GitHub Flavored Markdown, often shortened as GFM, is the dialect of Markdown that is currently supported for user content on GitHub.com and GitHub Enterprise.
This formal specification, based on the CommonMark Spec, defines the syntax and semantics of this dialect.
GFM is a strict superset of CommonMark. All the features which are supported in GitHub user content and that are not specified on the original CommonMark Spec are hence known as extensions, and highlighted as such.
While GFM supports a wide range of inputs, it’s worth noting that GitHub.com and GitHub Enterprise perform additional post-processing and sanitization after GFM is converted to HTML to ensure security and consistency of the website.
Markdown is a plain text format for writing structured documents,
based on conventions for indicating formatting in email
and usenet posts. It was developed by John Gruber (with
help from Aaron Swartz) and released in 2004 in the form of a
syntax description
and a Perl script (Markdown.pl) for converting Markdown to
HTML. In the next decade, dozens of implementations were
developed in many languages. Some extended the original
Markdown syntax with conventions for footnotes, tables, and
other document elements. Some allowed Markdown documents to be
rendered in formats other than HTML. Websites like Reddit,
StackOverflow, and GitHub had millions of people using Markdown.
And Markdown started to be used beyond the web, to author books,
articles, slide shows, letters, and lecture notes.
What distinguishes Markdown from many other lightweight markup syntaxes, which are often easier to write, is its readability. As Gruber writes:
The overriding design goal for Markdown’s formatting syntax is to make it as readable as possible. The idea is that a Markdown-formatted document should be publishable as-is, as plain text, without looking like it’s been marked up with tags or formatting instructions. (http://daringfireball.net/projects/markdown/)
The point can be illustrated by comparing a sample of AsciiDoc with an equivalent sample of Markdown. Here is a sample of AsciiDoc from the AsciiDoc manual:
1. List item one.
+
List item one continued with a second paragraph followed by an
Indented block.
+
.................
$ ls *.sh
$ mv *.sh ~/tmp
.................
+
List item continued with a third paragraph.
2. List item two continued with an open block.
+
--
This paragraph is part of the preceding list item.
a. This list is nested and does not require explicit item
continuation.
+
This paragraph is part of the preceding list item.
b. List item b.
This paragraph belongs to item two of the outer list.
--
And here is the equivalent in Markdown:
1. List item one.
List item one continued with a second paragraph followed by an
Indented block.
$ ls *.sh
$ mv *.sh ~/tmp
List item continued with a third paragraph.
2. List item two continued with an open block.
This paragraph is part of the preceding list item.
1. This list is nested and does not require explicit item continuation.
This paragraph is part of the preceding list item.
2. List item b.
This paragraph belongs to item two of the outer list.
The AsciiDoc version is, arguably, easier to write. You don’t need to worry about indentation. But the Markdown version is much easier to read. The nesting of list items is apparent to the eye in the source, not just in the processed document.
John Gruber’s canonical description of Markdown’s syntax does not specify the syntax unambiguously. Here are some examples of questions it does not answer:
How much indentation is needed for a sublist? The spec says that
continuation paragraphs need to be indented four spaces, but is
not fully explicit about sublists. It is natural to think that
they, too, must be indented four spaces, but Markdown.pl does
not require that. This is hardly a “corner case,” and divergences
between implementations on this issue often lead to surprises for
users in real documents. (See this comment by John
Gruber.)
Is a blank line needed before a block quote or heading? Most implementations do not require the blank line. However, this can lead to unexpected results in hard-wrapped text, and also to ambiguities in parsing (note that some implementations put the heading inside the blockquote, while others do not). (John Gruber has also spoken in favor of requiring the blank lines.)
Is a blank line needed before an indented code block?
(Markdown.pl requires it, but this is not mentioned in the
documentation, and some implementations do not require it.)
paragraph
code?
What is the exact rule for determining when list items get
wrapped in tags? Can a list be partially “loose” and partially
“tight”? What should we do with a list like this?
1. one
2. two
3. three
Or this?
1. one
- a
- b
2. two
(There are some relevant comments by John Gruber here.)
Can list markers be indented? Can ordered list markers be right-aligned?
8. item 1
9. item 2
10. item 2a
Is this one list with a thematic break in its second item, or two lists separated by a thematic break?
* a
* * * * *
* b
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.)
1. fee
2. fie
- foe
- fum
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 ?
[a backtick (`)](/url) and [another backtick (`)](/url).
What are the precedence rules for markers of emphasis and strong emphasis? For example, how should the following be parsed?
*foo *bar* baz*
What are the precedence rules between block-level and inline-level structure? For example, how should the following be parsed?
- `a long code span can contain a hyphen like this
- and it can screw things up`
Can list items include section headings? (Markdown.pl does not
allow this, but does allow blockquotes to include headings.)
- # Heading
Can list items be empty?
* a
*
* b
Can link references be defined inside block quotes or list items?
> Blockquote [foo].
>
> [foo]: /url
If there are multiple definitions for the same reference, which takes precedence?
[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.
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.
Any sequence of characters is a valid CommonMark document.
A character is a Unicode code point. Although some code points (for example, combining accents) do not correspond to characters in an intuitive sense, all code points count as characters for purposes of this spec.
This spec does not specify an encoding; it thinks of lines as composed of characters rather than bytes. A conforming parser may be limited to a certain encoding.
A line is a sequence of zero or more characters
other than newline (U+000A) or carriage return (U+000D),
followed by a line ending or by the end of file.
A line ending is a newline (U+000A), a carriage return
(U+000D) not followed by a newline, or a carriage return and a
following newline.
A line containing no characters, or a line containing only spaces
(U+0020) or tabs (U+0009), is called a blank line.
The following definitions of character classes will be used in this spec:
A whitespace character is a space
(U+0020), tab (U+0009), newline (U+000A), line tabulation (U+000B),
form feed (U+000C), or carriage return (U+000D).
Whitespace is a sequence of one or more whitespace characters.
A Unicode whitespace character is
any code point in the Unicode Zs general category, or a tab (U+0009),
carriage return (U+000D), newline (U+000A), or form feed
(U+000C).
Unicode whitespace is a sequence of one or more Unicode whitespace characters.
A space is U+0020.
A non-whitespace character is any character that is not a whitespace character.
An ASCII punctuation character
is !, ", #, $, %, &, ', (, ),
*, +, ,, -, ., / (U+0021–2F),
:, ;, <, =, >, ?, @ (U+003A–0040),
[, \, ], ^, _, ` (U+005B–0060),
{, |, }, or ~ (U+007B–007E).
A punctuation character is an ASCII
punctuation character or anything in
the general Unicode categories Pc, Pd, Pe, Pf, Pi, Po, or Ps.
Tabs in lines are not expanded to spaces. However, in contexts where whitespace helps to define block structure, tabs behave as if they were replaced by spaces with a tab stop of 4 characters.
Thus, for example, a tab can be used instead of four spaces in an indented code block. (Note, however, that internal tabs are passed through as literal tabs, not expanded to spaces.)
In the following example, a continuation paragraph of a list item is indented with a tab; this has exactly the same effect as indentation with four spaces would:
Normally the > that begins a block quote may be followed
optionally by a space, which is not considered part of the
content. In the following case > is followed by a tab,
which is treated as if it were expanded into three spaces.
Since one of these spaces is considered part of the
delimiter, foo is considered to be indented six spaces
inside the block quote context, so we get an indented
code block starting with two spaces.
For security reasons, the Unicode character U+0000 must be replaced
with the REPLACEMENT CHARACTER (U+FFFD).
We can think of a document as a sequence of blocks—structural elements like paragraphs, block quotations, lists, headings, rules, and code blocks. Some blocks (like block quotes and list items) contain other blocks; others (like headings and paragraphs) contain inline content—text, links, emphasized text, images, code spans, and so on.
