.commonmark.commonmark-test-util.0.7.1.source-code.spec.txt Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of commonmark-test-util Show documentation
Show all versions of commonmark-test-util Show documentation
commonmark-java classes for tests
---
title: CommonMark Spec
author: John MacFarlane
version: 0.26
date: '2016-07-15'
license: '[CC-BY-SA 4.0](http://creativecommons.org/licenses/by-sa/4.0/)'
...
# Introduction
## What is Markdown?
Markdown is a plain text format for writing structured documents,
based on conventions used for indicating formatting in email and
usenet posts. It was developed in 2004 by John Gruber, who wrote
the first Markdown-to-HTML converter in Perl, and it soon became
ubiquitous. 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.
> (` tags? Can a list be partially "loose" and partially
"tight"? What should we do with a list like this?
``` markdown
1. one
2. two
3. three
```
Or this?
``` markdown
1. one
- a
- b
2. two
```
(There are some relevant comments by John Gruber
[here](http://article.gmane.org/gmane.text.markdown.general/2554).)
5. Can list markers be indented? Can ordered list markers be right-aligned?
``` markdown
8. item 1
9. item 2
10. item 2a
```
6. Is this one list with a thematic break in its second item,
or two lists separated by a thematic break?
``` markdown
* a
* * * * *
* b
```
7. When list markers change from numbers to bullets, do we have
two lists or one? (The Markdown syntax description suggests two,
but the perl scripts and many other implementations produce one.)
``` markdown
1. fee
2. fie
- foe
- fum
```
8. What are the precedence rules for the markers of inline structure?
For example, is the following a valid link, or does the code span
take precedence ?
``` markdown
[a backtick (`)](/url) and [another backtick (`)](/url).
```
9. What are the precedence rules for markers of emphasis and strong
emphasis? For example, how should the following be parsed?
``` markdown
*foo *bar* baz*
```
10. What are the precedence rules between block-level and inline-level
structure? For example, how should the following be parsed?
``` markdown
- `a long code span can contain a hyphen like this
- and it can screw things up`
```
11. Can list items include section headings? (`Markdown.pl` does not
allow this, but does allow blockquotes to include headings.)
``` markdown
- # Heading
```
12. Can list items be empty?
``` markdown
* a
*
* b
```
13. Can link references be defined inside block quotes or list items?
``` markdown
> Blockquote [foo].
>
> [foo]: /url
```
14. If there are multiple definitions for the same reference, which takes
precedence?
``` markdown
[foo]: /url1
[foo]: /url2
[foo][]
```
In the absence of a spec, early implementers consulted `Markdown.pl`
to resolve these ambiguities. But `Markdown.pl` was quite buggy, and
gave manifestly bad results in many cases, so it was not a
satisfactory replacement for a spec.
Because there is no unambiguous spec, implementations have diverged
considerably. As a result, users are often surprised to find that
a document that renders one way on one system (say, a github wiki)
renders differently on another (say, converting to docbook using
pandoc). To make matters worse, because nothing in Markdown counts
as a "syntax error," the divergence often isn't discovered right away.
## About this document
This document attempts to specify Markdown syntax unambiguously.
It contains many examples with side-by-side Markdown and
HTML. These are intended to double as conformance tests. An
accompanying script `spec_tests.py` can be used to run the tests
against any Markdown program:
python test/spec_tests.py --spec spec.txt --program PROGRAM
Since this document describes how Markdown is to be parsed into
an abstract syntax tree, it would have made sense to use an abstract
representation of the syntax tree instead of HTML. But HTML is capable
of representing the structural distinctions we need to make, and the
choice of HTML for the tests makes it possible to run the tests against
an implementation without writing an abstract syntax tree renderer.
This document is generated from a text file, `spec.txt`, written
in Markdown with a small extension for the side-by-side tests.
The script `tools/makespec.py` can be used to convert `spec.txt` into
HTML or CommonMark (which can then be converted into other formats).
In the examples, the `→` character is used to represent tabs.
# Preliminaries
## Characters and lines
Any sequence of [characters] is a valid CommonMark
document.
A [character](@) is a Unicode code point. Although some
code points (for example, combining accents) do not correspond to
characters in an intuitive sense, all code points count as characters
for purposes of this spec.
