. Most Markdown implementations (including some of Gruber's own) do not respect all of these restrictions. There is one respect, however, in which Gruber's rule is more liberal than the one given here, since it allows blank lines to occur inside an HTML block. There are two reasons for disallowing them here. First, it removes the need to parse balanced tags, which is expensive and can require backtracking from the end of the document if no matching end tag is found. Second, it provides a very simple and flexible way of including Markdown content inside HTML tags: simply separate the Markdown from the HTML using blank lines: Compare: .
*Emphasized* text.
.

Emphasized text.

. .
*Emphasized* text.
.
*Emphasized* text.
. Some Markdown implementations have adopted a convention of interpreting content inside tags as text if the open tag has the attribute `markdown=1`. The rule given above seems a simpler and more elegant way of achieving the same expressive power, which is also much simpler to parse. The main potential drawback is that one can no longer paste HTML blocks into Markdown documents with 100% reliability. However, *in most cases* this will work fine, because the blank lines in HTML are usually followed by HTML block tags. For example: .

Hi

.

Hi

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

Hi

.
<td> Hi </td>

. Fortunately, blank lines are usually not necessary and can be deleted. The exception is inside `
` tags, but as described above, raw HTML blocks starting with `
` *can* contain blank lines. ## Link reference definitions A [link reference definition](@link-reference-definition) consists of a [link label], indented up to three spaces, followed by a colon (`:`), optional [whitespace] (including up to one [line ending]), a [link destination], optional [whitespace] (including up to one [line ending]), and an optional [link title], which if it is present must be separated from the [link destination] by [whitespace]. No further [non-whitespace character]s may occur on the line. A [link reference definition] does not correspond to a structural element of a document. Instead, it defines a label which can be used in [reference link]s and reference-style [images] elsewhere in the document. [Link reference definitions] can come either before or after the links that use them. . [foo]: /url "title" [foo] .
foo
. . [foo]: /url 'the title' [foo] .
foo
. . [Foo*bar\]]:my_(url) 'title (with parens)' [Foo*bar\]] .
Foo*bar]
. . [Foo bar]: 'title' [Foo bar] .
Foo bar
. The title may extend over multiple lines: . [foo]: /url ' title line1 line2 ' [foo] .
foo
. However, it may not contain a [blank line]: . [foo]: /url 'title with blank line' [foo] .
[foo]: /url 'title

with blank line'

[foo]
. The title may be omitted: . [foo]: /url [foo] .
foo
. The link destination may not be omitted: . [foo]: [foo] .
[foo]:

[foo]
. Both title and destination can contain backslash escapes and literal backslashes: . [foo]: /url\bar\*baz "foo\"bar\baz" [foo] .
foo
. A link can come before its corresponding definition: . [foo] [foo]: url .
foo
. If there are several matching definitions, the first one takes precedence: . [foo] [foo]: first [foo]: second .
foo
. As noted in the section on [Links], matching of labels is case-insensitive (see [matches]). . [FOO]: /url [Foo] .
Foo
. . [ΑΓΩ]: /φου [αγω] .
αγω
. Here is a link reference definition with no corresponding link. It contributes nothing to the document. . [foo]: /url . . Here is another one: . [ foo ]: /url bar .
bar
. This is not a link reference definition, because there are [non-whitespace character]s after the title: . [foo]: /url "title" ok .
[foo]: /url "title" ok
. This is a link reference definition, but it has no title: . [foo]: /url "title" ok .
"title" ok
. This is not a link reference definition, because it is indented four spaces: . [foo]: /url "title" [foo] .
[foo]: /url "title"

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

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

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

bar

. Several [link reference definition]s can occur one after another, without intervening blank lines. . [foo]: /foo-url "foo" [bar]: /bar-url "bar" [baz]: /baz-url [foo], [bar], [baz] .
foo, bar, baz
. [Link reference definition]s can occur inside block containers, like lists and block quotations. They affect the entire document, not just the container in which they are defined: . [foo] > [foo]: /url .
foo

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

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

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

bbb
. Leading spaces are skipped: . aaa bbb .
aaa bbb
. Lines after the first may be indented any amount, since indented code blocks cannot interrupt paragraphs. . aaa bbb ccc .
aaa bbb ccc
. However, the first line may be indented at most three spaces, or an indented code block will be triggered: . aaa bbb .
aaa bbb
. . aaa bbb .
aaa

bbb
. Final spaces are stripped before inline parsing, so a paragraph that ends with two or more spaces will not end with a [hard line break]: . aaa bbb .
aaa
bbb
. ## Blank lines [Blank line]s between block-level elements are ignored, except for the role they play in determining whether a [list] is [tight] or [loose]. Blank lines at the beginning and end of the document are also ignored. . aaa # aaa .
aaa

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

Foo

bar baz

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

Foo

bar baz

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

Foo

bar baz

. Four spaces gives us a code block: . > # Foo > bar > baz .
> # Foo > bar > baz
. The Laziness clause allows us to omit the `>` before a paragraph continuation line: . > # Foo > bar baz .

Foo

bar baz

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

bar baz foo

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

foo

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

foo

bar

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

foo

bar
. . > ``` foo ``` .

foo

. Note that in the following case, we have a paragraph continuation line: . > foo - bar .

foo - bar

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

. . > > > .

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

foo

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

foo

bar

. (Most current Markdown implementations, including John Gruber's original `Markdown.pl`, will parse this example as a single block quote with two paragraphs. But it seems better to allow the author to decide whether two block quotes or one are wanted.) Consecutiveness means that if we put these block quotes together, we get a single block quote: . > foo > bar .

foo bar

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

foo

bar

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

bar

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

aaa

bbb

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

bar baz

. . > bar baz .

bar

baz
. . > bar > baz .

bar

baz
. It is a consequence of the Laziness rule that any number of initial `>`s may be omitted on a continuation line of a nested block quote: . > > > foo bar .

foo bar

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

foo bar baz

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

code

not code

. ## List items A [list marker](@list-marker) is a [bullet list marker] or an [ordered list marker]. A [bullet list marker](@bullet-list-marker) is a `-`, `+`, or `*` character. An [ordered list marker](@ordered-list-marker) is a sequence of 1--9 arabic digits (`0-9`), followed by either a `.` character or a `)` character. (The reason for the length limit is that with 10 digits we start seeing integer overflows in some browsers.) The following rules define [list items]: 1. **Basic case.** If a sequence of lines *Ls* constitute a sequence of blocks *Bs* starting with a [non-whitespace character] and not separated from each other by more than one blank line, and *M* is a list marker of width *W* followed by 0 < *N* < 5 spaces, then the result of prepending *M* and the following spaces to the first line of *Ls*, and indenting subsequent lines of *Ls* by *W + N* spaces, is a list item with *Bs* as its contents. The type of the list item (bullet or ordered) is determined by the type of its list marker. If the list item is ordered, then it is also assigned a start number, based on the ordered list marker. For example, let *Ls* be the lines . A paragraph with two lines. indented code > A block quote. .
A paragraph with two lines.

indented code

A block quote.