Indicators of block structure always take precedence over indicators of inline structure. So, for example, the following is a list with two items, not a list with one item containing a code span:
This means that parsing can proceed in two steps: first, the block structure of the document can be discerned; second, text lines inside paragraphs, headings, and other block constructs can be parsed for inline structure. The second step requires information about link reference definitions that will be available only at the end of the first step. Note that the first step requires processing lines in sequence, but the second can be parallelized, since the inline parsing of one block element does not affect the inline parsing of any other.
We can divide blocks into two types: container blocks, which can contain other blocks, and leaf blocks, which cannot.
This section describes the different kinds of leaf block that make up a Markdown document.
A line consisting of 0-3 spaces of indentation, followed by a sequence
of three or more matching -, _, or * characters, each followed
optionally by any number of spaces or tabs, forms a
thematic break.
Wrong characters:
Not enough characters:
One to three spaces indent are allowed:
Four spaces is too many:
More than three characters may be used:
Spaces are allowed between the characters:
Spaces are allowed at the end:
However, no other characters may occur in the line:
It is required that all of the non-whitespace characters be the same. So, this is not a thematic break:
Thematic breaks do not need blank lines before or after:
Thematic breaks can interrupt a paragraph:
If a line of dashes that meets the above conditions for being a thematic break could also be interpreted as the underline of a setext heading, the interpretation as a setext heading takes precedence. Thus, for example, this is a setext heading, not a paragraph followed by a thematic break:
When both a thematic break and a list item are possible interpretations of a line, the thematic break takes precedence:
If you want a thematic break in a list item, use a different bullet:
An ATX heading
consists of a string of characters, parsed as inline content, between an
opening sequence of 1–6 unescaped # characters and an optional
closing sequence of any number of unescaped # characters.
The opening sequence of # characters must be followed by a
space or by the end of line. The optional closing sequence of #s must be
preceded by a space and may be followed by spaces only. The opening
# character may be indented 0-3 spaces. The raw contents of the
heading are stripped of leading and trailing spaces before being parsed
as inline content. The heading level is equal to the number of #
characters in the opening sequence.
Simple headings:
More than six # characters is not a heading:
At least one space is required between the # characters and the
heading’s contents, unless the heading is empty. Note that many
implementations currently do not require the space. However, the
space was required by the
original ATX implementation,
and it helps prevent things like the following from being parsed as
headings:
This is not a heading, because the first # is escaped:
Contents are parsed as inlines:
Leading and trailing whitespace is ignored in parsing inline content:
One to three spaces indentation are allowed:
Four spaces are too much:
A closing sequence of # characters is optional:
It need not be the same length as the opening sequence:
Spaces are allowed after the closing sequence:
A sequence of # characters with anything but spaces following it
is not a closing sequence, but counts as part of the contents of the
heading:
The closing sequence must be preceded by a space:
Backslash-escaped # characters do not count as part
of the closing sequence:
ATX headings need not be separated from surrounding content by blank lines, and they can interrupt paragraphs:
ATX headings can be empty:
A setext heading consists of one or more lines of text, each containing at least one non-whitespace character, with no more than 3 spaces indentation, followed by a setext heading underline. The lines of text must be such that, were they not followed by the setext heading underline, they would be interpreted as a paragraph: they cannot be interpretable as a code fence, ATX heading, block quote, thematic break, list item, or HTML block.
A setext heading underline is a sequence of
= characters or a sequence of - characters, with no more than 3
spaces indentation and any number of trailing spaces. If a line
containing a single - can be interpreted as an
empty list items, it should be interpreted this way
and not as a setext heading underline.
The heading is a level 1 heading if = characters are used in
the setext heading underline, and a level 2 heading if -
characters are used. The contents of the heading are the result
of parsing the preceding lines of text as CommonMark inline
content.
In general, a setext heading need not be preceded or followed by a blank line. However, it cannot interrupt a paragraph, so when a setext heading comes after a paragraph, a blank line is needed between them.
Simple examples:
The content of the header may span more than one line:
The contents are the result of parsing the headings’s raw content as inlines. The heading’s raw content is formed by concatenating the lines and removing initial and final whitespace.
The underlining can be any length:
The heading content can be indented up to three spaces, and need not line up with the underlining:
Four spaces indent is too much:
The setext heading underline can be indented up to three spaces, and may have trailing spaces:
Four spaces is too much:
The setext heading underline cannot contain internal spaces:
Trailing spaces in the content line do not cause a line break:
Nor does a backslash at the end:
Since indicators of block structure take precedence over indicators of inline structure, the following are setext headings:
The setext heading underline cannot be a lazy continuation line in a list item or block quote:
A blank line is needed between a paragraph and a following setext heading, since otherwise the paragraph becomes part of the heading’s content:
But in general a blank line is not required before or after setext headings:
Setext headings cannot be empty:
Setext heading text lines must not be interpretable as block constructs other than paragraphs. So, the line of dashes in these examples gets interpreted as a thematic break:
If you want a heading with > foo as its literal text, you can
use backslash escapes:
Compatibility note: Most existing Markdown implementations do not allow the text of setext headings to span multiple lines. But there is no consensus about how to interpret
Foo
bar
---
baz
One can find four different interpretations:
We find interpretation 4 most natural, and interpretation 4 increases the expressive power of CommonMark, by allowing multiline headings. Authors who want interpretation 1 can put a blank line after the first paragraph:
Authors who want interpretation 2 can put blank lines around the thematic break,
or use a thematic break that cannot count as a setext heading underline, such as
Authors who want interpretation 3 can use backslash escapes:
An indented code block is composed of one or more indented chunks separated by blank lines. An indented chunk is a sequence of non-blank lines, each indented four or more spaces. The contents of the code block are the literal contents of the lines, including trailing line endings, minus four spaces of indentation. An indented code block has no info string.
An indented code block cannot interrupt a paragraph, so there must be a blank line between a paragraph and a following indented code block. (A blank line is not needed, however, between a code block and a following paragraph.)
If there is any ambiguity between an interpretation of indentation as a code block and as indicating that material belongs to a list item, the list item interpretation takes precedence:
The contents of a code block are literal text, and do not get parsed as Markdown:
Here we have three chunks separated by blank lines:
Any initial spaces beyond four will be included in the content, even in interior blank lines:
An indented code block cannot interrupt a paragraph. (This allows hanging indents and the like.)
However, any non-blank line with fewer than four leading spaces ends the code block immediately. So a paragraph may occur immediately after indented code:
And indented code can occur immediately before and after other kinds of blocks:
The first line can be indented more than four spaces:
Blank lines preceding or following an indented code block are not included in it:
Trailing spaces are included in the code block’s content:
A code fence is a sequence
of at least three consecutive backtick characters (`) or
tildes (~). (Tildes and backticks cannot be mixed.)
A fenced code block
begins with a code fence, indented no more than three spaces.
The line with the opening code fence may optionally contain some text following the code fence; this is trimmed of leading and trailing whitespace and called the info string. If the info string comes after a backtick fence, it may not contain any backtick characters. (The reason for this restriction is that otherwise some inline code would be incorrectly interpreted as the beginning of a fenced code block.)
The content of the code block consists of all subsequent lines, until a closing code fence of the same type as the code block began with (backticks or tildes), and with at least as many backticks or tildes as the opening code fence. If the leading code fence is indented N spaces, then up to N spaces of indentation are removed from each line of the content (if present). (If a content line is not indented, it is preserved unchanged. If it is indented less than N spaces, all of the indentation is removed.)