This spec does not specify an encoding; it thinks of lines as composed
of [characters] rather than bytes. A conforming parser may be limited
to a certain encoding.
A [line](@) is a sequence of zero or more [characters]
other than newline (`U+000A`) or carriage return (`U+000D`),
followed by a [line ending] or by the end of file.
A [line ending](@) is a newline (`U+000A`), a carriage return
(`U+000D`) not followed by a newline, or a carriage return and a
following newline.
A line containing no characters, or a line containing only spaces
(`U+0020`) or tabs (`U+0009`), is called a [blank line](@).
The following definitions of character classes will be used in this spec:
A [whitespace character](@) is a space
(`U+0020`), tab (`U+0009`), newline (`U+000A`), line tabulation (`U+000B`),
form feed (`U+000C`), or carriage return (`U+000D`).
[Whitespace](@) is a sequence of one or more [whitespace
characters].
A [Unicode whitespace character](@) is
any code point in the Unicode `Zs` class, or a tab (`U+0009`),
carriage return (`U+000D`), newline (`U+000A`), or form feed
(`U+000C`).
[Unicode whitespace](@) is a sequence of one
or more [Unicode whitespace characters].
A [space](@) is `U+0020`.
A [non-whitespace character](@) is any character
that is not a [whitespace character].
An [ASCII punctuation character](@)
is `!`, `"`, `#`, `$`, `%`, `&`, `'`, `(`, `)`,
`*`, `+`, `,`, `-`, `.`, `/`, `:`, `;`, `<`, `=`, `>`, `?`, `@`,
`[`, `\`, `]`, `^`, `_`, `` ` ``, `{`, `|`, `}`, or `~`.
A [punctuation character](@) is an [ASCII
punctuation character] or anything in
the Unicode classes `Pc`, `Pd`, `Pe`, `Pf`, `Pi`, `Po`, or `Ps`.
## Tabs
Tabs in lines are not expanded to [spaces]. However,
in contexts where whitespace helps to define block structure,
tabs behave as if they were replaced by spaces with a tab stop
of 4 characters.
Thus, for example, a tab can be used instead of four spaces
in an indented code block. (Note, however, that internal
tabs are passed through as literal tabs, not expanded to
spaces.)
```````````````````````````````` example
→foo→baz→→bim
.
foo→baz→→bim
````````````````````````````````
```````````````````````````````` example
→foo→baz→→bim
.
foo→baz→→bim
````````````````````````````````
```````````````````````````````` example
a→a
ὐ→a
.
a→a
ὐ→a
````````````````````````````````
In the following example, a continuation paragraph of a list
item is indented with a tab; this has exactly the same effect
as indentation with four spaces would:
```````````````````````````````` example
- foo
→bar
.
-
foo
bar
````````````````````````````````
```````````````````````````````` example
- foo
→→bar
.
-
foo
bar
````````````````````````````````
Normally the `>` that begins a block quote may be followed
optionally by a space, which is not considered part of the
content. In the following case `>` is followed by a tab,
which is treated as if it were expanded into spaces.
Since one of theses spaces is considered part of the
delimiter, `foo` is considered to be indented six spaces
inside the block quote context, so we get an indented
code block starting with two spaces.
```````````````````````````````` example
>→→foo
.
foo
````````````````````````````````
```````````````````````````````` example
-→→foo
.
-
foo
````````````````````````````````
```````````````````````````````` example
foo
→bar
.
foo
bar
````````````````````````````````
```````````````````````````````` example
- foo
- bar
→ - baz
.
- foo
- bar
- baz
````````````````````````````````
```````````````````````````````` example
#→Foo
.
Foo
````````````````````````````````
```````````````````````````````` example
*→*→*→
.
````````````````````````````````
## Insecure characters
For security reasons, the Unicode character `U+0000` must be replaced
with the REPLACEMENT CHARACTER (`U+FFFD`).
# Blocks and inlines
We can think of a document as a sequence of
[blocks](@)---structural elements like paragraphs, block
quotations, lists, headings, rules, and code blocks. Some blocks (like
block quotes and list items) contain other blocks; others (like
headings and paragraphs) contain [inline](@) content---text,
links, emphasized text, images, code, and so on.