. And let *M* be the marker `1.`, and *N* = 2. Then rule #1 says that the following is an ordered list item with start number 1, and the same contents as *Ls*: . 1. A paragraph with two lines. indented code > A block quote. .

A paragraph with two lines.

indented code

A block quote.

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

one

two
. . - one two .

one

two

. . - one two .

one

two
. . - one two .

one

two

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

one

two

. Here `two` occurs in the same column as the list marker `1.`, but is actually contained in the list item, because there is sufficient indentation after the last containing blockquote marker. The converse is also possible. In the following example, the word `two` occurs far to the right of the initial text of the list item, `one`, but it is not considered part of the list item, because it is not indented far enough past the blockquote marker: . >>- one >> > > two .

one

two

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

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

foo

bar

foo

bar

foo bar

baz

foo bar

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

foo

bar

baz

bam

. A list item that contains an indented code block will preserve empty lines within the code block verbatim, unless there are two or more empty lines in a row (since as described above, two blank lines end the list): . - Foo bar baz .

Foo

bar baz

. . - Foo bar baz .

Foo

bar

baz
. Note that ordered list start numbers must be nine digits or less: . 123456789. ok .

ok

. . 1234567890. not ok .
1234567890. not ok
. A start number may begin with 0s: . 0. ok .

ok

. . 003. ok .

ok

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

foo

bar

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

foo

bar

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

paragraph

more code
. . 1. indented code paragraph more code .

indented code

paragraph

more code

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

indented code

paragraph

more code

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

bar
. . - foo bar .

foo

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

foo

bar

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

foo

bar

baz

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

foo
. Here is an empty bullet list item: . - foo - - bar .

foo

bar

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

foo

bar

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

foo

bar

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

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

A paragraph with two lines.

indented code

A block quote.

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

A paragraph with two lines.

indented code

A block quote.

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

A paragraph with two lines.

indented code

A block quote.

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

A paragraph with two lines.

indented code

A block quote.

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

A paragraph with two lines.

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

Blockquote continued here.

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

Blockquote continued here.

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

foo

bar

baz

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

foo

bar

baz

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

foo

bar

. Three is not enough: . 10) foo - bar .

foo

bar

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

foo

. . 1. - 2. foo .

foo

. A list item can contain a heading: . - # Foo - Bar --- baz .