The closing code fence may be indented up to three spaces, and may be followed only by spaces, which are ignored. If the end of the containing block (or document) is reached and no closing code fence has been found, the code block contains all of the lines after the opening code fence until the end of the containing block (or document). (An alternative spec would require backtracking in the event that a closing code fence is not found. But this makes parsing much less efficient, and there seems to be no real down side to the behavior described here.)
A fenced code block may interrupt a paragraph, and does not require a blank line either before or after.
The content of a code fence is treated as literal text, not parsed
as inlines. The first word of the info string is typically used to
specify the language of the code sample, and rendered in the class
attribute of the code tag. However, this spec does not mandate any
particular treatment of the info string.
Here is a simple example with backticks:
With tildes:
Fewer than three backticks is not enough:
The closing code fence must use the same character as the opening fence:
The closing code fence must be at least as long as the opening fence:
Unclosed code blocks are closed by the end of the document (or the enclosing block quote or list item):
A code block can have all empty lines as its content:
A code block can be empty:
Fences can be indented. If the opening fence is indented, content lines will have equivalent opening indentation removed, if present:
Four spaces indentation produces an indented code block:
Closing fences may be indented by 0-3 spaces, and their indentation need not match that of the opening fence:
This is not a closing fence, because it is indented 4 spaces:
Code fences (opening and closing) cannot contain internal spaces:
Fenced code blocks can interrupt paragraphs, and can be followed directly by paragraphs, without a blank line between:
Other blocks can also occur before and after fenced code blocks without an intervening blank line:
An info string can be provided after the opening code fence.
Although this spec doesn’t mandate any particular treatment of
the info string, the first word is typically used to specify
the language of the code block. In HTML output, the language is
normally indicated by adding a class to the code element consisting
of language- followed by the language name.
~~~~ ruby startline=3 $%@#$
def foo(x)
return 3
end
~~~~~~~
class="language-ruby">def foo(x)
return 3
end
Info strings for backtick code blocks cannot contain backticks:
Info strings for tilde code blocks can contain backticks and tildes:
Closing code fences cannot have info strings:
An HTML block is a group of lines that is treated as raw HTML (and will not be escaped in HTML output).
There are seven kinds of HTML block, which can be defined by their start and end conditions. The block begins with a line that meets a start condition (after up to three spaces optional indentation). It ends with the first subsequent line that meets a matching end condition, or the last line of the document, or the last line of the container block containing the current HTML block, if no line is encountered that meets the end condition. If the first line meets both the start condition and the end condition, the block will contain just that line.
Start condition: line begins with the string >, or the end of the line.
End condition: line contains an end tag
, , or (case-insensitive; it
need not match the start tag).
Start condition: line begins with the string .
Start condition: line begins with the string .
End condition: line contains the string ?>.
Start condition: line begins with the string
followed by an uppercase ASCII letter.
End condition: line contains the character >.
Start condition: line begins with the string
.
End condition: line contains the string ]]>.
Start condition: line begins the string < or
followed by one of the strings (case-insensitive) address,
article, aside, base, basefont, blockquote, body,
caption, center, col, colgroup, dd, details, dialog,
dir, div, dl, dt, fieldset, figcaption, figure,
footer, form, frame, frameset,
h1, h2, h3, h4, h5, h6, head, header, hr,
html, iframe, legend, li, link, main, menu, menuitem,
nav, noframes, ol, optgroup, option, p, param,
section, source, summary, table, tbody, td,
tfoot, th, thead, title, tr, track, ul, followed
by whitespace, the end of the line, the string >, or
the string />.
End condition: line is followed by a blank line.
Start condition: line begins with a complete open tag
(with any tag name other than script,
style, or pre) or a complete closing tag,
followed only by whitespace or the end of the line.
End condition: line is followed by a blank line.
HTML blocks continue until they are closed by their appropriate end condition, or the last line of the document or other container block. This means any HTML within an HTML block that might otherwise be recognised as a start condition will be ignored by the parser and passed through as-is, without changing the parser’s state.
For instance, In this case, the HTML block is terminated by the newline — the All types of HTML blocks except type 7 may interrupt
a paragraph. Blocks of type 7 may not interrupt a paragraph.
(This restriction is intended to prevent unwanted interpretation
of long tags inside a wrapped paragraph as starting HTML blocks.) Some simple examples follow. Here are some basic HTML blocks
of type 6: A block can also start with a closing tag: Here we have two HTML blocks with a Markdown paragraph between them: Markdown The tag on the first line can be partial, as long
as it is split where there would be whitespace: An open tag need not be closed: bar A partial tag need not even be completed (garbage
in, garbage out): The initial tag doesn’t even need to be a valid
tag, as long as it starts like one: In type 6 blocks, the initial tag need not be on a line by
itself: 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: 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): In type 7 blocks, the tag name can be anything: These rules are designed to allow us to work with tags that
can function as either block-level or inline-level tags.
The In this case, we get a raw HTML block that just includes
the Finally, in this case, the HTML tags designed to contain literal content
( A pre tag (type 1): okay A script tag (type 1): okay 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
or list item): Note that anything on the last line after the
end tag will be included in the HTML block: A comment (type 2): A processing instruction (type 3): A declaration (type 4): CDATA (type 5): okay The opening tag can be indented 1-3 spaces, but not 4: An HTML block of types 1–6 can interrupt a paragraph, and need not be
preceded by a blank line. However, a following blank line is needed, except at the end of
a document, and except for blocks of types 1–5, above: HTML blocks of type 7 cannot interrupt a paragraph: This rule differs from John Gruber’s original Markdown syntax
specification, which says: The only restrictions are that block-level HTML elements —
e.g. In some ways Gruber’s rule is more restrictive than the one given
here: 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: Some Markdown implementations have adopted a convention of
interpreting content inside tags as text if the open tag has
the attribute 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: 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: Fortunately, blank lines are usually not necessary and can be
deleted. The exception is inside A link reference definition
consists of a link label, indented up to three spaces, followed
by a colon ( A link reference definition
does not correspond to a structural element of a document. Instead, it
defines a label which can be used in reference links
and reference-style images elsewhere in the document. Link
reference definitions can come either before or after the links that use
them. The title may extend over multiple lines: However, it may not contain a blank line: The title may be omitted: The link destination may not be omitted: However, an empty link destination may be specified using
angle brackets: The title must be separated from the link destination by
whitespace: Both title and destination can contain backslash escapes
and literal backslashes: A link can come before its corresponding definition: If there are several matching definitions, the first one takes
precedence: As noted in the section on Links, matching of labels is
case-insensitive (see matches). Here is a link reference definition with no corresponding link.
It contributes nothing to the document. Here is another one: This is not a link reference definition, because there are
non-whitespace characters after the title: This is a link reference definition, but it has no title: This is not a link reference definition, because it is indented
four spaces: This is not a link reference definition, because it occurs inside
a code block: A link reference definition cannot interrupt a paragraph. However, it can directly follow other block elements, such as headings
and thematic breaks, and it need not be followed by a blank line. Several link reference definitions
can occur one after another, without intervening blank lines. Link reference definitions can occur
inside block containers, like lists and block quotations. They
affect the entire document, not just the container in which they
are defined: Whether something is a link reference definition is
independent of whether the link reference it defines is
used in the document. Thus, for example, the following
document contains just a link reference definition, and
no visible content: A sequence of non-blank lines that cannot be interpreted as other
kinds of blocks forms a paragraph.
