` within a HTML block started by `
` tags? Can a list be partially "loose" and partially "tight"? What should we do with a list like this? ``` markdown 1. one 2. two 3. three ``` Or this? ``` markdown 1. one - a - b 2. two ``` (There are some relevant comments by John Gruber [here](http://article.gmane.org/gmane.text.markdown.general/2554).) 5. Can list markers be indented? Can ordered list markers be right-aligned? ``` markdown 8. item 1 9. item 2 10. item 2a ``` 6. Is this one list with a thematic break in its second item, or two lists separated by a thematic break? ``` markdown * a * * * * * * b ``` 7. When list markers change from numbers to bullets, do we have two lists or one? (The Markdown syntax description suggests two, but the perl scripts and many other implementations produce one.) ``` markdown 1. fee 2. fie - foe - fum ``` 8. What are the precedence rules for the markers of inline structure? For example, is the following a valid link, or does the code span take precedence ? ``` markdown [a backtick (`)](/url) and [another backtick (`)](/url). ``` 9. What are the precedence rules for markers of emphasis and strong emphasis? For example, how should the following be parsed? ``` markdown *foo *bar* baz* ``` 10. What are the precedence rules between block-level and inline-level structure? For example, how should the following be parsed? ``` markdown - `a long code span can contain a hyphen like this - and it can screw things up` ``` 11. Can list items include section headings? (`Markdown.pl` does not allow this, but does allow blockquotes to include headings.) ``` markdown - # Heading ``` 12. Can list items be empty? ``` markdown * a * * b ``` 13. Can link references be defined inside block quotes or list items? ``` markdown > Blockquote [foo]. > > [foo]: /url ``` 14. If there are multiple definitions for the same reference, which takes precedence? ``` markdown [foo]: /url1 [foo]: /url2 [foo][] ``` In the absence of a spec, early implementers consulted `Markdown.pl` to resolve these ambiguities. But `Markdown.pl` was quite buggy, and gave manifestly bad results in many cases, so it was not a satisfactory replacement for a spec. Because there is no unambiguous spec, implementations have diverged considerably. As a result, users are often surprised to find that a document that renders one way on one system (say, a GitHub wiki) renders differently on another (say, converting to docbook using pandoc). To make matters worse, because nothing in Markdown counts as a "syntax error," the divergence often isn't discovered right away. ## About this document This document attempts to specify Markdown syntax unambiguously. It contains many examples with side-by-side Markdown and HTML. These are intended to double as conformance tests. An accompanying script `spec_tests.py` can be used to run the tests against any Markdown program: python test/spec_tests.py --spec spec.txt --program PROGRAM Since this document describes how Markdown is to be parsed into an abstract syntax tree, it would have made sense to use an abstract representation of the syntax tree instead of HTML. But HTML is capable of representing the structural distinctions we need to make, and the choice of HTML for the tests makes it possible to run the tests against an implementation without writing an abstract syntax tree renderer. This document is generated from a text file, `spec.txt`, written in Markdown with a small extension for the side-by-side tests. The script `tools/makespec.py` can be used to convert `spec.txt` into HTML or CommonMark (which can then be converted into other formats). In the examples, the `→` character is used to represent tabs. # Preliminaries ## Characters and lines Any sequence of [characters] is a valid CommonMark document. A [character](@) is a Unicode code point. Although some code points (for example, combining accents) do not correspond to characters in an intuitive sense, all code points count as characters for purposes of this spec. This spec does not specify an encoding; it thinks of lines as composed of [characters] rather than bytes. A conforming parser may be limited to a certain encoding. A [line](@) is a sequence of zero or more [characters] other than newline (`U+000A`) or carriage return (`U+000D`), followed by a [line ending] or by the end of file. A [line ending](@) is a newline (`U+000A`), a carriage return (`U+000D`) not followed by a newline, or a carriage return and a following newline. A line containing no characters, or a line containing only spaces (`U+0020`) or tabs (`U+0009`), is called a [blank line](@). The following definitions of character classes will be used in this spec: A [whitespace character](@) is a space (`U+0020`), tab (`U+0009`), newline (`U+000A`), line tabulation (`U+000B`), form feed (`U+000C`), or carriage return (`U+000D`). [Whitespace](@) is a sequence of one or more [whitespace characters]. A [Unicode whitespace character](@) is any code point in the Unicode `Zs` general category, or a tab (`U+0009`), carriage return (`U+000D`), newline (`U+000A`), or form feed (`U+000C`). [Unicode whitespace](@) is a sequence of one or more [Unicode whitespace characters]. A [space](@) is `U+0020`. A [non-whitespace character](@) is any character that is not a [whitespace character]. An [ASCII punctuation character](@) is `!`, `"`, `#`, `$`, `%`, `&`, `'`, `(`, `)`, `*`, `+`, `,`, `-`, `.`, `/` (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 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
foo baz bim
a a
ὐ a
foo
bar
foo
bar
```````````````````````````````` ```````````````````````````````` example - foo .foo
foo
foo
bar
+++
```````````````````````````````` ```````````````````````````````` example === .===
```````````````````````````````` Not enough characters: ```````````````````````````````` example -- ** __ .-- ** __
```````````````````````````````` One to three spaces indent are allowed: ```````````````````````````````` example *** *** *** .***
Foo ***
```````````````````````````````` More than three characters may be used: ```````````````````````````````` example _____________________________________ ._ _ _ _ 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
```````````````````````````````` 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 .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
```````````````````````````````` 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
foo # bar
```````````````````````````````` A closing sequence of `#` characters is optional: ```````````````````````````````` example ## foo ## ### bar ### .Foo bar
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
---
Foo
Foo ---
```````````````````````````````` The setext heading underline cannot contain internal spaces: ```````````````````````````````` example Foo = = Foo --- - .Foo = =
Foo
`
of dashes"/>
```````````````````````````````` The setext heading underline cannot be a [lazy continuation line] in a list item or block quote: ```````````````````````````````` example > Foo --- .Foo
```````````````````````````````` ```````````````````````````````` example - Foo --- .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 --- --- .foo
foo
Foo
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
foo
bar
foo
<a/>
*hi*
- one
chunk1
chunk2
chunk3
chunk1
chunk2
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 ---- .foo
foo
foo
bar
foo
foo
<
>
<
>
foo
aaa
~~~
aaa
```
aaa
```
aaa
~~~
```
aaa
aaa
bbb
```````````````````````````````` A code block can have all empty lines as its content: ```````````````````````````````` example ``` ``` .
aaa
aaa
aaa
aaa
aaa
aaa
aaa
aaa
```
aaa
```
aaa
aaa
aaa
```
aaa
aaa
~~~ ~~
foo
bar
baz
```````````````````````````````` Other blocks can also occur before and after fenced code blocks without an intervening blank line: ```````````````````````````````` example foo --- ~~~ bar ~~~ # baz .bar
def foo(x)
return 3
end
def foo(x)
return 3
end
aa
foo
foo
``` aaa
` within a HTML block started by `