Foo

Bar
baz

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

foo

bar

baz

``` as the four-space rule demands, rather than a single list, ``` html

foo

bar

baz

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

one

two

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

one

two

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

foo

bar

baz

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

foo

bar

baz

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

bar

baz

. `Markdown.pl` does not allow this, through fear of triggering a list via a numeral in a hard-wrapped line: . The number of windows in my house is 14. The number of doors is 6. .
The number of windows in my house is

The number of doors is 6.

. Oddly, `Markdown.pl` *does* allow a blockquote to interrupt a paragraph, even though the same considerations might apply. We think that the two cases should be treated the same. Here are two reasons for allowing lists to interrupt paragraphs: First, it is natural and not uncommon for people to start lists without blank lines: I need to buy - new shoes - a coat - a plane ticket Second, we are attracted to a > [principle of uniformity](@principle-of-uniformity): > if a chunk of text has a certain > meaning, it will continue to have the same meaning when put into a > container block (such as a list item or blockquote). (Indeed, the spec for [list items] and [block quotes] presupposes this principle.) This principle implies that if * I need to buy - new shoes - a coat - a plane ticket is a list item containing a paragraph followed by a nested sublist, as all Markdown implementations agree it is (though the paragraph may be rendered without `
` tags, since the list is "tight"), then I need to buy - new shoes - a coat - a plane ticket by itself should be a paragraph followed by a nested sublist. Our adherence to the [principle of uniformity] thus inclines us to think that there are two coherent packages: 1. Require blank lines before *all* lists and blockquotes, including lists that occur as sublists inside other list items. 2. Require blank lines in none of these places. [reStructuredText](http://docutils.sourceforge.net/rst.html) takes the first approach, for which there is much to be said. But the second seems more consistent with established practice with Markdown. There can be blank lines between items, but two blank lines end a list: . - foo - bar - baz .

foo

bar

baz

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

foo

bar

baz

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

foo

bar

baz

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

foo

bar

baz

bim

. . - foo notcode - foo code .

foo

notcode

foo

code
. List items need not be indented to the same level. The following list items will be treated as items at the same list level, since none is indented enough to belong to the previous list item: . - a - b - c - d - e - f - g - h - i .

a

b

c

d

e

f

g

h

i

. . 1. a 2. b 3. c .

a

b

c

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

a

b

c

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

a

c

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

a

b

c

d

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

a

b

d

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

a

b

c

. This is a tight list, because the blank line is between two paragraphs of a sublist. So the sublist is loose while the outer list is tight: . - a - b c - d .

a

b

c

d

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

a

b

c

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

a

b

c

d

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

a

. . - a - b .

a

b

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

foo

bar

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

foo

bar

baz

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

a

b

c

d

e

f

. # Inlines Inlines are parsed sequentially from the beginning of the character stream to the end (left to right, in left-to-right languages). Thus, for example, in . `hi`lo` .
hilo`
. `hi` is parsed as code, leaving the backtick at the end as a literal backtick. ## Backslash escapes Any ASCII punctuation character may be backslash-escaped: . \!\"\#\$\%\&\'\*\+\,\-\.\/\:\;\<\=\>\?\@\[\\\]\^\_\`\{\|\}\~ .
!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
. Backslashes before other characters are treated as literal backslashes: . \→\A\a\ \3\φ\« .
\→\A\a\ \3\φ\«
. Escaped characters are treated as regular characters and do not have their usual Markdown meanings: . \*not emphasized* \
not a tag \[not a link](/foo) \`not code` 1\. not a list \* not a list \# not a heading \[foo]: /url "not a reference" .
*not emphasized* <br/> not a tag [not a link](/foo) `not code` 1. not a list * not a list # not a heading [foo]: /url "not a reference"
. If a backslash is itself escaped, the following character is not: . \\*emphasis* .
\emphasis
. A backslash at the end of the line is a [hard line break]: . foo\ bar .
foo
bar
. Backslash escapes do not work in code blocks, code spans, autolinks, or raw HTML: . `` \[\` `` .
\[\`
. . \[\] .
\[\]
. . ~~~ \[\] ~~~ .
\[\]
. . .
http://example.com?find=\*
. . . . But they work in all other contexts, including URLs and link titles, link references, and [info string]s in [fenced code block]s: . [foo](/bar\* "ti\*tle") .
foo
. . [foo] [foo]: /bar\* "ti\*tle" .
foo
. . ``` foo\+bar foo ``` .
foo
. ## Entity and numeric character references All valid HTML entity references and numeric character references, except those occuring in code blocks and code spans, are recognized as such and treated as equivalent to the corresponding Unicode characters. Conforming CommonMark parsers need not store information about whether a particular character was represented in the source using a Unicode character or an entity reference. [Entity references](@entity-references) consist of `&` + any of the valid HTML5 entity names + `;`. The document is used as an authoritative source for the valid entity references and their corresponding code points. . & © Æ Ď ¾ ℋ ⅆ ∲ ≧̸ .
& © Æ Ď ¾ ℋ ⅆ ∲ ≧̸
. [Decimal numeric character references](@decimal-numeric-character-references) consist of `&#` + a string of 1--8 arabic digits + `;`. A numeric character reference is parsed as the corresponding Unicode character. Invalid Unicode code points will be replaced by the REPLACEMENT CHARACTER (`U+FFFD`). For security reasons, the code point `U+0000` will also be replaced by `U+FFFD`. . # Ӓ Ϡ � � .
# Ӓ Ϡ � �
. [Hexadecimal numeric character references](@hexadecimal-numeric-character-references) consist of `&#` + either `X` or `x` + a string of 1-8 hexadecimal digits + `;`. They too are parsed as the corresponding Unicode character (this time specified with a hexadecimal numeral instead of decimal). . " ആ ಫ .
" ആ ಫ
. Here are some nonentities: . &x; &#; &#x; &ThisIsNotDefined; &hi?; .
&nbsp &x; &#; &#x; &ThisIsNotDefined; &hi?;
. Although HTML5 does accept some entity references without a trailing semicolon (such as `©`), these are not recognized here, because it makes the grammar too ambiguous: . © .
&copy
. Strings that are not on the list of HTML5 named entities are not recognized as entity references either: . &MadeUpEntity; .
&MadeUpEntity;
. Entity and numeric character references are recognized in any context besides code spans or code blocks, including URLs, [link title]s, and [fenced code block][] [info string]s: . . . . [foo](/föö "föö") .
foo
. . [foo] [foo]: /föö "föö" .
foo
. . ``` föö foo ``` .
foo
. Entity and numeric character references are treated as literal text in code spans and code blocks: . `föö` .
föö
. . föfö .
föfö
. ## Code spans A [backtick string](@backtick-string) is a string of one or more backtick characters (`` ` ``) that is neither preceded nor followed by a backtick. A [code span](@code-span) begins with a backtick string and ends with a backtick string of equal length. The contents of the code span are the characters between the two backtick strings, with leading and trailing spaces and [line ending]s removed, and [whitespace] collapsed to single spaces. This is a simple code span: . `foo` .
foo
. Here two backticks are used, because the code contains a backtick. This example also illustrates stripping of leading and trailing spaces: . `` foo ` bar `` .
foo ` bar
. This example shows the motivation for stripping leading and trailing spaces: . ` `` ` .
``
. [Line ending]s are treated like spaces: . `` foo `` .
foo
. Interior spaces and [line ending]s are collapsed into single spaces, just as they would be by a browser: . `foo bar baz` .
foo bar baz
. Q: Why not just leave the spaces, since browsers will collapse them anyway? A: Because we might be targeting a non-HTML format, and we shouldn't rely on HTML-specific rendering assumptions. (Existing implementations differ in their treatment of internal spaces and [line ending]s. Some, including `Markdown.pl` and `showdown`, convert an internal [line ending] into a `
` tag. But this makes things difficult for those who like to hard-wrap their paragraphs, since a line break in the midst of a code span will cause an unintended line break in the output. Others just leave internal spaces as they are, which is fine if only HTML is being targeted.) . `foo `` bar` .
foo `` bar