The contents of the paragraph are the result of parsing the
paragraph’s raw content as inlines. The paragraph’s raw content
is formed by concatenating the lines and removing initial and final
whitespace. A simple example with two paragraphs: Paragraphs can contain multiple lines, but no blank lines: Multiple blank lines between paragraph have no effect: Leading spaces are skipped: Lines after the first may be indented any amount, since indented
code blocks cannot interrupt paragraphs. However, the first line may be indented at most three spaces,
or an indented code block will be triggered: 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: Blank lines between block-level elements are ignored,
except for the role they play in determining whether a list
is tight or loose. Blank lines at the beginning and end of the document are also ignored. GFM enables the A table is an arrangement of data with rows and columns, consisting of a
single header row, a delimiter row separating the header from the data, and
zero or more data rows. Each row consists of cells containing arbitrary text, in which inlines are
parsed, separated by pipes ( The delimiter row consists of cells whose only content are hyphens ( Cells in one column don’t need to match length, though it’s easier to read if
they are. Likewise, use of leading and trailing pipes may be inconsistent: Include a pipe in a cell’s content by escaping it, including inside other
inline spans: The table is broken at the first empty line, or beginning of another
block-level structure: The header row must match the delimiter row in the number of cells. If not,
a table will not be recognized: The remainder of the table’s rows may vary in the number of cells. If there
are a number of cells fewer than the number of cells in the header row, empty
cells are inserted. If there are greater, the excess is ignored: If there are no rows in the body, no 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.) A block quote marker
consists of 0-3 spaces of initial indent, plus (a) the character The following rules define block quotes: 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 containing Bs. Laziness. If a string of lines Ls constitute a block
quote with contents Bs, then the result of deleting
the initial block quote marker from one or
more lines in which the next non-whitespace character after the block
quote marker is paragraph continuation
text is a block quote with Bs as its content.
Paragraph continuation text is text
that will be parsed as part of the content of a paragraph, but does
not occur at the beginning of the paragraph. 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. Here is a simple example: The spaces after the The Four spaces gives us a code block: The Laziness clause allows us to omit the A block quote can contain some lazy and some non-lazy
continuation lines: Laziness only applies to lines that would have been continuations of
paragraphs had they been prepended with block quote markers.
For example, the without changing the meaning: Similarly, if we omit the then the block quote ends after the first line: For the same reason, we can’t omit the Note that in the following case, we have a lazy
continuation line: To see why, note that in the A block quote can be empty: A block quote can have initial or final blank lines: A blank line always separates block quotes: (Most current Markdown implementations, including John Gruber’s
original Consecutiveness means that if we put these block quotes together,
we get a single block quote: To get a block quote with two paragraphs, use: Block quotes can interrupt paragraphs: In general, blank lines are not needed before or after block
quotes: However, because of laziness, a blank line is needed between
a block quote and a following paragraph: It is a consequence of the Laziness rule that any number
of initial When including an indented code block in a block quote,
remember that the block quote marker includes
both the A list marker is a
bullet list marker or an ordered list marker. A bullet list marker
is a An ordered list marker
is a sequence of 1–9 arabic digits ( The following rules define list items: Basic case. If a sequence of lines Ls constitute a sequence of
blocks Bs starting with a non-whitespace character, and M is a
list marker of width W followed by 1 ≤ N ≤ 4 spaces, then the result
of prepending M and the following spaces to the first line of
Ls, and indenting subsequent lines of Ls by W + N spaces, is a
list item with Bs as its contents. The type of the list item
(bullet or ordered) is determined by the type of its list marker.
If the list item is ordered, then it is also assigned a start
number, based on the ordered list marker. Exceptions: For example, let Ls be the lines A paragraph
with two lines. A block quote. And let M be the marker A paragraph
with two lines. 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: 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: Here The converse is also possible. In the following example, the word Note that at least one space is needed between the list marker and
any following content, so these are not list items: A list item may contain blocks that are separated by more than
one blank line. A list item may contain any kind of block: A list item that contains an indented code block will preserve
empty lines within the code block verbatim. Note that ordered list start numbers must be nine digits or less: A start number may begin with 0s: A start number may not be negative: 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: And in this case it is 11 spaces: 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: Note that an additional space indent is interpreted as space
inside the code block: 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: 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: Here are some list items that start with a blank line but are not empty: When the list item starts with a blank line, the number of spaces
following the list marker doesn’t change the required indentation: A list item can begin with at most one blank line.
In the following example, Here is an empty bullet list item: It does not matter whether there are spaces following the list marker: Here is an empty ordered list item: A list may start or end with an empty list item: However, an empty list item cannot interrupt a paragraph: Indented one space: A paragraph
with two lines. A block quote. Indented two spaces: A paragraph
with two lines. A block quote. Indented three spaces: A paragraph
with two lines. A block quote. Four spaces indent gives a code block: Here is an example with lazy continuation lines: A paragraph
with two lines. A block quote. Indentation can be partially deleted: These examples show how laziness can work in nested structures: 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: One is not enough: Here we need four, because the list marker is wider: Three is not enough: A list may be the first block in a list item: A list item can contain a heading: John Gruber’s Markdown spec says the following about list items: “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.” “To make lists look nice, you can wrap items with hanging indents….
But if you don’t want to, you don’t have to.” “List items may consist of multiple paragraphs. Each subsequent
paragraph in a list item must be indented by either 4 spaces or one
tab.” “It looks nice if you indent every line of the subsequent paragraphs,
but here again, Markdown will allow you to be lazy.” “To put a blockquote within a list item, the blockquote’s “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 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 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 should be parsed as two lists with an intervening paragraph, bar as the four-space rule demands, rather than a single list, foo bar 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,
as a single list item, with one two and similarly as 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 Arguably this text does read like a list item with 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 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. GFM enables the A task list item is a list item where the first block in it
is a paragraph which begins with a task list item marker and at least one
whitespace character before any other content. A task list item marker consists of an optional number of spaces, a left
bracket ( When rendered, the task list item marker is replaced with a semantic checkbox element;
in an HTML output, this would be an If the character between the brackets is a whitespace character, the checkbox
is unchecked. Otherwise, the checkbox is checked. This spec does not define how the checkbox elements are interacted with: in practice,
implementors are free to render the checkboxes as disabled or inmutable elements,
or they may dynamically handle dynamic interactions (i.e. checking, unchecking) in
the final rendered document. Task lists can be arbitrarily nested: A list is a sequence of one or more
list items of the same type. The list items
may be separated by any number of blank lines. Two list items are of the same type
if they begin with a list marker of the same type.
Two list markers are of the
same type if (a) they are bullet list markers using the same character
( A list is an ordered list
if its constituent list items begin with
ordered list markers, and a
bullet list if its constituent list
items begin with bullet list markers. The start number
of an ordered list is determined by the list number of
its initial list item. The numbers of subsequent list items are
disregarded. A list is loose if any of its constituent
list items are separated by blank lines, or if any of its constituent
list items directly contain two block-level elements with a blank line
between them. Otherwise a list is tight.