## Precedence
Indicators of block structure always take precedence over indicators
of inline structure. So, for example, the following is a list with
two items, not a list with one item containing a code span:
```````````````````````````````` example
- `one
- two`
.
- `one
- two`
````````````````````````````````
This means that parsing can proceed in two steps: first, the block
structure of the document can be discerned; second, text lines inside
paragraphs, headings, and other block constructs can be parsed for inline
structure. The second step requires information about link reference
definitions that will be available only at the end of the first
step. Note that the first step requires processing lines in sequence,
but the second can be parallelized, since the inline parsing of
one block element does not affect the inline parsing of any other.
## Container blocks and leaf blocks
We can divide blocks into two types:
[container block](@)s,
which can contain other blocks, and [leaf block](@)s,
which cannot.
# Leaf blocks
This section describes the different kinds of leaf block that make up a
Markdown document.
## Thematic breaks
A line consisting of 0-3 spaces of indentation, followed by a sequence
of three or more matching `-`, `_`, or `*` characters, each followed
optionally by any number of spaces, forms a
[thematic break](@).
```````````````````````````````` example
***
---
___
.
````````````````````````````````
Wrong characters:
```````````````````````````````` example
+++
.
+++
````````````````````````````````
```````````````````````````````` example
===
.
===
````````````````````````````````
Not enough characters:
```````````````````````````````` example
--
**
__
.
--
**
__
````````````````````````````````
One to three spaces indent are allowed:
```````````````````````````````` example
***
***
***
.
````````````````````````````````
Four spaces is too many:
```````````````````````````````` example
***
.
***
````````````````````````````````
```````````````````````````````` example
Foo
***
.
Foo
***
````````````````````````````````
More than three characters may be used:
```````````````````````````````` example
_____________________________________
.
````````````````````````````````
Spaces are allowed between the characters:
```````````````````````````````` example
- - -
.
````````````````````````````````
```````````````````````````````` example
** * ** * ** * **
.
````````````````````````````````
```````````````````````````````` example
- - - -
.
````````````````````````````````
Spaces are allowed at the end:
```````````````````````````````` example
- - - -
.
````````````````````````````````
However, no other characters may occur in the line:
```````````````````````````````` example
_ _ _ _ a
a------
---a---
.
_ _ _ _ a
a------
---a---
````````````````````````````````
It is required that all of the [non-whitespace characters] be the same.
So, this is not a thematic break:
```````````````````````````````` example
*-*
.
-
````````````````````````````````
Thematic breaks do not need blank lines before or after:
```````````````````````````````` example
- foo
***
- bar
.
- foo
- bar
````````````````````````````````
Thematic breaks can interrupt a paragraph:
```````````````````````````````` example
Foo
***
bar
.
Foo
bar
````````````````````````````````
If a line of dashes that meets the above conditions for being a
thematic break could also be interpreted as the underline of a [setext
heading], the interpretation as a
[setext heading] takes precedence. Thus, for example,
this is a setext heading, not a paragraph followed by a thematic break:
```````````````````````````````` example
Foo
---
bar
.
Foo
bar
````````````````````````````````
When both a thematic break and a list item are possible
interpretations of a line, the thematic break takes precedence:
```````````````````````````````` example
* Foo
* * *
* Bar
.
- Foo
- Bar
````````````````````````````````
If you want a thematic break in a list item, use a different bullet:
```````````````````````````````` example
- Foo
- * * *
.
- Foo
-
````````````````````````````````
## ATX headings
An [ATX heading](@)
consists of a string of characters, parsed as inline content, between an
opening sequence of 1--6 unescaped `#` characters and an optional
closing sequence of any number of unescaped `#` characters.
The opening sequence of `#` characters must be followed by a
[space] or by the end of line. The optional closing sequence of `#`s must be
preceded by a [space] and may be followed by spaces only. The opening
`#` character may be indented 0-3 spaces. The raw contents of the
heading are stripped of leading and trailing spaces before being parsed
as inline content. The heading level is equal to the number of `#`
characters in the opening sequence.