. Note that backslash escapes do not work in code spans. All backslashes are treated literally: . `foo\`bar` .
foo\bar`
. Backslash escapes are never needed, because one can always choose a string of *n* backtick characters as delimiters, where the code does not contain any strings of exactly *n* backtick characters. Code span backticks have higher precedence than any other inline constructs except HTML tags and autolinks. Thus, for example, this is not parsed as emphasized text, since the second `*` is part of a code span: . *foo`*` .
*foo*
. And this is not parsed as a link: . [not a `link](/foo`) .
[not a link](/foo)
. Code spans, HTML tags, and autolinks have the same precedence. Thus, this is code: . `` .
<a href="">`
. But this is an HTML tag: . ` .
`
. And this is code: . `` .
<http://foo.bar.baz>`
. But this is an autolink: . ` .
http://foo.bar.`baz`
. When a backtick string is not closed by a matching backtick string, we just have literal backticks: . ```foo`` .
```foo``
. . `foo .
`foo
. ## Emphasis and strong emphasis John Gruber's original [Markdown syntax description](http://daringfireball.net/projects/markdown/syntax#em) says: > Markdown treats asterisks (`*`) and underscores (`_`) as indicators of > emphasis. Text wrapped with one `*` or `_` will be wrapped with an HTML > `` tag; double `*`'s or `_`'s will be wrapped with an HTML `` > tag. This is enough for most users, but these rules leave much undecided, especially when it comes to nested emphasis. The original `Markdown.pl` test suite makes it clear that triple `***` and `___` delimiters can be used for strong emphasis, and most implementations have also allowed the following patterns: ``` markdown ***strong emph*** ***strong** in emph* ***emph* in strong** **in strong *emph*** *in emph **strong*** ``` The following patterns are less widely supported, but the intent is clear and they are useful (especially in contexts like bibliography entries): ``` markdown *emph *with emph* in it* **strong **with strong** in it** ``` Many implementations have also restricted intraword emphasis to the `*` forms, to avoid unwanted emphasis in words containing internal underscores. (It is best practice to put these in code spans, but users often do not.) ``` markdown internal emphasis: foo*bar*baz no emphasis: foo_bar_baz ``` The rules given below capture all of these patterns, while allowing for efficient parsing strategies that do not backtrack. First, some definitions. A [delimiter run](@delimiter-run) is either a sequence of one or more `*` characters that is not preceded or followed by a `*` character, or a sequence of one or more `_` characters that is not preceded or followed by a `_` character. A [left-flanking delimiter run](@left-flanking-delimiter-run) is a [delimiter run] that is (a) not followed by [Unicode whitespace], and (b) either not followed by a [punctuation character], or preceded by [Unicode whitespace] or a [punctuation character]. For purposes of this definition, the beginning and the end of the line count as Unicode whitespace. A [right-flanking delimiter run](@right-flanking-delimiter-run) is a [delimiter run] that is (a) not preceded by [Unicode whitespace], and (b) either not preceded by a [punctuation character], or followed by [Unicode whitespace] or a [punctuation character]. For purposes of this definition, the beginning and the end of the line count as Unicode whitespace. Here are some examples of delimiter runs. - left-flanking but not right-flanking: ``` ***abc _abc **"abc" _"abc" ``` - right-flanking but not left-flanking: ``` abc*** abc_ "abc"** "abc"_ ``` - Both left and right-flanking: ``` abc***def "abc"_"def" ``` - Neither left nor right-flanking: ``` abc *** def a _ b ``` (The idea of distinguishing left-flanking and right-flanking delimiter runs based on the character before and the character after comes from Roopesh Chander's [vfmd](http://www.vfmd.org/vfmd-spec/specification/#procedure-for-identifying-emphasis-tags). vfmd uses the terminology "emphasis indicator string" instead of "delimiter run," and its rules for distinguishing left- and right-flanking runs are a bit more complex than the ones given here.) The following rules define emphasis and strong emphasis: 1. A single `*` character [can open emphasis](@can-open-emphasis) iff (if and only if) it is part of a [left-flanking delimiter run]. 2. A single `_` character [can open emphasis] iff it is part of a [left-flanking delimiter run] and either (a) not part of a [right-flanking delimiter run] or (b) part of a [right-flanking delimiter run] preceded by punctuation. 3. A single `*` character [can close emphasis](@can-close-emphasis) iff it is part of a [right-flanking delimiter run]. 4. A single `_` character [can close emphasis] iff it is part of a [right-flanking delimiter run] and either (a) not part of a [left-flanking delimiter run] or (b) part of a [left-flanking delimiter run] followed by punctuation. 5. A double `**` [can open strong emphasis](@can-open-strong-emphasis) iff it is part of a [left-flanking delimiter run]. 6. A double `__` [can open strong emphasis] iff it is part of a [left-flanking delimiter run] and either (a) not part of a [right-flanking delimiter run] or (b) part of a [right-flanking delimiter run] preceded by punctuation. 7. A double `**` [can close strong emphasis](@can-close-strong-emphasis) iff it is part of a [right-flanking delimiter run]. 8. A double `__` [can close strong emphasis] it is part of a [right-flanking delimiter run] and either (a) not part of a [left-flanking delimiter run] or (b) part of a [left-flanking delimiter run] followed by punctuation. 9. Emphasis begins with a delimiter that [can open emphasis] and ends with a delimiter that [can close emphasis], and that uses the same character (`_` or `*`) as the opening delimiter. There must be a nonempty sequence of inlines between the open delimiter and the closing delimiter; these form the contents of the emphasis inline. 10. Strong emphasis begins with a delimiter that [can open strong emphasis] and ends with a delimiter that [can close strong emphasis], and that uses the same character (`_` or `*`) as the opening delimiter. There must be a nonempty sequence of inlines between the open delimiter and the closing delimiter; these form the contents of the strong emphasis inline. 11. A literal `*` character cannot occur at the beginning or end of `*`-delimited emphasis or `**`-delimited strong emphasis, unless it is backslash-escaped. 12. A literal `_` character cannot occur at the beginning or end of `_`-delimited emphasis or `__`-delimited strong emphasis, unless it is backslash-escaped. Where rules 1--12 above are compatible with multiple parsings, the following principles resolve ambiguity: 13. The number of nestings should be minimized. Thus, for example, an interpretation `...` is always preferred to `...`. 14. An interpretation `...` is always preferred to `..`. 15. When two potential emphasis or strong emphasis spans overlap, so that the second begins before the first ends and ends after the first ends, the first takes precedence. Thus, for example, `*foo _bar* baz_` is parsed as `foo _bar baz_` rather than `*foo bar* baz`. For the same reason, `**foo*bar**` is parsed as `foobar*` rather than `foo*bar`. 16. When there are two potential emphasis or strong emphasis spans with the same closing delimiter, the shorter one (the one that opens later) takes precedence. Thus, for example, `**foo **bar baz**` is parsed as `**foo bar baz` rather than `foo **bar baz`. 17. Inline code spans, links, images, and HTML tags group more tightly than emphasis. So, when there is a choice between an interpretation that contains one of these elements and one that does not, the former always wins. Thus, for example, `*[foo*](bar)` is parsed as `*foo*` rather than as `[foo](bar)`. These rules can be illustrated through a series of examples. Rule 1: . *foo bar* .
foo bar
. This is not emphasis, because the opening `*` is followed by whitespace, and hence not part of a [left-flanking delimiter run]: . a * foo bar* .
a * foo bar*
. This is not emphasis, because the opening `*` is preceded by an alphanumeric and followed by punctuation, and hence not part of a [left-flanking delimiter run]: . a*"foo"* .
a*"foo"*
. Unicode nonbreaking spaces count as whitespace, too: . * a * .
* a *
. Intraword emphasis with `*` is permitted: . foo*bar* .
foobar
. . 5*6*78 .
5678
. Rule 2: . _foo bar_ .
foo bar
. This is not emphasis, because the opening `_` is followed by whitespace: . _ foo bar_ .
_ foo bar_
. This is not emphasis, because the opening `_` is preceded by an alphanumeric and followed by punctuation: . a_"foo"_ .
a_"foo"_
. Emphasis with `_` is not allowed inside words: . foo_bar_ .
foo_bar_
. . 5_6_78 .
5_6_78
. . пристаням_стремятся_ .
пристаням_стремятся_
. Here `_` does not generate emphasis, because the first delimiter run is right-flanking and the second left-flanking: . aa_"bb"_cc .
aa_"bb"_cc
. This is emphasis, even though the opening delimiter is both left- and right-flanking, because it is preceded by punctuation: . foo-_(bar)_ .
foo-(bar)
. Rule 3: This is not emphasis, because the closing delimiter does not match the opening delimiter: . _foo* .
_foo*
. This is not emphasis, because the closing `*` is preceded by whitespace: . *foo bar * .
*foo bar *
. A newline also counts as whitespace: . *foo bar * .
*foo bar