(The difference in HTML output is that paragraphs in a loose list are
wrapped in Changing the bullet or ordered list delimiter starts a new list: In CommonMark, a list can interrupt a paragraph. That is,
no blank line is needed to separate a paragraph from a following
list: Oddly, though, In CommonMark, we do allow lists to interrupt paragraphs, for
two reasons. First, it is natural and not uncommon for people
to start lists without blank lines: Second, we are attracted to a principle of uniformity:
if a chunk of text has a certain
meaning, it will continue to have the same meaning when put into a
container block (such as a list item or blockquote). (Indeed, the spec for list items and block quotes presupposes
this principle.) This principle implies that if 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 by itself should be a paragraph followed by a nested sublist. Since it is well established Markdown practice to allow lists to
interrupt paragraphs inside list items, the principle of
uniformity requires us to allow this outside list items as
well. (reStructuredText
takes a different approach, requiring blank lines before lists
even inside other list items.) In order to solve of unwanted lists in paragraphs with
hard-wrapped numerals, we allow only lists starting with The number of windows in my house is
14. The number of doors is 6. We may still get an unintended result in cases like The number of windows in my house is but this rule should prevent most spurious list captures. There can be any number of blank lines between items: To separate consecutive lists of the same type, or to separate a
list from an indented code block that would otherwise be parsed
as a subparagraph of the final list item, you can insert a blank HTML
comment: 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: Note, however, that list items may not be indented more than
three spaces. Here And here, This is a loose list, because there is a blank line between
two of the list items: So is this, with a empty second item: 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: This is a tight list, because the blank lines are in a code block: 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: This is a tight list, because the blank line is inside the
block quote: This list is tight, because the consecutive block elements
are not separated by blank lines: A single-paragraph list is tight: This list is loose, because of the blank line between the
two block elements in the list item: Here the outer list is loose, the inner list tight: 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 Any ASCII punctuation character may be backslash-escaped: !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~ Backslashes before other characters are treated as literal
backslashes: Escaped characters are treated as regular characters and do
not have their usual Markdown meanings: *not emphasized*
<br/> not a tag
[not a link](/foo)
`not code`
1. not a list
* not a list
# not a heading
[foo]: /url "not a reference"
ö not a character entity If a backslash is itself escaped, the following character is not: A backslash at the end of the line is a hard line break: Backslash escapes do not work in code blocks, code spans, autolinks, or
raw HTML: But they work in all other contexts, including URLs and link titles,
link references, and info strings in fenced code blocks: Valid HTML entity references and numeric character references
can be used in place of the corresponding Unicode character,
with the following exceptions: Entity and character references are not recognized in code
blocks and code spans. Entity and character references cannot stand in place of
special characters that define structural elements in
CommonMark. For example, although Conforming CommonMark parsers need not store information about
whether a particular character was represented in the source
using a Unicode character or an entity reference. Entity references consist of Decimal numeric character
references
consist of Hexadecimal numeric character
references consist of Here are some nonentities:   &x; &#; &#x;
�
&#abcdef0;
&ThisIsNotDefined; &hi?; Although HTML5 does accept some entity references
without a trailing semicolon (such as Strings that are not on the list of HTML5 named entities are not
recognized as entity references either: Entity and numeric character references are recognized in any
context besides code spans or code blocks, including
URLs, link titles, and fenced code block info strings: Entity and numeric character references are treated as literal
text in code spans and code blocks: Entity and numeric character references cannot be used
in place of symbols indicating structure in CommonMark
documents. A backtick string
is a string of one or more backtick characters ( A code span begins with a backtick string and ends with
a backtick string of equal length. The contents of the code span are
the characters between the two backtick strings, normalized in the
following ways: This is a simple code span: Here two backticks are used, because the code contains a backtick.
This example also illustrates stripping of a single leading and
trailing space: This example shows the motivation for stripping leading and trailing
spaces: Note that only one space is stripped: The stripping only happens if the space is on both
sides of the string: Only spaces, and not unicode whitespace in general, are
stripped in this way: No stripping occurs if the code span contains only spaces: Line endings are treated like spaces: Interior spaces are not collapsed: Note that browsers will typically collapse consecutive spaces
when rendering Note that backslash escapes do not work in code spans. All backslashes
are treated literally: 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 And this is not parsed as a link: Code spans, HTML tags, and autolinks have the same precedence.
Thus, this is code: But this is an HTML tag: And this is code: But this is an autolink: When a backtick string is not closed by a matching backtick string,
we just have literal backticks: The following case also illustrates the need for opening and
closing backtick strings to be equal in length: John Gruber’s original Markdown syntax
description says: Markdown treats asterisks ( This is enough for most users, but these rules leave much undecided,
especially when it comes to nested emphasis. The original
The following patterns are less widely supported, but the intent
is clear and they are useful (especially in contexts like bibliography
entries): Many implementations have also restricted intraword emphasis to
the The rules given below capture all of these patterns, while allowing
for efficient parsing strategies that do not backtrack. First, some definitions. A delimiter run is either
a sequence of one or more A left-flanking delimiter run is
a delimiter run that is (1) not followed by Unicode whitespace,
and either (2a) not followed by a punctuation character, or
(2b) followed by a punctuation character and
preceded by Unicode whitespace or a punctuation character.
For purposes of this definition, the beginning and the end of
the line count as Unicode whitespace. A right-flanking delimiter run is
a delimiter run that is (1) not preceded by Unicode whitespace,
and either (2a) not preceded by a punctuation character, or
(2b) preceded by a punctuation character and
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: right-flanking but not left-flanking: Both left and right-flanking: Neither left nor right-flanking: (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.
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: A single A single A single A single A double A double A double A double Emphasis begins with a delimiter that can open emphasis and ends
with a delimiter that can close emphasis, and that uses the same
character ( 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
( A literal A literal Where rules 1–12 above are compatible with multiple parsings,
the following principles resolve ambiguity: The number of nestings should be minimized. Thus, for example,
an interpretation An interpretation 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,
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,
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, These rules can be illustrated through a series of examples. Rule 1: This is not emphasis, because the opening This is not emphasis, because the opening Unicode nonbreaking spaces count as whitespace, too: Intraword emphasis with Rule 2: This is not emphasis, because the opening This is not emphasis, because the opening Emphasis with Here This is emphasis, even though the opening delimiter is
both left- and right-flanking, because it is preceded by
punctuation: Rule 3: This is not emphasis, because the closing delimiter does
not match the opening delimiter: This is not emphasis, because the closing A newline also counts as whitespace: This is not emphasis, because the second The point of this restriction is more easily appreciated
with this example: Intraword emphasis with Rule 4: This is not emphasis, because the closing This is not emphasis, because the second This is emphasis within emphasis: Intraword emphasis is disallowed for This is emphasis, even though the closing delimiter is
both left- and right-flanking, because it is followed by
punctuation: Rule 5: This is not strong emphasis, because the opening delimiter is
followed by whitespace: This is not strong emphasis, because the opening Intraword strong emphasis with Rule 6: This is not strong emphasis, because the opening delimiter is
followed by whitespace: A newline counts as whitespace: This is not strong emphasis, because the opening Intraword strong emphasis is forbidden with This is strong emphasis, even though the opening delimiter is
both left- and right-flanking, because it is preceded by
punctuation: Rule 7: This is not strong emphasis, because the closing delimiter is preceded
by whitespace: (Nor can it be interpreted as an emphasized This is not strong emphasis, because the second The point of this restriction is more easily appreciated
with these examples: Gomphocarpus (Gomphocarpus physocarpus, syn.
Asclepias physocarpa) Intraword emphasis: Rule 8: This is not strong emphasis, because the closing delimiter is
preceded by whitespace: This is not strong emphasis, because the second The point of this restriction is more easily appreciated
with this example: Intraword strong emphasis is forbidden with This is strong emphasis, even though the closing delimiter is
both left- and right-flanking, because it is followed by
punctuation: Rule 9: Any nonempty sequence of inline elements can be the contents of an
emphasized span. In particular, emphasis and strong emphasis can be nested
inside emphasis: Note that in the preceding case, the interpretation foobarbaz is precluded by the condition that a delimiter that
can both open and close (like the For the same reason, we don’t get two consecutive
emphasis sections in this example: The same condition ensures that the following
cases are all strong emphasis nested inside
emphasis, even when the interior spaces are
omitted: When the lengths of the interior closing and opening
delimiter runs are both multiples of 3, though,
they can match to create emphasis: Indefinite levels of nesting are possible: There can be no empty emphasis or strong emphasis: Rule 10: Any nonempty sequence of inline elements can be the contents of an
strongly emphasized span. In particular, emphasis and strong emphasis can be nested
inside strong emphasis: Indefinite levels of nesting are possible: There can be no empty emphasis or strong emphasis: Rule 11: Note that when delimiters do not match evenly, Rule 11 determines
that the excess literal Rule 12: Note that when delimiters do not match evenly, Rule 12 determines
that the excess literal Rule 13 implies that if you want emphasis nested directly inside
emphasis, you must use different delimiters: However, strong emphasis within strong emphasis is possible without
switching delimiters: Rule 13 can be applied to arbitrarily long sequences of
delimiters: Rule 14: Rule 15: Rule 16: Rule 17: GFM enables the Strikethrough text is any text wrapped in two tildes ( As with regular emphasis delimiters, a new paragraph will cause strikethrough
parsing to cease: A link contains link text (the visible text), a link destination
(the URI that is the link destination), and optionally a link title.