Simple headings:
```````````````````````````````` example
# foo
## foo
### foo
#### foo
##### foo
###### foo
.
foo
foo
foo
foo
foo
foo
````````````````````````````````
More than six `#` characters is not a heading:
```````````````````````````````` example
####### foo
.
####### foo
````````````````````````````````
At least one space is required between the `#` characters and the
heading's contents, unless the heading is empty. Note that many
implementations currently do not require the space. However, the
space was required by the
[original ATX implementation](http://www.aaronsw.com/2002/atx/atx.py),
and it helps prevent things like the following from being parsed as
headings:
```````````````````````````````` example
#5 bolt
#hashtag
.
#5 bolt
#hashtag
````````````````````````````````
This is not a heading, because the first `#` is escaped:
```````````````````````````````` example
\## foo
.
## foo
````````````````````````````````
Contents are parsed as inlines:
```````````````````````````````` example
# foo *bar* \*baz\*
.
foo bar *baz*
````````````````````````````````
Leading and trailing blanks are ignored in parsing inline content:
```````````````````````````````` example
# foo
.
foo
````````````````````````````````
One to three spaces indentation are allowed:
```````````````````````````````` example
### foo
## foo
# foo
.
foo
foo
foo
````````````````````````````````
Four spaces are too much:
```````````````````````````````` example
# foo
.
# foo
````````````````````````````````
```````````````````````````````` example
foo
# bar
.
foo
# bar
````````````````````````````````
A closing sequence of `#` characters is optional:
```````````````````````````````` example
## foo ##
### bar ###
.
foo
bar
````````````````````````````````
It need not be the same length as the opening sequence:
```````````````````````````````` example
# foo ##################################
##### foo ##
.
foo
foo
````````````````````````````````
Spaces are allowed after the closing sequence:
```````````````````````````````` example
### foo ###
.
foo
````````````````````````````````
A sequence of `#` characters with anything but [spaces] following it
is not a closing sequence, but counts as part of the contents of the
heading:
```````````````````````````````` example
### foo ### b
.
foo ### b
````````````````````````````````
The closing sequence must be preceded by a space:
```````````````````````````````` example
# foo#
.
foo#
````````````````````````````````
Backslash-escaped `#` characters do not count as part
of the closing sequence:
```````````````````````````````` example
### foo \###
## foo #\##
# foo \#
.
foo ###
foo ###
foo #
````````````````````````````````
ATX headings need not be separated from surrounding content by blank
lines, and they can interrupt paragraphs:
```````````````````````````````` example
****
## foo
****
.
foo
````````````````````````````````
```````````````````````````````` example
Foo bar
# baz
Bar foo
.
Foo bar
baz
Bar foo
````````````````````````````````
ATX headings can be empty:
```````````````````````````````` example
##
#
### ###
.
````````````````````````````````
## Setext headings
A [setext heading](@) consists of one or more
lines of text, each containing at least one [non-whitespace
character], with no more than 3 spaces indentation, followed by
a [setext heading underline]. The lines of text must be such
that, were they not followed by the setext heading underline,
they would be interpreted as a paragraph: they cannot be
interpretable as a [code fence], [ATX heading][ATX headings],
[block quote][block quotes], [thematic break][thematic breaks],
[list item][list items], or [HTML block][HTML blocks].
A [setext heading underline](@) is a sequence of
`=` characters or a sequence of `-` characters, with no more than 3
spaces indentation and any number of trailing spaces. If a line
containing a single `-` can be interpreted as an
empty [list items], it should be interpreted this way
and not as a [setext heading underline].
The heading is a level 1 heading if `=` characters are used in
the [setext heading underline], and a level 2 heading if `-`
characters are used. The contents of the heading are the result
of parsing the preceding lines of text as CommonMark inline
content.
In general, a setext heading need not be preceded or followed by a
blank line. However, it cannot interrupt a paragraph, so when a
setext heading comes after a paragraph, a blank line is needed between
them.
Simple examples:
```````````````````````````````` example
Foo *bar*
=========
Foo *bar*
---------
.
Foo bar
Foo bar
````````````````````````````````
The content of the header may span more than one line:
```````````````````````````````` example
Foo *bar
baz*
====
.