. This is not emphasis, because the second `*` is preceded by punctuation and followed by an alphanumeric (hence it is not part of a [right-flanking delimiter run]: . *(*foo) .
*(*foo)
. The point of this restriction is more easily appreciated with this example: . *(*foo*)* .
(foo)
. Intraword emphasis with `*` is allowed: . *foo*bar .
foobar
. Rule 4: This is not emphasis, because the closing `_` is preceded by whitespace: . _foo bar _ .
_foo bar _
. This is not emphasis, because the second `_` is preceded by punctuation and followed by an alphanumeric: . _(_foo) .
_(_foo)
. This is emphasis within emphasis: . _(_foo_)_ .
(foo)
. Intraword emphasis is disallowed for `_`: . _foo_bar .
_foo_bar
. . _пристаням_стремятся .
_пристаням_стремятся
. . _foo_bar_baz_ .
foo_bar_baz
. This is emphasis, even though the closing delimiter is both left- and right-flanking, because it is followed by punctuation: . _(bar)_. .
(bar).
. Rule 5: . **foo bar** .
foo bar
. This is not strong emphasis, because the opening delimiter is followed by whitespace: . ** foo bar** .
** foo bar**
. This is not strong emphasis, because the opening `**` is preceded by an alphanumeric and followed by punctuation, and hence not part of a [left-flanking delimiter run]: . a**"foo"** .
a**"foo"**
. Intraword strong emphasis with `**` is permitted: . foo**bar** .
foobar
. Rule 6: . __foo bar__ .
foo bar
. This is not strong emphasis, because the opening delimiter is followed by whitespace: . __ foo bar__ .
__ foo bar__
. A newline counts as whitespace: . __ foo bar__ .
__ foo bar__
. This is not strong emphasis, because the opening `__` is preceded by an alphanumeric and followed by punctuation: . a__"foo"__ .
a__"foo"__
. Intraword strong emphasis is forbidden with `__`: . foo__bar__ .
foo__bar__
. . 5__6__78 .
5__6__78
. . пристаням__стремятся__ .
пристаням__стремятся__
. . __foo, __bar__, baz__ .
foo, bar, baz
. This is strong emphasis, even though the opening delimiter is both left- and right-flanking, because it is preceded by punctuation: . foo-__(bar)__ .
foo-(bar)
. Rule 7: This is not strong emphasis, because the closing delimiter is preceded by whitespace: . **foo bar ** .
**foo bar **
. (Nor can it be interpreted as an emphasized `*foo bar *`, because of Rule 11.) This is not strong emphasis, because the second `**` is preceded by punctuation and followed by an alphanumeric: . **(**foo) .
**(**foo)
. The point of this restriction is more easily appreciated with these examples: . *(**foo**)* .
(foo)
. . **Gomphocarpus (*Gomphocarpus physocarpus*, syn. *Asclepias physocarpa*)** .
Gomphocarpus (Gomphocarpus physocarpus, syn. Asclepias physocarpa)
. . **foo "*bar*" foo** .
foo "bar" foo
. Intraword emphasis: . **foo**bar .
foobar
. Rule 8: This is not strong emphasis, because the closing delimiter is preceded by whitespace: . __foo bar __ .
__foo bar __
. This is not strong emphasis, because the second `__` is preceded by punctuation and followed by an alphanumeric: . __(__foo) .
__(__foo)
. The point of this restriction is more easily appreciated with this example: . _(__foo__)_ .
(foo)
. Intraword strong emphasis is forbidden with `__`: . __foo__bar .
__foo__bar
. . __пристаням__стремятся .
__пристаням__стремятся
. . __foo__bar__baz__ .
foo__bar__baz
. This is strong emphasis, even though the closing delimiter is both left- and right-flanking, because it is followed by punctuation: . __(bar)__. .
(bar).
. Rule 9: Any nonempty sequence of inline elements can be the contents of an emphasized span. . *foo [bar](/url)* .
foo bar
. . *foo bar* .
foo bar
. In particular, emphasis and strong emphasis can be nested inside emphasis: . _foo __bar__ baz_ .
foo bar baz
. . _foo _bar_ baz_ .
foo bar baz
. . __foo_ bar_ .
foo bar
. . *foo *bar** .
foo bar
. . *foo **bar** baz* .
foo bar baz
. But note: . *foo**bar**baz* .
foobarbaz
. The difference is that in the preceding case, the internal delimiters [can close emphasis], while in the cases with spaces, they cannot. . ***foo** bar* .
foo bar
. . *foo **bar*** .
foo bar
. Note, however, that in the following case we get no strong emphasis, because the opening delimiter is closed by the first `*` before `bar`: . *foo**bar*** .
foobar**
. Indefinite levels of nesting are possible: . *foo **bar *baz* bim** bop* .
foo bar baz bim bop
. . *foo [*bar*](/url)* .
foo bar
. There can be no empty emphasis or strong emphasis: . ** is not an empty emphasis .
** is not an empty emphasis
. . **** is not an empty strong emphasis .
**** is not an empty strong emphasis
. Rule 10: Any nonempty sequence of inline elements can be the contents of an strongly emphasized span. . **foo [bar](/url)** .
foo bar
. . **foo bar** .
foo bar
. In particular, emphasis and strong emphasis can be nested inside strong emphasis: . __foo _bar_ baz__ .
foo bar baz
. . __foo __bar__ baz__ .
foo bar baz
. . ____foo__ bar__ .
foo bar
. . **foo **bar**** .
foo bar
. . **foo *bar* baz** .
foo bar baz
. But note: . **foo*bar*baz** .
foobarbaz**
. The difference is that in the preceding case, the internal delimiters [can close emphasis], while in the cases with spaces, they cannot. . ***foo* bar** .
foo bar
. . **foo *bar*** .
foo bar
. Indefinite levels of nesting are possible: . **foo *bar **baz** bim* bop** .
foo bar baz bim bop
. . **foo [*bar*](/url)** .
foo bar
. There can be no empty emphasis or strong emphasis: . __ is not an empty emphasis .
__ is not an empty emphasis
. . ____ is not an empty strong emphasis .
____ is not an empty strong emphasis
. Rule 11: . foo *** .
foo ***
. . foo *\** .
foo *
. . foo *_* .
foo _
. . foo ***** .
foo *****
. . foo **\*** .
foo *
. . foo **_** .
foo _
. Note that when delimiters do not match evenly, Rule 11 determines that the excess literal `*` characters will appear outside of the emphasis, rather than inside it: . **foo* .
*foo
. . *foo** .
foo*
. . ***foo** .
*foo
. . ****foo* .
***foo
. . **foo*** .
foo*
. . *foo**** .
foo***
. Rule 12: . foo ___ .
foo ___
. . foo _\__ .
foo _
. . foo _*_ .
foo *
. . foo _____ .
foo _____
. . foo __\___ .
foo _
. . foo __*__ .
foo *
. . __foo_ .
_foo
. Note that when delimiters do not match evenly, Rule 12 determines that the excess literal `_` characters will appear outside of the emphasis, rather than inside it: . _foo__ .
foo_
. . ___foo__ .
_foo
. . ____foo_ .
___foo
. . __foo___ .
foo_
. . _foo____ .
foo___
. Rule 13 implies that if you want emphasis nested directly inside emphasis, you must use different delimiters: . **foo** .
foo
. . *_foo_* .
foo
. . __foo__ .
foo
. . _*foo*_ .
foo
. However, strong emphasis within strong emphasis is possible without switching delimiters: . ****foo**** .
foo
. . ____foo____ .
foo
. Rule 13 can be applied to arbitrarily long sequences of delimiters: . ******foo****** .
foo
. Rule 14: . ***foo*** .
foo
. . _____foo_____ .
foo
. Rule 15: . *foo _bar* baz_ .
foo _bar baz_
. . **foo*bar** .
foobar*
. . *foo __bar *baz bim__ bam* .
foo bar *baz bim bam
. Rule 16: . **foo **bar baz** .
**foo bar baz
. . *foo *bar baz* .
*foo bar baz
. Rule 17: . *[bar*](/url) .
*bar*
. . _foo [bar_](/url) .
_foo bar_
. . * .
*
. . ** .
**
. . __ .
__
. . *a `*`* .
a *
. . _a `_`_ .
a _
. . **a .
**a http://foo.bar/?q=**
. . __a .
__ahttp://foo.bar/?q=__
. ## Links A link contains [link text] (the visible text), a [link destination] (the URI that is the link destination), and optionally a [link title]. There are two basic kinds of links in Markdown. In [inline link]s the destination and title are given immediately after the link text. In [reference link]s the destination and title are defined elsewhere in the document. A [link text](@link-text) consists of a sequence of zero or more inline elements enclosed by square brackets (`[` and `]`). The following rules apply: - Links may not contain other links, at any level of nesting. If multiple otherwise valid link definitions appear nested inside each other, the inner-most definition is used. - Brackets are allowed in the [link text] only if (a) they are backslash-escaped or (b) they appear as a matched pair of brackets, with an open bracket `[`, a sequence of zero or more inlines, and a close bracket `]`. - Backtick [code span]s, [autolink]s, and raw [HTML tag]s bind more tightly than the brackets in link text. Thus, for example, `` [foo`]` `` could not be a link text, since the second `]` is part of a code span. - The brackets in link text bind more tightly than markers for [emphasis and strong emphasis]. Thus, for example, `*[foo*](url)` is a link. A [link destination](@link-destination) consists of either - a sequence of zero or more characters between an opening `<` and a closing `>` that contains no spaces, line breaks, or unescaped `<` or `>` characters, or - a nonempty sequence of characters that does not include ASCII space or control characters, and includes parentheses only if (a) they are backslash-escaped or (b) they are part of a balanced pair of unescaped parentheses that is not itself inside a balanced pair of unescaped parentheses. A [link title](@link-title) consists of either - a sequence of zero or more characters between straight double-quote characters (`"`), including a `"` character only if it is backslash-escaped, or - a sequence of zero or more characters between straight single-quote characters (`'`), including a `'` character only if it is backslash-escaped, or - a sequence of zero or more characters between matching parentheses (`(...)`), including a `)` character only if it is backslash-escaped. Although [link title]s may span multiple lines, they may not contain a [blank line]. An [inline link](@inline-link) consists of a [link text] followed immediately by a left parenthesis `(`, optional [whitespace], an optional [link destination], an optional [link title] separated from the link destination by [whitespace], optional [whitespace], and a right parenthesis `)`. The link's text consists of the inlines contained in the [link text] (excluding the enclosing square brackets). The link's URI consists of the link destination, excluding enclosing `<...>` if present, with backslash-escapes in effect as described above. The link's title consists of the link title, excluding its enclosing delimiters, with backslash-escapes in effect as described above. Here is a simple inline link: . [link](/uri "title") .
link
. The title may be omitted: . [link](/uri) .
link
. Both the title and the destination may be omitted: . [link]() .
link
. . [link](<>) .
link
. The destination cannot contain spaces or line breaks, even if enclosed in pointy brackets: . [link](/my uri) .
[link](/my uri)
. . [link]() .
[link](</my uri>)
. . [link](foo bar) .
[link](foo bar)
. . [link]() .
[link]()
. One level of balanced parentheses is allowed without escaping: . [link]((foo)and(bar)) .
link
. However, if you have parentheses within parentheses, you need to escape or use the `<...>` form: . [link](foo(and(bar))) .
[link](foo(and(bar)))
. . [link](foo(and$bar$)) .
link
. . [link]() .
link
. Parentheses and other symbols can also be escaped, as usual in Markdown: . [link](foo\)\:) .
link
. A link can contain fragment identifiers and queries: . [link](#fragment) [link](http://example.com#fragment) [link](http://example.com?foo=3#frag) .
link