There are two basic kinds of links in Markdown. In inline links the
destination and title are given immediately after the link text. In
reference links the destination and title are defined elsewhere in
the document. A link text consists of a sequence of zero or more
inline elements enclosed by square brackets ( 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 Backtick code spans, autolinks, and raw HTML tags bind more tightly
than the brackets in link text. Thus, for example,
The brackets in link text bind more tightly than markers for
emphasis and strong emphasis. Thus, for example, A link destination consists of either a sequence of zero or more characters between an opening a nonempty sequence of characters that does not start with
A link title consists of either a sequence of zero or more characters between straight double-quote
characters ( a sequence of zero or more characters between straight single-quote
characters ( a sequence of zero or more characters between matching parentheses
( Although link titles may span multiple lines, they may not contain
a blank line. An inline link consists of a link text followed immediately
by a left parenthesis Here is a simple inline link: The title may be omitted: Both the title and the destination may be omitted: The destination can only contain spaces if it is
enclosed in pointy brackets: The destination cannot contain line breaks,
even if enclosed in pointy brackets: The destination can contain Pointy brackets that enclose links must be unescaped: These are not links, because the opening pointy bracket
is not matched properly: Parentheses inside the link destination may be escaped: Any number of parentheses are allowed without escaping, as long as they are
balanced: However, if you have unbalanced parentheses, you need to escape or use the
Parentheses and other symbols can also be escaped, as usual
in Markdown: A link can contain fragment identifiers and queries: Note that a backslash before a non-escapable character is
just a backslash: 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. 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: Titles may be in single quotes, double quotes, or parentheses: Backslash escapes and entity and numeric character references
may be used in titles: Titles must be separated from the link using a whitespace.
Other Unicode whitespace like non-breaking space doesn’t work. Nested balanced quotes are not allowed without escaping: But it is easy to work around this by using a different quote type: (Note: Whitespace is allowed around the destination and title: But it is not allowed between the link text and the
following parenthesis: The link text may contain balanced brackets, but not unbalanced ones,
unless they are escaped: The link text may contain inline content: However, links may not contain other links, at any level of nesting. These cases illustrate the precedence of link text grouping over
emphasis grouping: Note that brackets that aren’t part of links do not take
precedence: These cases illustrate the precedence of HTML tags, code spans,
and autolinks over link grouping: There are three kinds of reference links:
full, collapsed,
and shortcut. A full reference link
consists of a link text immediately followed by a link label
that matches a link reference definition elsewhere in the document. A link label begins with a left bracket ( One label matches
another just in case their normalized forms are equal. To normalize a
label, strip off the opening and closing brackets,
perform the Unicode case fold, strip leading and trailing
whitespace 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 link’s URI and title are provided by the matching link
reference definition. Here is a simple example: The rules for the link text are the same as with
inline links. Thus: The link text may contain balanced brackets, but not unbalanced ones,
unless they are escaped: The link text may contain inline content: However, links may not contain other links, at any level of nesting. (In the examples above, we have two shortcut reference links
instead of one full reference link.) The following cases illustrate the precedence of link text grouping over
emphasis grouping: These cases illustrate the precedence of HTML tags, code spans,
and autolinks over link grouping: [foo Matching is case-insensitive: Unicode case fold is used: Consecutive internal whitespace is treated as one space for
purposes of determining matching: No whitespace is allowed between the link text and the
link label: This is a departure from John Gruber’s original Markdown syntax
description, which explicitly allows whitespace between the link
text and the link label. It brings reference links in line with
inline links, which (according to both original Markdown and
this spec) cannot have whitespace after the link text. More
importantly, it prevents inadvertent capture of consecutive
shortcut reference links. If whitespace is allowed between the
link text and the link label, then in the following we will have
a single reference link, not two shortcut reference links, as
intended: (Note that shortcut reference links were introduced by Gruber
himself in a beta version of When there are multiple matching link reference definitions,
the first is used: 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: Link labels cannot contain brackets, unless they are
backslash-escaped: Note that in this example A link label must contain at least one non-whitespace character: A collapsed reference link
consists of a link label that matches a
link reference definition elsewhere in the
document, followed by the string The link labels are case-insensitive: As with full reference links, whitespace is not
allowed between the two sets of brackets: A shortcut reference link
consists of a link label that matches a
link reference definition elsewhere in the
document and is not followed by The link labels are case-insensitive: A space after the link text should be preserved: If you just want bracketed text, you can backslash-escape the
opening bracket to avoid links: Note that this is a link, because a link label ends with the first
following closing bracket: Full and compact references take precedence over shortcut
references: Inline links also take precedence: In the following case Here, though, Here Syntax for images is like the syntax for links, with one
difference. Instead of link text, we have an
image description. The rules for this are the
same as for link text, except that (a) an
image description starts with 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 My Reference-style: Collapsed: The labels are case-insensitive: As with reference links, whitespace is not allowed
between the two sets of brackets: Shortcut: Note that link labels cannot contain unescaped brackets: The link labels are case-insensitive: If you just want a literal If you want a link after a literal Autolinks are absolute URIs and email addresses inside
A URI autolink consists of An absolute URI,
for these purposes, consists of a scheme followed by a colon ( For purposes of this spec, a scheme is any sequence
of 2–32 characters beginning with an ASCII letter and followed
by any combination of ASCII letters, digits, or the symbols plus
(”+”), period (”.”), or hyphen (”-”). Here are some valid autolinks: Uppercase is also fine: Note that many strings that count as absolute URIs for
purposes of this spec are not valid URIs, because their
schemes are not registered or because of other problems
with their syntax: Spaces are not allowed in autolinks: Backslash-escapes do not work inside autolinks: An email autolink
consists of An email address,
for these purposes, is anything that matches
the non-normative regex from the HTML5
spec: Examples of email autolinks: Backslash-escapes do not work inside email autolinks: These are not autolinks: GFM enables the Autolinks can also be constructed without requiring the use of An extended www autolink will be recognized
when the text The scheme After a valid domain, zero or more non-space non- Visit We then apply extended autolink path validation as follows: Trailing punctuation (specifically, Visit Visit When an autolink ends in ( ( This check is only done when the link ends in a closing parentheses If an autolink ends in a semicolon ( An extended url autolink will be recognised when one of the schemes
(Visit An extended email autolink will be recognised when an email address is
recognised within any text node. Email addresses are recognised according to
the following rules: The scheme hello@mail+xyz.example isn't valid, but a.b-c_d@a.b- a.b-c_d@a.b_ Text between Here is the grammar for tags: A tag name consists of an ASCII letter
followed by zero or more ASCII letters, digits, or
hyphens ( An attribute consists of whitespace,
an attribute name, and an optional
attribute value specification. An attribute name
consists of an ASCII letter, An attribute value specification
consists of optional whitespace,
a An attribute value
consists of an unquoted attribute value,
a single-quoted attribute value, or a double-quoted attribute value. An unquoted attribute value
is a nonempty string of characters not
including whitespace, A single-quoted attribute value
consists of A double-quoted attribute value
consists of An open tag consists of a A closing tag consists of the string An HTML comment consists of A processing instruction
consists of the string A declaration consists of the
string A CDATA section consists of
the string An HTML tag consists of an open tag, a closing tag,
an HTML comment, a processing instruction, a declaration,
or a CDATA section. Here are some simple open tags: Empty elements: Whitespace is allowed: With attributes: Custom tag names can be used: Illegal tag names, not parsed as HTML: Illegal attribute names: Illegal attribute values: Illegal whitespace: Missing whitespace: Closing tags: Illegal attributes in closing tag: Comments: Not comments: Processing instructions: Declarations: CDATA sections: Entity and numeric character references are preserved in HTML
attributes: Backslash escapes do not work in HTML attributes: GFM enables the within a HTML block started by will not affect
the parser state; as the HTML block was started in by start condition 6, it
will end at any blank line. This can be surprising:
**Hello**
text remains verbatim — and regular parsing resumes, with a paragraph,
emphasised world and inline and block HTML following.