Foo bar
baz
````````````````````````````````
The underlining can be any length:
```````````````````````````````` example
Foo
-------------------------
Foo
=
.
Foo
Foo
````````````````````````````````
The heading content can be indented up to three spaces, and need
not line up with the underlining:
```````````````````````````````` example
Foo
---
Foo
-----
Foo
===
.
Foo
Foo
Foo
````````````````````````````````
Four spaces indent is too much:
```````````````````````````````` example
Foo
---
Foo
---
.
Foo
---
Foo
````````````````````````````````
The setext heading underline can be indented up to three spaces, and
may have trailing spaces:
```````````````````````````````` example
Foo
----
.
Foo
````````````````````````````````
Four spaces is too much:
```````````````````````````````` example
Foo
---
.
Foo
---
````````````````````````````````
The setext heading underline cannot contain internal spaces:
```````````````````````````````` example
Foo
= =
Foo
--- -
.
Foo
= =
Foo
````````````````````````````````
Trailing spaces in the content line do not cause a line break:
```````````````````````````````` example
Foo
-----
.
Foo
````````````````````````````````
Nor does a backslash at the end:
```````````````````````````````` example
Foo\
----
.
Foo\
````````````````````````````````
Since indicators of block structure take precedence over
indicators of inline structure, the following are setext headings:
```````````````````````````````` example
`Foo
----
`
.
`Foo
`
<a title="a lot
of dashes"/>
````````````````````````````````
The setext heading underline cannot be a [lazy continuation
line] in a list item or block quote:
```````````````````````````````` example
> Foo
---
.
Foo
````````````````````````````````
```````````````````````````````` example
> foo
bar
===
.
foo
bar
===
````````````````````````````````
```````````````````````````````` example
- Foo
---
.
- Foo
````````````````````````````````
A blank line is needed between a paragraph and a following
setext heading, since otherwise the paragraph becomes part
of the heading's content:
```````````````````````````````` example
Foo
Bar
---
.
Foo
Bar
````````````````````````````````
But in general a blank line is not required before or after
setext headings:
```````````````````````````````` example
---
Foo
---
Bar
---
Baz
.
Foo
Bar
Baz
````````````````````````````````
Setext headings cannot be empty:
```````````````````````````````` example
====
.
====
````````````````````````````````
Setext heading text lines must not be interpretable as block
constructs other than paragraphs. So, the line of dashes
in these examples gets interpreted as a thematic break:
```````````````````````````````` example
---
---
.
````````````````````````````````
```````````````````````````````` example
- foo
-----
.
- foo
````````````````````````````````
```````````````````````````````` example
foo
---
.
foo
````````````````````````````````
```````````````````````````````` example
> foo
-----
.
foo
````````````````````````````````
If you want a heading with `> foo` as its literal text, you can
use backslash escapes:
```````````````````````````````` example
\> foo
------
.
> foo
````````````````````````````````
**Compatibility note:** Most existing Markdown implementations
do not allow the text of setext headings to span multiple lines.
But there is no consensus about how to interpret
``` markdown
Foo
bar
---
baz
```
One can find four different interpretations:
1. paragraph "Foo", heading "bar", paragraph "baz"
2. paragraph "Foo bar", thematic break, paragraph "baz"
3. paragraph "Foo bar --- baz"
4. heading "Foo bar", paragraph "baz"
We find interpretation 4 most natural, and interpretation 4
increases the expressive power of CommonMark, by allowing
multiline headings. Authors who want interpretation 1 can
put a blank line after the first paragraph:
```````````````````````````````` example
Foo
bar
---
baz
.
Foo
bar
baz
````````````````````````````````
Authors who want interpretation 2 can put blank lines around
the thematic break,
```````````````````````````````` example
Foo
bar
---
baz
.
Foo
bar
baz
````````````````````````````````
or use a thematic break that cannot count as a [setext heading
underline], such as
```````````````````````````````` example
Foo
bar
* * *
baz
.
Foo
bar
baz
````````````````````````````````
Authors who want interpretation 3 can use backslash escapes:
```````````````````````````````` example
Foo
bar
\---
baz
.
Foo
bar
---
baz
````````````````````````````````
## Indented code blocks
An [indented code block](@) is composed of one or more
[indented chunks] separated by blank lines.