link

link
. Note that a backslash before a non-escapable character is just a backslash: . [link](foo\bar) .
link
. URL-escaping should be left alone inside the destination, as all URL-escaped characters are also valid URL characters. Entity and numerical character references in the destination will be parsed into the corresponding Unicode code points, as usual. These may be optionally URL-escaped when written as HTML, but this spec does not enforce any particular policy for rendering URLs in HTML or other formats. Renderers may make different decisions about how to escape or normalize URLs in the output. . [link](foo%20bä) .
link
. Note that, because titles can often be parsed as destinations, if you try to omit the destination and keep the title, you'll get unexpected results: . [link]("title") .
link
. Titles may be in single quotes, double quotes, or parentheses: . [link](/url "title") [link](/url 'title') [link](/url (title)) .
link link link
. Backslash escapes and entity and numeric character references may be used in titles: . [link](/url "title \""") .
link
. Nested balanced quotes are not allowed without escaping: . [link](/url "title "and" title") .
[link](/url "title "and" title")
. But it is easy to work around this by using a different quote type: . [link](/url 'title "and" title') .
link
. (Note: `Markdown.pl` did allow double quotes inside a double-quoted title, and its test suite included a test demonstrating this. But it is hard to see a good rationale for the extra complexity this brings, since there are already many ways---backslash escaping, entity and numeric character references, or using a different quote type for the enclosing title---to write titles containing double quotes. `Markdown.pl`'s handling of titles has a number of other strange features. For example, it allows single-quoted titles in inline links, but not reference links. And, in reference links but not inline links, it allows a title to begin with `"` and end with `)`. `Markdown.pl` 1.0.1 even allows titles with no closing quotation mark, though 1.0.2b8 does not. It seems preferable to adopt a simple, rational rule that works the same way in inline links and link reference definitions.) [Whitespace] is allowed around the destination and title: . [link]( /uri "title" ) .
link
. But it is not allowed between the link text and the following parenthesis: . [link] (/uri) .
[link] (/uri)
. The link text may contain balanced brackets, but not unbalanced ones, unless they are escaped: . [link [foo [bar]]](/uri) .
link [foo [bar]]
. . [link] bar](/uri) .
[link] bar](/uri)
. . [link [bar](/uri) .
[link bar
. . [link \[bar](/uri) .
link [bar
. The link text may contain inline content: . [link *foo **bar** `#`*](/uri) .
link foo bar #
. . [![moon](moon.jpg)](/uri) .
. However, links may not contain other links, at any level of nesting. . [foo [bar](/uri)](/uri) .
[foo bar](/uri)
. . [foo *[bar [baz](/uri)](/uri)*](/uri) .
[foo [bar baz](/uri)](/uri)
. . ![[[foo](uri1)](uri2)](uri3) .
. These cases illustrate the precedence of link text grouping over emphasis grouping: . *[foo*](/uri) .
*foo*
. . [foo *bar](baz*) .
foo *bar
. Note that brackets that *aren't* part of links do not take precedence: . *foo [bar* baz] .
foo [bar baz]
. These cases illustrate the precedence of HTML tags, code spans, and autolinks over link grouping: . [foo .
[foo
. . [foo`](/uri)` .
[foo](/uri)
. . [foo .
[foohttp://example.com/?search=](uri)
. There are three kinds of [reference link](@reference-link)s: [full](#full-reference-link), [collapsed](#collapsed-reference-link), and [shortcut](#shortcut-reference-link). A [full reference link](@full-reference-link) consists of a [link text] immediately followed by a [link label] that [matches] a [link reference definition] elsewhere in the document. A [link label](@link-label) begins with a left bracket (`[`) and ends with the first right bracket (`]`) that is not backslash-escaped. Between these brackets there must be at least one [non-whitespace character]. Unescaped square bracket characters are not allowed in [link label]s. A link label can have at most 999 characters inside the square brackets. One label [matches](@matches) another just in case their normalized forms are equal. To normalize a label, perform the *Unicode case fold* and collapse consecutive internal [whitespace] to a single space. If there are multiple matching reference link definitions, the one that comes first in the document is used. (It is desirable in such cases to emit a warning.) The contents of the first link label are parsed as inlines, which are used as the link's text. The link's URI and title are provided by the matching [link reference definition]. Here is a simple example: . [foo][bar] [bar]: /url "title" .
foo
. The rules for the [link text] are the same as with [inline link]s. Thus: The link text may contain balanced brackets, but not unbalanced ones, unless they are escaped: . [link [foo [bar]]][ref] [ref]: /uri .
link [foo [bar]]
. . [link \[bar][ref] [ref]: /uri .
link [bar
. The link text may contain inline content: . [link *foo **bar** `#`*][ref] [ref]: /uri .
link foo bar #
. . [![moon](moon.jpg)][ref] [ref]: /uri .
. However, links may not contain other links, at any level of nesting. . [foo [bar](/uri)][ref] [ref]: /uri .
[foo bar]ref
. . [foo *bar [baz][ref]*][ref] [ref]: /uri .
[foo bar baz]ref
. (In the examples above, we have two [shortcut reference link]s instead of one [full reference link].) The following cases illustrate the precedence of link text grouping over emphasis grouping: . *[foo*][ref] [ref]: /uri .
*foo*
. . [foo *bar][ref] [ref]: /uri .
foo *bar
. These cases illustrate the precedence of HTML tags, code spans, and autolinks over link grouping: . [foo [ref]: /uri .
[foo
. . [foo`][ref]` [ref]: /uri .
[foo][ref]
. . [foo [ref]: /uri .
[foohttp://example.com/?search=][ref]
. Matching is case-insensitive: . [foo][BaR] [bar]: /url "title" .
foo
. Unicode case fold is used: . [Толпой][Толпой] is a Russian word. [ТОЛПОЙ]: /url .
Толпой is a Russian word.
. Consecutive internal [whitespace] is treated as one space for purposes of determining matching: . [Foo bar]: /url [Baz][Foo bar] .
Baz
. No [whitespace] is allowed between the [link text] and the [link label]: . [foo] [bar] [bar]: /url "title" .
[foo] bar
. . [foo] [bar] [bar]: /url "title" .
[foo] bar
. This is a departure from John Gruber's original Markdown syntax description, which explicitly allows whitespace between the link text and the link label. It brings reference links in line with [inline link]s, which (according to both original Markdown and this spec) cannot have whitespace after the link text. More importantly, it prevents inadvertent capture of consecutive [shortcut reference link]s. If whitespace is allowed between the link text and the link label, then in the following we will have a single reference link, not two shortcut reference links, as intended: ``` markdown [foo] [bar] [foo]: /url1 [bar]: /url2 ``` (Note that [shortcut reference link]s were introduced by Gruber himself in a beta version of `Markdown.pl`, but never included in the official syntax description. Without shortcut reference links, it is harmless to allow space between the link text and link label; but once shortcut references are introduced, it is too dangerous to allow this, as it frequently leads to unintended results.) When there are multiple matching [link reference definition]s, the first is used: . [foo]: /url1 [foo]: /url2 [bar][foo] .
bar
. Note that matching is performed on normalized strings, not parsed inline content. So the following does not match, even though the labels define equivalent inline content: . [bar][foo\!] [foo!]: /url .
[bar][foo!]
. [Link label]s cannot contain brackets, unless they are backslash-escaped: . [foo][ref[] [ref[]: /uri .
[foo][ref[]