*foo*
*foo*
*foo*
*bar*
*foo*
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:
okay
import Text.HTML.TagSoup
main :: IO ()
main = print $ parseTags tags
import Text.HTML.TagSoup
main :: IO ()
main = print $ parseTags tags
matchwo(a,b)
{
if (a < b && a < 0) then {
return 1;
} else {
return 0;
}
}
]]>
okay
matchwo(a,b)
{
if (a < b && a < 0) then {
return 1;
} else {
return 0;
}
}
]]>
<div>
, ,
, , 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.
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. tags, but as described
above, raw HTML blocks starting with
can contain blank lines.
4.7Link reference definitions
:), optional whitespace (including up to one
line ending), a link destination,
optional whitespace (including up to one
line ending), and an optional link
title, which if it is present must be separated
from the link destination by whitespace.
No further non-whitespace characters may occur on the line.
[Foo*bar\]]:my_(url) 'title (with parens)'
[Foo*bar\]]
[foo]: /foo-url "foo"
[bar]: /bar-url
"bar"
[baz]: /baz-url
[foo],
[bar],
[baz]
4.8Paragraphs
4.9Blank lines
4.10Tables (extension)
table extension, where an additional leaf block type is
available.|). A leading and trailing pipe is also
recommended for clarity of reading, and if there’s otherwise parsing ambiguity.
Spaces between pipes and cell content are trimmed. Block-level elements cannot
be inserted in a table.-),
and optionally, a leading or trailing colon (:), or both, to indicate left,
right, or center alignment respectively.
| abc | defghi |
:-: | -----------:
bar | baz
is generated in HTML output:
5Container blocks
5.1Block quotes
> together
with a following space, or (b) a single character > not followed by a space.
> characters can be omitted:> characters can be indented 1-3 spaces:> before
paragraph continuation text:> cannot be omitted in the second line of> foo
> ---
> in the second line of> - foo
> - bar
> in front of
subsequent lines of an indented or fenced code block:> foo
> - bar
- bar is indented too far to start a list, and can’t
be an indented code block because indented code blocks cannot
interrupt paragraphs, so it is paragraph continuation text.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.)>s may be omitted on a continuation line of a
nested block quote:> and a following space. So five spaces are needed after
the >:
5.2List items
-, +, or * character.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.)
A paragraph
with two lines.
indented code
> A block quote.
indented code
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.
indented code
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.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:
foo is not part of the list
item:
1. A paragraph
with two lines.
indented code
> A block quote.
indented code
1. A paragraph
with two lines.
indented code
> A block quote.
indented code
1. A paragraph
with two lines.
indented code
> A block quote.
indented code
1. A paragraph
with two lines.
indented code
> A block quote.
1. A paragraph
with two lines.
indented code
> A block quote.
1. A paragraph
with two lines.
indented code
> A block quote.
indented code
5.2.1Motivation
>
delimiters need to be indented.”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.)Markdown.pl behavior, provided they are laid out
in a way that is natural for a human to read.- foo
bar
- baz
Markdown.pl parses - one
two
two a continuation paragraph:
> - one
>
> two
bar
is not indented as far as the first paragraph foo: 10. foo
bar
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:1. foo
indented code
foo.
5.3Task list items (extension)
tasklist extension, where an additional processing step is
performed on list items.[), either a whitespace character or the letter x in either
lowercase or uppercase, and then a right bracket (]). element.
- [ ] foo
- [x] bar
- [x] foo
- [ ] bar
- [x] baz
- [ ] bim
5.4Lists
-, +, or *) or (b) they are ordered list numbers with the same
delimiter (either . or )). tags, while paragraphs in a tight list are not.)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.
Markdown.pl does allow a blockquote to
interrupt a paragraph, even though the same considerations might
apply.I need to buy
- new shoes
- a coat
- a plane ticket
* I need to buy
- new shoes
- a coat
- a plane ticket
tags, since the list is “tight”),
thenI need to buy
- new shoes
- a coat
- a plane ticket
1 to
interrupt paragraphs. Thus,
The number of windows in my house is
14. The number of doors is 6.
The number of windows in my house is
1. The number of doors is 6.
- e is treated as a paragraph continuation
line, because it is indented more than three spaces:3. c is treated as in indented code block,
because it is indented four spaces and preceded by a
blank line.
6Inlines
hi is parsed as code, leaving the backtick at the end as a literal
backtick.
6.1Backslash escapes
\!\"\#\$\%\&\'\(\)\*\+\,\-\.\/\:\;\<\=\>\?\@\[\\\]\^\_\`\{\|\}\~
\*not emphasized*
\
not a tag
\[not a link](/foo)
\`not code`
1\. not a list
\* not a list
\# not a heading
\[foo]: /url "not a reference"
\ö not a character entity
6.2Entity and numeric character references
* can be used
in place of a literal * character, * cannot replace
* in emphasis delimiters, bullet list markers, or thematic
breaks.& + any of the valid
HTML5 entity names + ;. The
document https://html.spec.whatwg.org/multipage/entities.json
is used as an authoritative source for the valid entity
references and their corresponding code points.&# + a string of 1–7 arabic digits + ;. A
numeric character reference is parsed as the corresponding
Unicode character. Invalid Unicode code points will be replaced by
the REPLACEMENT CHARACTER (U+FFFD). For security reasons,
the code point U+0000 will also be replaced by U+FFFD.&# +
either X or x + a string of 1-6 hexadecimal digits + ;.
They too are parsed as the corresponding Unicode character (this
time specified with a hexadecimal numeral instead of decimal).
&x; &#; &#x;
�
&#abcdef0;
&ThisIsNotDefined; &hi?;
©), these are not
recognized here, because it makes the grammar too ambiguous:
6.3Code spans
`) that is neither
preceded nor followed by a backtick.
elements, so it is recommended that
the following CSS be used:code{white-space: pre-wrap;}
* is part of a code
span:
6.4Emphasis and strong emphasis
*) 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.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:***strong emph***
***strong** in emph*
***emph* in strong**
**in strong *emph***
*in emph **strong***
*emph *with emph* in it*
**strong **with strong** in it**
* 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.)internal emphasis: foo*bar*baz
no emphasis: foo_bar_baz
* characters that is not preceded or
followed by a non-backslash-escaped * character, or a sequence
of one or more _ characters that is not preceded or followed by
a non-backslash-escaped _ character.