An [indented chunk](@) is a sequence of non-blank lines,
each indented four or more spaces. The contents of the code block are
the literal contents of the lines, including trailing
[line endings], minus four spaces of indentation.
An indented code block has no [info string].
An indented code block cannot interrupt a paragraph, so there must be
a blank line between a paragraph and a following indented code block.
(A blank line is not needed, however, between a code block and a following
paragraph.)
```````````````````````````````` example
a simple
indented code block
.
a simple
indented code block
````````````````````````````````
If there is any ambiguity between an interpretation of indentation
as a code block and as indicating that material belongs to a [list
item][list items], the list item interpretation takes precedence:
```````````````````````````````` example
- foo
bar
.
-
foo
bar
````````````````````````````````
```````````````````````````````` example
1. foo
- bar
.
-
foo
- bar
````````````````````````````````
The contents of a code block are literal text, and do not get parsed
as Markdown:
```````````````````````````````` example
*hi*
- one
.
<a/>
*hi*
- one
````````````````````````````````
Here we have three chunks separated by blank lines:
```````````````````````````````` example
chunk1
chunk2
chunk3
.
chunk1
chunk2
chunk3
````````````````````````````````
Any initial spaces beyond four will be included in the content, even
in interior blank lines:
```````````````````````````````` example
chunk1
chunk2
.
chunk1
chunk2
````````````````````````````````
An indented code block cannot interrupt a paragraph. (This
allows hanging indents and the like.)
```````````````````````````````` example
Foo
bar
.
Foo
bar
````````````````````````````````
However, any non-blank line with fewer than four leading spaces ends
the code block immediately. So a paragraph may occur immediately
after indented code:
```````````````````````````````` example
foo
bar
.
foo
bar
````````````````````````````````
And indented code can occur immediately before and after other kinds of
blocks:
```````````````````````````````` example
# Heading
foo
Heading
------
foo
----
.
Heading
foo
Heading
foo
````````````````````````````````
The first line can be indented more than four spaces:
```````````````````````````````` example
foo
bar
.
foo
bar
````````````````````````````````
Blank lines preceding or following an indented code block
are not included in it:
```````````````````````````````` example
foo
.
foo
````````````````````````````````
Trailing spaces are included in the code block's content:
```````````````````````````````` example
foo
.
foo
````````````````````````````````
## Fenced code blocks
A [code fence](@) is a sequence
of at least three consecutive backtick characters (`` ` ``) or
tildes (`~`). (Tildes and backticks cannot be mixed.)
A [fenced code block](@)
begins with a code fence, indented no more than three spaces.
The line with the opening code fence may optionally contain some text
following the code fence; this is trimmed of leading and trailing
spaces and called the [info string](@).
The [info string] may not contain any backtick
characters. (The reason for this restriction is that otherwise
some inline code would be incorrectly interpreted as the
beginning of a fenced code block.)
The content of the code block consists of all subsequent lines, until
a closing [code fence] of the same type as the code block
began with (backticks or tildes), and with at least as many backticks
or tildes as the opening code fence. If the leading code fence is
indented N spaces, then up to N spaces of indentation are removed from
each line of the content (if present). (If a content line is not
indented, it is preserved unchanged. If it is indented less than N
spaces, all of the indentation is removed.)
The closing code fence may be indented up to three spaces, and may be
followed only by spaces, which are ignored. If the end of the
containing block (or document) is reached and no closing code fence
has been found, the code block contains all of the lines after the
opening code fence until the end of the containing block (or
document). (An alternative spec would require backtracking in the
event that a closing code fence is not found. But this makes parsing
much less efficient, and there seems to be no real down side to the
behavior described here.)
A fenced code block may interrupt a paragraph, and does not require
a blank line either before or after.
The content of a code fence is treated as literal text, not parsed
as inlines. The first word of the [info string] is typically used to
specify the language of the code sample, and rendered in the `class`
attribute of the `code` tag. However, this spec does not mandate any
particular treatment of the [info string].
Here is a simple example with backticks:
```````````````````````````````` example
```
<
>
```
.
<
>
````````````````````````````````
With tildes:
```````````````````````````````` example
~~~
<
>
~~~
.
<
>
````````````````````````````````
The closing code fence must use the same character as the opening
fence:
```````````````````````````````` example
```
aaa
~~~
```
.
aaa
~~~
````````````````````````````````
```````````````````````````````` example
~~~
aaa
```
~~~
.
aaa
```
````````````````````````````````
The closing code fence must be at least as long as the opening fence:
```````````````````````````````` example
````
aaa
```
``````
.
aaa
```
````````````````````````````````
```````````````````````````````` example
~~~~
aaa
~~~
~~~~
.
aaa
~~~
````````````````````````````````
Unclosed code blocks are closed by the end of the document
(or the enclosing [block quote][block quotes] or [list item][list items]):
```````````````````````````````` example
```
.
````````````````````````````````
```````````````````````````````` example
`````
```
aaa
.
```
aaa
````````````````````````````````
```````````````````````````````` example
> ```
> aaa
bbb
.
aaa
bbb
````````````````````````````````
A code block can have all empty lines as its content:
```````````````````````````````` example
```
```
.
````````````````````````````````
A code block can be empty:
```````````````````````````````` example
```
```
.
````````````````````````````````
Fences can be indented. If the opening fence is indented,
content lines will have equivalent opening indentation removed,
if present:
```````````````````````````````` example
```
aaa
aaa
```
.
aaa
aaa
````````````````````````````````
```````````````````````````````` example
```
aaa
aaa
aaa
```
.
aaa
aaa
aaa
````````````````````````````````
```````````````````````````````` example
```
aaa
aaa
aaa
```
.
aaa
aaa
aaa
````````````````````````````````
Four spaces indentation produces an indented code block:
```````````````````````````````` example
```
aaa
```
.
```
aaa
```
````````````````````````````````
Closing fences may be indented by 0-3 spaces, and their indentation
need not match that of the opening fence:
```````````````````````````````` example
```
aaa
```
.
aaa
````````````````````````````````
```````````````````````````````` example
```
aaa
```
.
aaa
````````````````````````````````
This is not a closing fence, because it is indented 4 spaces:
```````````````````````````````` example
```
aaa
```
.
aaa
```
````````````````````````````````
Code fences (opening and closing) cannot contain internal spaces:
```````````````````````````````` example
``` ```
aaa
.
````````````````````````````````
```````````````````````````````` example
~~~~~~
aaa
~~~ ~~
.
aaa
~~~ ~~
````````````````````````````````
Fenced code blocks can interrupt paragraphs, and can be followed
directly by paragraphs, without a blank line between:
```````````````````````````````` example
foo
```
bar
```
baz
.
foo
bar
baz
````````````````````````````````
Other blocks can also occur before and after fenced code blocks
without an intervening blank line:
```````````````````````````````` example
foo
---
~~~
bar
~~~
# baz
.
foo
bar
baz
````````````````````````````````
An [info string] can be provided after the opening code fence.
Opening and closing spaces will be stripped, and the first word, prefixed
with `language-`, is used as the value for the `class` attribute of the
`code` element within the enclosing `pre` element.
```````````````````````````````` example
```ruby
def foo(x)
return 3
end
```
.
def foo(x)
return 3
end
````````````````````````````````
```````````````````````````````` example
~~~~ ruby startline=3 $%@#$
def foo(x)
return 3
end
~~~~~~~
.
def foo(x)
return 3
end
````````````````````````````````
```````````````````````````````` example
````;
````
.
````````````````````````````````
[Info strings] for backtick code blocks cannot contain backticks:
```````````````````````````````` example
``` aa ```
foo
.
aa
foo
````````````````````````````````
Closing code fences cannot have [info strings]:
```````````````````````````````` example
```
``` aaa
```
.
``` aaa
````````````````````````````````
## HTML blocks
An [HTML block](@) is a group of lines that is treated
as raw HTML (and will not be escaped in HTML output).
There are seven kinds of [HTML block], which can be defined
by their start and end conditions. The block begins with a line that
meets a [start condition](@) (after up to three spaces
optional indentation). It ends with the first subsequent line that
meets a matching [end condition](@), or the last line of
the document or other [container block](@), if no line is encountered that meets the
[end condition]. If the first line meets both the [start condition]
and the [end condition], the block will contain just that line.
1. **Start condition:** line begins with the string ``, or the end of the line.\
**End condition:** line contains an end tag
``, ` | hi |
| hi |
okay.
```````````````````````````````` ```````````````````````````````` example
*hello*
.
*foo*
.
*foo*
````````````````````````````````
Here we have two HTML blocks with a Markdown paragraph between them:
```````````````````````````````` example
*Markdown*
.
Markdown
*foo*
*bar*
.
*foo*
.
````````````````````````````````
Everything until the next blank line or end of document
gets included in the HTML block. So, in the following
example, what looks like a Markdown code block
is actually part of the HTML block, which continues until a blank
line or the end of the document is reached:
```````````````````````````````` example
``` c
int x = 33;
```
.
``` c
int x = 33;
```
````````````````````````````````
To start an [HTML block] with a tag that is *not* in the
list of block-level tags in (6), you must put the tag by
itself on the first line (and it must be complete):
```````````````````````````````` example
*bar*
.
*bar*
````````````````````````````````
In type 7 blocks, the [tag name] can be anything:
```````````````````````````````` example
*bar*
.
*bar*
````````````````````````````````
```````````````````````````````` example
*bar*
.
*bar*
````````````````````````````````
```````````````````````````````` example
*bar*
.
*bar*
````````````````````````````````
These rules are designed to allow us to work with tags that
can function as either block-level or inline-level tags.
The `` tag is a nice example. We can surround content with
`` tags in three different ways. In this case, we get a raw
HTML block, because the `` tag is on a line by itself:
```````````````````````````````` example
*foo*
.
*foo*
````````````````````````````````
In this case, we get a raw HTML block that just includes
the `` tag (because it ends with the following blank
line). So the contents get interpreted as CommonMark:
```````````````````````````````` example
*foo*
.
````````````````````````````````
Finally, in this case, the `` tags are interpreted
as [raw HTML] *inside* the CommonMark paragraph. (Because
the tag is not on a line by itself, we get inline HTML
rather than an [HTML block].)
```````````````````````````````` example
*foo*
.
bar
```````````````````````````````` A partial tag need not even be completed (garbage in, garbage out): ```````````````````````````````` example . ```````````````````````````````` ```````````````````````````````` example| foo |
| foo |
foo
foo
import Text.HTML.TagSoup
main :: IO ()
main = print $ parseTags tags
import Text.HTML.TagSoup
main :: IO ()
main = print $ parseTags tags
okay
```````````````````````````````` A script tag (type 1): ```````````````````````````````` example okay .okay
```````````````````````````````` A style tag (type 1): ```````````````````````````````` example okay .okay
```````````````````````````````` If there is no matching end tag, the block will end at the end of the document (or the enclosing [block quote][block quotes] or [list item][list items]): ```````````````````````````````` example *foo* .foo
```````````````````````````````` ```````````````````````````````` example *bar* *baz* . *bar*baz
```````````````````````````````` Note that anything on the last line after the end tag will be included in the [HTML block]: ```````````````````````````````` example 1. *bar* . 1. *bar* ```````````````````````````````` A comment (type 2): ```````````````````````````````` example okay .okay
```````````````````````````````` A processing instruction (type 3): ```````````````````````````````` example '; ?> okay . '; ?>okay
```````````````````````````````` A declaration (type 4): ```````````````````````````````` example . ```````````````````````````````` CDATA (type 5): ```````````````````````````````` example okay .okay
```````````````````````````````` The opening tag can be indented 1-3 spaces, but not 4: ```````````````````````````````` example .<!-- foo -->
.
<div>
bar
.
Foo
bar
````````````````````````````````
However, a following blank line is needed, except at the end of
a document, and except for blocks of types 1--5, above:
```````````````````````````````` example
bar
*foo*
.
bar
*foo*
````````````````````````````````
HTML blocks of type 7 cannot interrupt a paragraph:
```````````````````````````````` example
Foo
baz
.
Foo baz
```````````````````````````````` This rule differs from John Gruber's original Markdown syntax specification, which says: > The only restrictions are that block-level HTML elements — > e.g. ``, `