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

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

[[[foo]]]: /url
. . [foo][ref\[] [ref\[]: /uri .
foo
. Note that in this example `]` is not backslash-escaped: . [bar\\]: /uri [bar\\] .
bar\
. A [link label] must contain at least one [non-whitespace character]: . [] []: /uri .
[]

[]: /uri
. . [ ] [ ]: /uri .
[ ]

[ ]: /uri
. A [collapsed reference link](@collapsed-reference-link) consists of a [link label] that [matches] a [link reference definition] elsewhere in the document, followed by the string `[]`. The contents of the first link label are parsed as inlines, which are used as the link's text. The link's URI and title are provided by the matching reference link definition. Thus, `[foo][]` is equivalent to `[foo][foo]`. . [foo][] [foo]: /url "title" .
foo
. . [*foo* bar][] [*foo* bar]: /url "title" .
foo bar
. The link labels are case-insensitive: . [Foo][] [foo]: /url "title" .
Foo
. As with full reference links, [whitespace] is not allowed between the two sets of brackets: . [foo] [] [foo]: /url "title" .
foo []
. A [shortcut reference link](@shortcut-reference-link) consists of a [link label] that [matches] a [link reference definition] elsewhere in the document and is not followed by `[]` or a link label. The contents of the first link label are parsed as inlines, which are used as the link's text. the link's URI and title are provided by the matching link reference definition. Thus, `[foo]` is equivalent to `[foo][]`. . [foo] [foo]: /url "title" .
foo
. . [*foo* bar] [*foo* bar]: /url "title" .
foo bar
. . [[*foo* bar]] [*foo* bar]: /url "title" .
[foo bar]
. . [[bar [foo] [foo]: /url .
[[bar foo
. The link labels are case-insensitive: . [Foo] [foo]: /url "title" .
Foo
. A space after the link text should be preserved: . [foo] bar [foo]: /url .
foo bar
. If you just want bracketed text, you can backslash-escape the opening bracket to avoid links: . \[foo] [foo]: /url "title" .
[foo]
. Note that this is a link, because a link label ends with the first following closing bracket: . [foo*]: /url *[foo*] .
*foo*
. Full references take precedence over shortcut references: . [foo][bar] [foo]: /url1 [bar]: /url2 .
foo
. In the following case `[bar][baz]` is parsed as a reference, `[foo]` as normal text: . [foo][bar][baz] [baz]: /url .
[foo]bar
. Here, though, `[foo][bar]` is parsed as a reference, since `[bar]` is defined: . [foo][bar][baz] [baz]: /url1 [bar]: /url2 .
foo baz
. Here `[foo]` is not parsed as a shortcut reference, because it is followed by a link label (even though `[bar]` is not defined): . [foo][bar][baz] [baz]: /url1 [foo]: /url2 .
[foo]bar
. ## Images Syntax for images is like the syntax for links, with one difference. Instead of [link text], we have an [image description](@image-description). The rules for this are the same as for [link text], except that (a) an image description starts with `![` rather than `[`, and (b) an image description may contain links. An image description has inline elements as its contents. When an image is rendered to HTML, this is standardly used as the image's `alt` attribute. . ![foo](/url "title") .
. . ![foo *bar*] [foo *bar*]: train.jpg "train & tracks" .
. . ![foo ![bar](/url)](/url2) .
. . ![foo [bar](/url)](/url2) .
. Though this spec is concerned with parsing, not rendering, it is recommended that in rendering to HTML, only the plain string content of the [image description] be used. Note that in the above example, the alt attribute's value is `foo bar`, not `foo [bar](/url)` or `foo bar`. Only the plain string content is rendered, without formatting. . ![foo *bar*][] [foo *bar*]: train.jpg "train & tracks" .
. . ![foo *bar*][foobar] [FOOBAR]: train.jpg "train & tracks" .
. . ![foo](train.jpg) .
. . My ![foo bar](/path/to/train.jpg "title" ) .
My
. . ![foo]() .
. . ![](/url) .
. Reference-style: . ![foo][bar] [bar]: /url .
. . ![foo][bar] [BAR]: /url .
. Collapsed: . ![foo][] [foo]: /url "title" .
. . ![*foo* bar][] [*foo* bar]: /url "title" .
. The labels are case-insensitive: . ![Foo][] [foo]: /url "title" .
. As with reference links, [whitespace] is not allowed between the two sets of brackets: . ![foo] [] [foo]: /url "title" .
[]
. Shortcut: . ![foo] [foo]: /url "title" .
. . ![*foo* bar] [*foo* bar]: /url "title" .
. Note that link labels cannot contain unescaped brackets: . ![[foo]] [[foo]]: /url "title" .
![[foo]]

[[foo]]: /url "title"
. The link labels are case-insensitive: . ![Foo] [foo]: /url "title" .
. If you just want bracketed text, you can backslash-escape the opening `!` and `[`: . \!\[foo] [foo]: /url "title" .
![foo]
. If you want a link after a literal `!`, backslash-escape the `!`: . \![foo] [foo]: /url "title" .
!foo
. ## Autolinks [Autolink](@autolink)s are absolute URIs and email addresses inside `<` and `>`. They are parsed as links, with the URL or email address as the link label. A [URI autolink](@uri-autolink) consists of `<`, followed by an [absolute URI] not containing `<`, followed by `>`. It is parsed as a link to the URI, with the URI as the link's label. An [absolute URI](@absolute-uri), for these purposes, consists of a [scheme] followed by a colon (`:`) followed by zero or more characters other than ASCII [whitespace] and control characters, `<`, and `>`. If the URI includes these characters, they must be percent-encoded (e.g. `%20` for a space). For purposes of this spec, a [scheme](@scheme) is any sequence of 2--32 characters beginning with an ASCII letter and followed by any combination of ASCII letters, digits, or the symbols plus ("+"), period ("."), or hyphen ("-"). Here are some valid autolinks: . .
http://foo.bar.baz
. . .
http://foo.bar.baz/test?q=hello&id=22&boolean
. . .
irc://foo.bar:2233/baz
. Uppercase is also fine: . .
MAILTO:FOO@BAR.BAZ
. Note that many strings that count as [absolute URI]s for purposes of this spec are not valid URIs, because their schemes are not registered or because of other problems with their syntax: . .
a+b+c:d
. . .
made-up-scheme://foo,bar
. . .
http://../
. . .
localhost:5001/foo
. Spaces are not allowed in autolinks: . .
<http://foo.bar/baz bim>
. Backslash-escapes do not work inside autolinks: . .
http://example.com/\[\
. An [email autolink](@email-autolink) consists of `<`, followed by an [email address], followed by `>`. The link's label is the email address, and the URL is `mailto:` followed by the email address. An [email address](@email-address), for these purposes, is anything that matches the [non-normative regex from the HTML5 spec](https://html.spec.whatwg.org/multipage/forms.html#e-mail-state-(type=email)): /^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])? (?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/ Examples of email autolinks: . .
foo@bar.example.com
. . .
foo+special@Bar.baz-bar0.com
. Backslash-escapes do not work inside email autolinks: . .
<foo+@bar.example.com>
. These are not autolinks: . <> .
<>
. . < http://foo.bar > .
< http://foo.bar >
. . .
<m:abc>
. . .
<foo.bar.baz>
. . http://example.com .
http://example.com
. . foo@bar.example.com .
foo@bar.example.com
. ## Raw HTML Text between `<` and `>` that looks like an HTML tag is parsed as a raw HTML tag and will be rendered in HTML without escaping. Tag and attribute names are not limited to current HTML tags, so custom tags (and even, say, DocBook tags) may be used. Here is the grammar for tags: A [tag name](@tag-name) consists of an ASCII letter followed by zero or more ASCII letters, digits, or hyphens (`-`). An [attribute](@attribute) consists of [whitespace], an [attribute name], and an optional [attribute value specification]. An [attribute name](@attribute-name) consists of an ASCII letter, `_`, or `:`, followed by zero or more ASCII letters, digits, `_`, `.`, `:`, or `-`. (Note: This is the XML specification restricted to ASCII. HTML5 is laxer.) An [attribute value specification](@attribute-value-specification) consists of optional [whitespace], a `=` character, optional [whitespace], and an [attribute value]. An [attribute value](@attribute-value) consists of an [unquoted attribute value], a [single-quoted attribute value], or a [double-quoted attribute value]. An [unquoted attribute value](@unquoted-attribute-value) is a nonempty string of characters not including spaces, `"`, `'`, `=`, `<`, `>`, or `` ` ``. A [single-quoted attribute value](@single-quoted-attribute-value) consists of `'`, zero or more characters not including `'`, and a final `'`. A [double-quoted attribute value](@double-quoted-attribute-value) consists of `"`, zero or more characters not including `"`, and a final `"`. An [open tag](@open-tag) consists of a `<` character, a [tag name], zero or more [attribute]s, optional [whitespace], an optional `/` character, and a `>` character. A [closing tag](@closing-tag) consists of the string ``. An [HTML comment](@html-comment) consists of ``, where *text* does not start with `>` or `->`, does not end with `-`, and does not contain `--`. (See the [HTML5 spec](http://www.w3.org/TR/html5/syntax.html#comments).) A [processing instruction](@processing-instruction) consists of the string ``, and the string `?>`. A [declaration](@declaration) consists of the string ``, and the character `>`. A [CDATA section](@cdata-section) consists of the string ``, and the string `]]>`. An [HTML tag](@html-tag) consists of an [open tag], a [closing tag], an [HTML comment], a [processing instruction], a [declaration], or a [CDATA section]. Here are some simple open tags: . .
. Empty elements: . .
. [Whitespace] is allowed: . .
. With attributes: . .
. Custom tag names can be used: . Foo .
Foo
. Illegal tag names, not parsed as HTML: . <33> <__> .
<33> <__>
. Illegal attribute names: . .
<a h*#ref="hi">
. Illegal attribute values: . .
</a href="foo">
. Comments: . foo .
foo
. . foo .
foo 
. Not comments: . foo foo --> foo .
foo 

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

Foo

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foo

foo

foo

foo

foo

foo bar *baz*

foo

foo

foo

foo

foo

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foo

foo

foo

foo ### b

foo#

foo ###

foo ###

foo #

foo

baz

Foo bar

Foo bar

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Foo\

`Foo

<a title="a lot

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foo

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aaa

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foo bar baz