***abc
_abc
**"abc"
_"abc"
abc***
abc_
"abc"**
"abc"_
abc***def
"abc"_"def"
abc *** def
a _ b
* character can open emphasis
iff (if and only if) it is part of a left-flanking delimiter run._ 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.* character can close emphasis
iff it is part of a right-flanking delimiter run._ 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.** can open strong emphasis
iff it is part of a left-flanking delimiter run.__ 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.** can close strong emphasis
iff it is part of a right-flanking delimiter run.__ can close strong emphasis iff
it is part of a right-flanking delimiter run
and either (a) not part of a left-flanking delimiter run
or (b) part of a left-flanking delimiter run
followed by punctuation._ or *) as the opening delimiter. The
opening and closing delimiters must belong to separate
delimiter runs. If one of the delimiters can both
open and close emphasis, then the sum of the lengths of the
delimiter runs containing the opening and closing delimiters
must not be a multiple of 3 unless both lengths are
multiples of 3._ or *) as the opening delimiter. The
opening and closing delimiters must belong to separate
delimiter runs. If one of the delimiters can both open
and close strong emphasis, then the sum of the lengths of
the delimiter runs containing the opening and closing
delimiters must not be a multiple of 3 unless both lengths
are multiples of 3.* character cannot occur at the beginning or end of
*-delimited emphasis or **-delimited strong emphasis, unless it
is backslash-escaped._ character cannot occur at the beginning or end of
_-delimited emphasis or __-delimited strong emphasis, unless it
is backslash-escaped.
... is always preferred to
....... is always
preferred to ....*foo _bar* baz_ is parsed as foo _bar baz_ rather
than *foo bar* baz.**foo **bar baz** is parsed as **foo bar baz
rather than foo **bar baz.*[foo*](bar) is
parsed as *foo* rather than as
[foo](bar).* is followed by
whitespace, and hence not part of a left-flanking delimiter run:* is preceded
by an alphanumeric and followed by punctuation, and hence
not part of a left-flanking delimiter run:* is permitted:_ is followed by
whitespace:_ is preceded
by an alphanumeric and followed by punctuation:_ is not allowed inside words:_ does not generate emphasis, because the first delimiter run
is right-flanking and the second left-flanking:* is preceded by
whitespace:* is
preceded by punctuation and followed by an alphanumeric
(hence it is not part of a right-flanking delimiter run:* is allowed:_ is preceded by
whitespace:_ is
preceded by punctuation and followed by an alphanumeric:_:** is preceded
by an alphanumeric and followed by punctuation, and hence
not part of a left-flanking delimiter run:** is permitted:__ is preceded
by an alphanumeric and followed by punctuation:__:*foo bar *, because of
Rule 11.)** is
preceded by punctuation and followed by an alphanumeric:
**Gomphocarpus (*Gomphocarpus physocarpus*, syn.
*Asclepias physocarpa*)**
__ is
preceded by punctuation and followed by an alphanumeric:__:* after foo)
cannot form emphasis if the sum of the lengths of
the delimiter runs containing the opening and
closing delimiters is a multiple of 3 unless
both lengths are multiples of 3.* characters will appear outside of the
emphasis, rather than inside it:_ characters will appear outside of the
emphasis, rather than inside it:
6.5Strikethrough (extension)
strikethrough extension, where an additional emphasis type is
available.~).
6.6Links
[ and ]). The
following rules apply:
[, a sequence of zero or more inlines, and
a close bracket ].[foo`]` could not be a link text, since the second ]
is part of a code span.*[foo*](url) is a link.
< and a
closing > that contains no line breaks or unescaped
< or > characters, or<, 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.
(Implementations may impose limits on parentheses nesting to
avoid performance issues, but at least three levels of nesting
should be supported.)
"), including a " character only if it is
backslash-escaped, or'), including a ' character only if it is
backslash-escaped, or(...)), including a ( or ) character only if it is
backslash-escaped.(, 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.) if it is enclosed
in pointy brackets:<...> form:
[link](#fragment)
[link](http://example.com#fragment)
[link](http://example.com?foo=3#frag)
[link](/url "title")
[link](/url 'title')
[link](/url (title))
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.)[) 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 inside the
opening and closing square brackets of link labels. A link
label can have at most 999 characters inside the square
brackets.
[foo
[foo]
[bar]
[foo]: /url1
[bar]: /url2
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.)] is not backslash-escaped:[].
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].[] 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][].[bar][baz] is parsed as a reference,
[foo] as normal text:[foo][bar] is parsed as a reference, since
[bar] is defined:[foo] is not parsed as a shortcut reference, because it
is followed by a link label (even though [bar] is not defined):
6.7Images
![ 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 *bar*]
[foo *bar*]: train.jpg "train & tracks"
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"
My 
! followed by bracketed text, you can
backslash-escape the opening [:!, backslash-escape the
!:
6.8Autolinks
< and >. They are parsed as links, with the URL or email address
as the link label.<, followed by an
absolute URI followed by >. It is parsed as
a link to the URI, with the URI as the link’s label.:)
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).
<, 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./^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?
(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/
6.9Autolinks (extension)
autolink extension, where autolinks will be recognised in a
greater number of conditions.< and to >
to delimit them, although they will be recognized under a smaller set of
circumstances. All such recognized autolinks can only come at the beginning of
a line, after whitespace, or any of the delimiting characters *, _, ~,
and (.www. is found followed by a valid domain.
A valid domain consists of segments
of alphanumeric characters, underscores (_) and hyphens (-)
separated by periods (.).
There must be at least one period,
and no underscores may be present in the last two segments of the domain.http will be inserted automatically:< characters may follow:
Visit www.commonmark.org/help for more information.
?, !, ., ,, :, *, _, and ~)
will not be considered part of the autolink, though they may be included in the
interior of the link:
Visit www.commonmark.org.
Visit www.commonmark.org/a.b.
), we scan the entire autolink for the total number
of parentheses. If there is a greater number of closing parentheses than
opening ones, we don’t consider the unmatched trailing parentheses part of the
autolink, in order to facilitate including an autolink inside a parenthesis:
www.google.com/search?q=Markup+(business)
www.google.com/search?q=Markup+(business)))
(www.google.com/search?q=Markup+(business))
(www.google.com/search?q=Markup+(business)
), so if
the only parentheses are in the interior of the autolink, no special rules are
applied:
www.google.com/search?q=(business))+ok
;), we check to see if it appears to
resemble an entity reference; if the preceding text is &
followed by one or more alphanumeric characters. If so, it is excluded from
the autolink:
www.google.com/search?q=commonmark&hl=en
www.google.com/search?q=commonmark&hl;
< immediately ends an autolink.http://, or https://, followed by a valid domain, then zero or
more non-space non-< characters according to
extended autolink path validation:
http://commonmark.org
(Visit https://encrypted.google.com/search?q=Markup+(business))
., -, _, or +.@ symbol.- or _,
separated by periods (.).
There must be at least one period.
The last character must not be one of - or _.mailto: will automatically be added to the generated link:+ can occur before the @, but not after.
hello@mail+xyz.example isn't valid, but hello+xyz@mail.example is.
., -, and _ can occur on both sides of the @, but only . may occur at
the end of the email address, in which case it will not be considered part of
the address:
a.b-c_d@a.b
a.b-c_d@a.b.
a.b-c_d@a.b-
a.b-c_d@a.b_
6.10Raw HTML
< 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.-)._, or :, followed by zero or more ASCII
letters, digits, _, ., :, or -. (Note: This is the XML
specification restricted to ASCII. HTML5 is laxer.)= character, optional whitespace, and an attribute
value.", ', =, <, >, or `.', zero or more
characters not including ', and a final '.", zero or more
characters not including ", and a final ".< character, a tag name,
zero or more attributes, optional whitespace, an optional /
character, and a > character., a
tag name, optional whitespace, and the character >.,
where text does not start with > or ->, does not end with -,
and does not contain --. (See the
HTML5 spec.), a string
of characters not including the string ?>, and the string
?>., a name consisting of one or more uppercase ASCII letters,
whitespace, a string of characters not including the
character >, and the character >., a string of characters not including the string
]]>, and the string ]]>.
6.11Disallowed Raw HTML (extension)
tagfilter extension, where the following HTML tags will be
filtered when rendering HTML output: