7321 lines
123 KiB
Text
7321 lines
123 KiB
Text
---
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title: CommonMark Spec
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author: John MacFarlane
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version: 0.17
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date: 2015-01-24
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license: '[CC-BY-SA 4.0](http://creativecommons.org/licenses/by-sa/4.0/)'
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...
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# Introduction
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## What is Markdown?
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Markdown is a plain text format for writing structured documents,
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based on conventions used for indicating formatting in email and
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usenet posts. It was developed in 2004 by John Gruber, who wrote
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the first Markdown-to-HTML converter in perl, and it soon became
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widely used in websites. By 2014 there were dozens of
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implementations in many languages. Some of them extended basic
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Markdown syntax with conventions for footnotes, definition lists,
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tables, and other constructs, and some allowed output not just in
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HTML but in LaTeX and many other formats.
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## Why is a spec needed?
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John Gruber's [canonical description of Markdown's
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syntax](http://daringfireball.net/projects/markdown/syntax)
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does not specify the syntax unambiguously. Here are some examples of
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questions it does not answer:
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1. How much indentation is needed for a sublist? The spec says that
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continuation paragraphs need to be indented four spaces, but is
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not fully explicit about sublists. It is natural to think that
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they, too, must be indented four spaces, but `Markdown.pl` does
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not require that. This is hardly a "corner case," and divergences
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between implementations on this issue often lead to surprises for
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users in real documents. (See [this comment by John
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Gruber](http://article.gmane.org/gmane.text.markdown.general/1997).)
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2. Is a blank line needed before a block quote or header?
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Most implementations do not require the blank line. However,
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this can lead to unexpected results in hard-wrapped text, and
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also to ambiguities in parsing (note that some implementations
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put the header inside the blockquote, while others do not).
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(John Gruber has also spoken [in favor of requiring the blank
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lines](http://article.gmane.org/gmane.text.markdown.general/2146).)
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3. Is a blank line needed before an indented code block?
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(`Markdown.pl` requires it, but this is not mentioned in the
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documentation, and some implementations do not require it.)
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``` markdown
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paragraph
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code?
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```
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4. What is the exact rule for determining when list items get
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wrapped in `<p>` tags? Can a list be partially "loose" and partially
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"tight"? What should we do with a list like this?
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``` markdown
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1. one
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2. two
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3. three
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```
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Or this?
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``` markdown
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1. one
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- a
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- b
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2. two
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```
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(There are some relevant comments by John Gruber
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[here](http://article.gmane.org/gmane.text.markdown.general/2554).)
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5. Can list markers be indented? Can ordered list markers be right-aligned?
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``` markdown
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8. item 1
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9. item 2
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10. item 2a
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```
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6. Is this one list with a horizontal rule in its second item,
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or two lists separated by a horizontal rule?
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``` markdown
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* a
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* * * * *
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* b
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```
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7. When list markers change from numbers to bullets, do we have
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two lists or one? (The Markdown syntax description suggests two,
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but the perl scripts and many other implementations produce one.)
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|
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``` markdown
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1. fee
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2. fie
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- foe
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- fum
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```
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8. What are the precedence rules for the markers of inline structure?
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For example, is the following a valid link, or does the code span
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take precedence ?
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``` markdown
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[a backtick (`)](/url) and [another backtick (`)](/url).
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```
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9. What are the precedence rules for markers of emphasis and strong
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emphasis? For example, how should the following be parsed?
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``` markdown
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*foo *bar* baz*
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```
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10. What are the precedence rules between block-level and inline-level
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structure? For example, how should the following be parsed?
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``` markdown
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- `a long code span can contain a hyphen like this
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- and it can screw things up`
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```
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11. Can list items include section headers? (`Markdown.pl` does not
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allow this, but does allow blockquotes to include headers.)
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``` markdown
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- # Heading
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```
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12. Can list items be empty?
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``` markdown
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* a
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*
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* b
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```
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13. Can link references be defined inside block quotes or list items?
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``` markdown
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> Blockquote [foo].
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>
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> [foo]: /url
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```
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14. If there are multiple definitions for the same reference, which takes
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precedence?
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``` markdown
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[foo]: /url1
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[foo]: /url2
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[foo][]
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```
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In the absence of a spec, early implementers consulted `Markdown.pl`
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to resolve these ambiguities. But `Markdown.pl` was quite buggy, and
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gave manifestly bad results in many cases, so it was not a
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satisfactory replacement for a spec.
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Because there is no unambiguous spec, implementations have diverged
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considerably. As a result, users are often surprised to find that
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a document that renders one way on one system (say, a github wiki)
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renders differently on another (say, converting to docbook using
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pandoc). To make matters worse, because nothing in Markdown counts
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as a "syntax error," the divergence often isn't discovered right away.
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## About this document
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This document attempts to specify Markdown syntax unambiguously.
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It contains many examples with side-by-side Markdown and
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HTML. These are intended to double as conformance tests. An
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accompanying script `spec_tests.py` can be used to run the tests
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against any Markdown program:
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python test/spec_tests.py --spec spec.txt --program PROGRAM
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Since this document describes how Markdown is to be parsed into
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an abstract syntax tree, it would have made sense to use an abstract
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representation of the syntax tree instead of HTML. But HTML is capable
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of representing the structural distinctions we need to make, and the
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choice of HTML for the tests makes it possible to run the tests against
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an implementation without writing an abstract syntax tree renderer.
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This document is generated from a text file, `spec.txt`, written
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in Markdown with a small extension for the side-by-side tests.
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The script `spec2md.pl` can be used to turn `spec.txt` into pandoc
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Markdown, which can then be converted into other formats.
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In the examples, the `→` character is used to represent tabs.
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# Preliminaries
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## Characters and lines
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Any sequence of [character]s is a valid CommonMark
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document.
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A [character](@character) is a unicode code point.
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This spec does not specify an encoding; it thinks of lines as composed
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of characters rather than bytes. A conforming parser may be limited
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to a certain encoding.
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A [line](@line) is a sequence of zero or more [character]s
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followed by a [line ending] or by the end of file.
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A [line ending](@line-ending) is, depending on the platform, a
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newline (`U+000A`), carriage return (`U+000D`), or
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carriage return + newline.
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For security reasons, a conforming parser must strip or replace the
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Unicode character `U+0000`.
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A line containing no characters, or a line containing only spaces
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(`U+0020`) or tabs (`U+0009`), is called a [blank line](@blank-line).
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The following definitions of character classes will be used in this spec:
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A [whitespace character](@whitespace-character) is a space
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(`U+0020`), tab (`U+0009`), carriage return (`U+000D`), or
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newline (`U+000A`).
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||
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[Whitespace](@whitespace) is a sequence of one or more [whitespace
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character]s.
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A [unicode whitespace character](@unicode-whitespace-character) is
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any code point in the unicode `Zs` class, or a tab (`U+0009`),
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carriage return (`U+000D`), newline (`U+000A`), or form feed
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(`U+000C`).
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[Unicode whitespace](@unicode-whitespace) is a sequence of one
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or more [unicode whitespace character]s.
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A [non-space character](@non-space-character) is anything but `U+0020`.
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An [ASCII punctuation character](@ascii-punctuation-character)
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is `!`, `"`, `#`, `$`, `%`, `&`, `'`, `(`, `)`,
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`*`, `+`, `,`, `-`, `.`, `/`, `:`, `;`, `<`, `=`, `>`, `?`, `@`,
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`[`, `\`, `]`, `^`, `_`, `` ` ``, `{`, `|`, `}`, or `~`.
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A [punctuation character](@punctuation-character) is an [ASCII
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punctuation character] or anything in
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the unicode classes `Pc`, `Pd`, `Pe`, `Pf`, `Pi`, `Po`, or `Ps`.
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## Tab expansion
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Tabs in lines are expanded to spaces, with a tab stop of 4 characters:
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.
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→foo→baz→→bim
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.
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<pre><code>foo baz bim
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</code></pre>
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.
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||
|
||
.
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a→a
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||
ὐ→a
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||
.
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||
<pre><code>a a
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ὐ a
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</code></pre>
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||
.
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||
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||
# Blocks and inlines
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||
We can think of a document as a sequence of
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[blocks](@block)---structural
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elements like paragraphs, block quotations,
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lists, headers, rules, and code blocks. Blocks can contain other
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blocks, or they can contain [inline](@inline) content:
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||
words, spaces, links, emphasized text, images, and inline code.
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## Precedence
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||
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Indicators of block structure always take precedence over indicators
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of inline structure. So, for example, the following is a list with
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two items, not a list with one item containing a code span:
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||
|
||
.
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- `one
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- two`
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||
.
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||
<ul>
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<li>`one</li>
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<li>two`</li>
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</ul>
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.
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This means that parsing can proceed in two steps: first, the block
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structure of the document can be discerned; second, text lines inside
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paragraphs, headers, and other block constructs can be parsed for inline
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structure. The second step requires information about link reference
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definitions that will be available only at the end of the first
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step. Note that the first step requires processing lines in sequence,
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but the second can be parallelized, since the inline parsing of
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one block element does not affect the inline parsing of any other.
|
||
|
||
## Container blocks and leaf blocks
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||
|
||
We can divide blocks into two types:
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[container block](@container-block)s,
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which can contain other blocks, and [leaf block](@leaf-block)s,
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which cannot.
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||
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# Leaf blocks
|
||
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This section describes the different kinds of leaf block that make up a
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Markdown document.
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||
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## Horizontal rules
|
||
|
||
A line consisting of 0-3 spaces of indentation, followed by a sequence
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of three or more matching `-`, `_`, or `*` characters, each followed
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optionally by any number of spaces, forms a
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[horizontal rule](@horizontal-rule).
|
||
|
||
.
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***
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||
---
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___
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||
.
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<hr />
|
||
<hr />
|
||
<hr />
|
||
.
|
||
|
||
Wrong characters:
|
||
|
||
.
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+++
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||
.
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<p>+++</p>
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||
.
|
||
|
||
.
|
||
===
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||
.
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<p>===</p>
|
||
.
|
||
|
||
Not enough characters:
|
||
|
||
.
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||
--
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||
**
|
||
__
|
||
.
|
||
<p>--
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||
**
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||
__</p>
|
||
.
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||
|
||
One to three spaces indent are allowed:
|
||
|
||
.
|
||
***
|
||
***
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||
***
|
||
.
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||
<hr />
|
||
<hr />
|
||
<hr />
|
||
.
|
||
|
||
Four spaces is too many:
|
||
|
||
.
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||
***
|
||
.
|
||
<pre><code>***
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
Foo
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||
***
|
||
.
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||
<p>Foo
|
||
***</p>
|
||
.
|
||
|
||
More than three characters may be used:
|
||
|
||
.
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||
_____________________________________
|
||
.
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||
<hr />
|
||
.
|
||
|
||
Spaces are allowed between the characters:
|
||
|
||
.
|
||
- - -
|
||
.
|
||
<hr />
|
||
.
|
||
|
||
.
|
||
** * ** * ** * **
|
||
.
|
||
<hr />
|
||
.
|
||
|
||
.
|
||
- - - -
|
||
.
|
||
<hr />
|
||
.
|
||
|
||
Spaces are allowed at the end:
|
||
|
||
.
|
||
- - - -
|
||
.
|
||
<hr />
|
||
.
|
||
|
||
However, no other characters may occur in the line:
|
||
|
||
.
|
||
_ _ _ _ a
|
||
|
||
a------
|
||
|
||
---a---
|
||
.
|
||
<p>_ _ _ _ a</p>
|
||
<p>a------</p>
|
||
<p>---a---</p>
|
||
.
|
||
|
||
It is required that all of the [non-space character]s be the same.
|
||
So, this is not a horizontal rule:
|
||
|
||
.
|
||
*-*
|
||
.
|
||
<p><em>-</em></p>
|
||
.
|
||
|
||
Horizontal rules do not need blank lines before or after:
|
||
|
||
.
|
||
- foo
|
||
***
|
||
- bar
|
||
.
|
||
<ul>
|
||
<li>foo</li>
|
||
</ul>
|
||
<hr />
|
||
<ul>
|
||
<li>bar</li>
|
||
</ul>
|
||
.
|
||
|
||
Horizontal rules can interrupt a paragraph:
|
||
|
||
.
|
||
Foo
|
||
***
|
||
bar
|
||
.
|
||
<p>Foo</p>
|
||
<hr />
|
||
<p>bar</p>
|
||
.
|
||
|
||
If a line of dashes that meets the above conditions for being a
|
||
horizontal rule could also be interpreted as the underline of a [setext
|
||
header], the interpretation as a
|
||
[setext header] takes precedence. Thus, for example,
|
||
this is a setext header, not a paragraph followed by a horizontal rule:
|
||
|
||
.
|
||
Foo
|
||
---
|
||
bar
|
||
.
|
||
<h2>Foo</h2>
|
||
<p>bar</p>
|
||
.
|
||
|
||
When both a horizontal rule and a list item are possible
|
||
interpretations of a line, the horizontal rule takes precedence:
|
||
|
||
.
|
||
* Foo
|
||
* * *
|
||
* Bar
|
||
.
|
||
<ul>
|
||
<li>Foo</li>
|
||
</ul>
|
||
<hr />
|
||
<ul>
|
||
<li>Bar</li>
|
||
</ul>
|
||
.
|
||
|
||
If you want a horizontal rule in a list item, use a different bullet:
|
||
|
||
.
|
||
- Foo
|
||
- * * *
|
||
.
|
||
<ul>
|
||
<li>Foo</li>
|
||
<li>
|
||
<hr />
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
## ATX headers
|
||
|
||
An [ATX header](@atx-header)
|
||
consists of a string of characters, parsed as inline content, between an
|
||
opening sequence of 1--6 unescaped `#` characters and an optional
|
||
closing sequence of any number of `#` characters. The opening sequence
|
||
of `#` characters cannot be followed directly by a
|
||
[non-space character].
|
||
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 header are stripped of leading and
|
||
trailing spaces before being parsed as inline content. The header level
|
||
is equal to the number of `#` characters in the opening sequence.
|
||
|
||
Simple headers:
|
||
|
||
.
|
||
# foo
|
||
## foo
|
||
### foo
|
||
#### foo
|
||
##### foo
|
||
###### foo
|
||
.
|
||
<h1>foo</h1>
|
||
<h2>foo</h2>
|
||
<h3>foo</h3>
|
||
<h4>foo</h4>
|
||
<h5>foo</h5>
|
||
<h6>foo</h6>
|
||
.
|
||
|
||
More than six `#` characters is not a header:
|
||
|
||
.
|
||
####### foo
|
||
.
|
||
<p>####### foo</p>
|
||
.
|
||
|
||
A space is required between the `#` characters and the header's
|
||
contents. Note that many implementations currently do not require
|
||
the space. However, the space was required by the [original ATX
|
||
implementation](http://www.aaronsw.com/2002/atx/atx.py), and it helps
|
||
prevent things like the following from being parsed as headers:
|
||
|
||
.
|
||
#5 bolt
|
||
.
|
||
<p>#5 bolt</p>
|
||
.
|
||
|
||
This is not a header, because the first `#` is escaped:
|
||
|
||
.
|
||
\## foo
|
||
.
|
||
<p>## foo</p>
|
||
.
|
||
|
||
Contents are parsed as inlines:
|
||
|
||
.
|
||
# foo *bar* \*baz\*
|
||
.
|
||
<h1>foo <em>bar</em> *baz*</h1>
|
||
.
|
||
|
||
Leading and trailing blanks are ignored in parsing inline content:
|
||
|
||
.
|
||
# foo
|
||
.
|
||
<h1>foo</h1>
|
||
.
|
||
|
||
One to three spaces indentation are allowed:
|
||
|
||
.
|
||
### foo
|
||
## foo
|
||
# foo
|
||
.
|
||
<h3>foo</h3>
|
||
<h2>foo</h2>
|
||
<h1>foo</h1>
|
||
.
|
||
|
||
Four spaces are too much:
|
||
|
||
.
|
||
# foo
|
||
.
|
||
<pre><code># foo
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
foo
|
||
# bar
|
||
.
|
||
<p>foo
|
||
# bar</p>
|
||
.
|
||
|
||
A closing sequence of `#` characters is optional:
|
||
|
||
.
|
||
## foo ##
|
||
### bar ###
|
||
.
|
||
<h2>foo</h2>
|
||
<h3>bar</h3>
|
||
.
|
||
|
||
It need not be the same length as the opening sequence:
|
||
|
||
.
|
||
# foo ##################################
|
||
##### foo ##
|
||
.
|
||
<h1>foo</h1>
|
||
<h5>foo</h5>
|
||
.
|
||
|
||
Spaces are allowed after the closing sequence:
|
||
|
||
.
|
||
### foo ###
|
||
.
|
||
<h3>foo</h3>
|
||
.
|
||
|
||
A sequence of `#` characters with a
|
||
[non-space character] following it
|
||
is not a closing sequence, but counts as part of the contents of the
|
||
header:
|
||
|
||
.
|
||
### foo ### b
|
||
.
|
||
<h3>foo ### b</h3>
|
||
.
|
||
|
||
The closing sequence must be preceded by a space:
|
||
|
||
.
|
||
# foo#
|
||
.
|
||
<h1>foo#</h1>
|
||
.
|
||
|
||
Backslash-escaped `#` characters do not count as part
|
||
of the closing sequence:
|
||
|
||
.
|
||
### foo \###
|
||
## foo #\##
|
||
# foo \#
|
||
.
|
||
<h3>foo ###</h3>
|
||
<h2>foo ###</h2>
|
||
<h1>foo #</h1>
|
||
.
|
||
|
||
ATX headers need not be separated from surrounding content by blank
|
||
lines, and they can interrupt paragraphs:
|
||
|
||
.
|
||
****
|
||
## foo
|
||
****
|
||
.
|
||
<hr />
|
||
<h2>foo</h2>
|
||
<hr />
|
||
.
|
||
|
||
.
|
||
Foo bar
|
||
# baz
|
||
Bar foo
|
||
.
|
||
<p>Foo bar</p>
|
||
<h1>baz</h1>
|
||
<p>Bar foo</p>
|
||
.
|
||
|
||
ATX headers can be empty:
|
||
|
||
.
|
||
##
|
||
#
|
||
### ###
|
||
.
|
||
<h2></h2>
|
||
<h1></h1>
|
||
<h3></h3>
|
||
.
|
||
|
||
## Setext headers
|
||
|
||
A [setext header](@setext-header)
|
||
consists of a line of text, containing at least one
|
||
[non-space character],
|
||
with no more than 3 spaces indentation, followed by a [setext header
|
||
underline]. The line of text must be
|
||
one that, were it not followed by the setext header underline,
|
||
would be interpreted as part of a paragraph: it cannot be a code
|
||
block, header, blockquote, horizontal rule, or list.
|
||
|
||
A [setext header underline](@setext-header-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 header underline].
|
||
|
||
The header is a level 1 header if `=` characters are used in the
|
||
[setext header underline], and a level 2
|
||
header if `-` characters are used. The contents of the header are the
|
||
result of parsing the first line as Markdown inline content.
|
||
|
||
In general, a setext header need not be preceded or followed by a
|
||
blank line. However, it cannot interrupt a paragraph, so when a
|
||
setext header comes after a paragraph, a blank line is needed between
|
||
them.
|
||
|
||
Simple examples:
|
||
|
||
.
|
||
Foo *bar*
|
||
=========
|
||
|
||
Foo *bar*
|
||
---------
|
||
.
|
||
<h1>Foo <em>bar</em></h1>
|
||
<h2>Foo <em>bar</em></h2>
|
||
.
|
||
|
||
The underlining can be any length:
|
||
|
||
.
|
||
Foo
|
||
-------------------------
|
||
|
||
Foo
|
||
=
|
||
.
|
||
<h2>Foo</h2>
|
||
<h1>Foo</h1>
|
||
.
|
||
|
||
The header content can be indented up to three spaces, and need
|
||
not line up with the underlining:
|
||
|
||
.
|
||
Foo
|
||
---
|
||
|
||
Foo
|
||
-----
|
||
|
||
Foo
|
||
===
|
||
.
|
||
<h2>Foo</h2>
|
||
<h2>Foo</h2>
|
||
<h1>Foo</h1>
|
||
.
|
||
|
||
Four spaces indent is too much:
|
||
|
||
.
|
||
Foo
|
||
---
|
||
|
||
Foo
|
||
---
|
||
.
|
||
<pre><code>Foo
|
||
---
|
||
|
||
Foo
|
||
</code></pre>
|
||
<hr />
|
||
.
|
||
|
||
The setext header underline can be indented up to three spaces, and
|
||
may have trailing spaces:
|
||
|
||
.
|
||
Foo
|
||
----
|
||
.
|
||
<h2>Foo</h2>
|
||
.
|
||
|
||
Four spaces is too much:
|
||
|
||
.
|
||
Foo
|
||
---
|
||
.
|
||
<p>Foo
|
||
---</p>
|
||
.
|
||
|
||
The setext header underline cannot contain internal spaces:
|
||
|
||
.
|
||
Foo
|
||
= =
|
||
|
||
Foo
|
||
--- -
|
||
.
|
||
<p>Foo
|
||
= =</p>
|
||
<p>Foo</p>
|
||
<hr />
|
||
.
|
||
|
||
Trailing spaces in the content line do not cause a line break:
|
||
|
||
.
|
||
Foo
|
||
-----
|
||
.
|
||
<h2>Foo</h2>
|
||
.
|
||
|
||
Nor does a backslash at the end:
|
||
|
||
.
|
||
Foo\
|
||
----
|
||
.
|
||
<h2>Foo\</h2>
|
||
.
|
||
|
||
Since indicators of block structure take precedence over
|
||
indicators of inline structure, the following are setext headers:
|
||
|
||
.
|
||
`Foo
|
||
----
|
||
`
|
||
|
||
<a title="a lot
|
||
---
|
||
of dashes"/>
|
||
.
|
||
<h2>`Foo</h2>
|
||
<p>`</p>
|
||
<h2><a title="a lot</h2>
|
||
<p>of dashes"/></p>
|
||
.
|
||
|
||
The setext header underline cannot be a [lazy continuation
|
||
line] in a list item or block quote:
|
||
|
||
.
|
||
> Foo
|
||
---
|
||
.
|
||
<blockquote>
|
||
<p>Foo</p>
|
||
</blockquote>
|
||
<hr />
|
||
.
|
||
|
||
.
|
||
- Foo
|
||
---
|
||
.
|
||
<ul>
|
||
<li>Foo</li>
|
||
</ul>
|
||
<hr />
|
||
.
|
||
|
||
A setext header cannot interrupt a paragraph:
|
||
|
||
.
|
||
Foo
|
||
Bar
|
||
---
|
||
|
||
Foo
|
||
Bar
|
||
===
|
||
.
|
||
<p>Foo
|
||
Bar</p>
|
||
<hr />
|
||
<p>Foo
|
||
Bar
|
||
===</p>
|
||
.
|
||
|
||
But in general a blank line is not required before or after:
|
||
|
||
.
|
||
---
|
||
Foo
|
||
---
|
||
Bar
|
||
---
|
||
Baz
|
||
.
|
||
<hr />
|
||
<h2>Foo</h2>
|
||
<h2>Bar</h2>
|
||
<p>Baz</p>
|
||
.
|
||
|
||
Setext headers cannot be empty:
|
||
|
||
.
|
||
|
||
====
|
||
.
|
||
<p>====</p>
|
||
.
|
||
|
||
Setext header text lines must not be interpretable as block
|
||
constructs other than paragraphs. So, the line of dashes
|
||
in these examples gets interpreted as a horizontal rule:
|
||
|
||
.
|
||
---
|
||
---
|
||
.
|
||
<hr />
|
||
<hr />
|
||
.
|
||
|
||
.
|
||
- foo
|
||
-----
|
||
.
|
||
<ul>
|
||
<li>foo</li>
|
||
</ul>
|
||
<hr />
|
||
.
|
||
|
||
.
|
||
foo
|
||
---
|
||
.
|
||
<pre><code>foo
|
||
</code></pre>
|
||
<hr />
|
||
.
|
||
|
||
.
|
||
> foo
|
||
-----
|
||
.
|
||
<blockquote>
|
||
<p>foo</p>
|
||
</blockquote>
|
||
<hr />
|
||
.
|
||
|
||
If you want a header with `> foo` as its literal text, you can
|
||
use backslash escapes:
|
||
|
||
.
|
||
\> foo
|
||
------
|
||
.
|
||
<h2>> foo</h2>
|
||
.
|
||
|
||
## Indented code blocks
|
||
|
||
An [indented code block](@indented-code-block) is composed of one or more
|
||
[indented chunk]s separated by blank lines.
|
||
An [indented chunk](@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 ending]s, 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.)
|
||
|
||
.
|
||
a simple
|
||
indented code block
|
||
.
|
||
<pre><code>a simple
|
||
indented code block
|
||
</code></pre>
|
||
.
|
||
|
||
The contents are literal text, and do not get parsed as Markdown:
|
||
|
||
.
|
||
<a/>
|
||
*hi*
|
||
|
||
- one
|
||
.
|
||
<pre><code><a/>
|
||
*hi*
|
||
|
||
- one
|
||
</code></pre>
|
||
.
|
||
|
||
Here we have three chunks separated by blank lines:
|
||
|
||
.
|
||
chunk1
|
||
|
||
chunk2
|
||
|
||
|
||
|
||
chunk3
|
||
.
|
||
<pre><code>chunk1
|
||
|
||
chunk2
|
||
|
||
|
||
|
||
chunk3
|
||
</code></pre>
|
||
.
|
||
|
||
Any initial spaces beyond four will be included in the content, even
|
||
in interior blank lines:
|
||
|
||
.
|
||
chunk1
|
||
|
||
chunk2
|
||
.
|
||
<pre><code>chunk1
|
||
|
||
chunk2
|
||
</code></pre>
|
||
.
|
||
|
||
An indented code block cannot interrupt a paragraph. (This
|
||
allows hanging indents and the like.)
|
||
|
||
.
|
||
Foo
|
||
bar
|
||
|
||
.
|
||
<p>Foo
|
||
bar</p>
|
||
.
|
||
|
||
However, any non-blank line with fewer than four leading spaces ends
|
||
the code block immediately. So a paragraph may occur immediately
|
||
after indented code:
|
||
|
||
.
|
||
foo
|
||
bar
|
||
.
|
||
<pre><code>foo
|
||
</code></pre>
|
||
<p>bar</p>
|
||
.
|
||
|
||
And indented code can occur immediately before and after other kinds of
|
||
blocks:
|
||
|
||
.
|
||
# Header
|
||
foo
|
||
Header
|
||
------
|
||
foo
|
||
----
|
||
.
|
||
<h1>Header</h1>
|
||
<pre><code>foo
|
||
</code></pre>
|
||
<h2>Header</h2>
|
||
<pre><code>foo
|
||
</code></pre>
|
||
<hr />
|
||
.
|
||
|
||
The first line can be indented more than four spaces:
|
||
|
||
.
|
||
foo
|
||
bar
|
||
.
|
||
<pre><code> foo
|
||
bar
|
||
</code></pre>
|
||
.
|
||
|
||
Blank lines preceding or following an indented code block
|
||
are not included in it:
|
||
|
||
.
|
||
|
||
|
||
foo
|
||
|
||
|
||
.
|
||
<pre><code>foo
|
||
</code></pre>
|
||
.
|
||
|
||
Trailing spaces are included in the code block's content:
|
||
|
||
.
|
||
foo
|
||
.
|
||
<pre><code>foo
|
||
</code></pre>
|
||
.
|
||
|
||
|
||
## Fenced code blocks
|
||
|
||
A [code fence](@code-fence) is a sequence
|
||
of at least three consecutive backtick characters (`` ` ``) or
|
||
tildes (`~`). (Tildes and backticks cannot be mixed.)
|
||
A [fenced code block](@fenced-code-block)
|
||
begins with a code fence, indented no more than three spaces.
|
||
|
||
The line with the opening code fence may optionally contain some text
|
||
following the code fence; this is trimmed of leading and trailing
|
||
spaces and called the [info string](@info-string).
|
||
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:
|
||
|
||
.
|
||
```
|
||
<
|
||
>
|
||
```
|
||
.
|
||
<pre><code><
|
||
>
|
||
</code></pre>
|
||
.
|
||
|
||
With tildes:
|
||
|
||
.
|
||
~~~
|
||
<
|
||
>
|
||
~~~
|
||
.
|
||
<pre><code><
|
||
>
|
||
</code></pre>
|
||
.
|
||
|
||
The closing code fence must use the same character as the opening
|
||
fence:
|
||
|
||
.
|
||
```
|
||
aaa
|
||
~~~
|
||
```
|
||
.
|
||
<pre><code>aaa
|
||
~~~
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
~~~
|
||
aaa
|
||
```
|
||
~~~
|
||
.
|
||
<pre><code>aaa
|
||
```
|
||
</code></pre>
|
||
.
|
||
|
||
The closing code fence must be at least as long as the opening fence:
|
||
|
||
.
|
||
````
|
||
aaa
|
||
```
|
||
``````
|
||
.
|
||
<pre><code>aaa
|
||
```
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
~~~~
|
||
aaa
|
||
~~~
|
||
~~~~
|
||
.
|
||
<pre><code>aaa
|
||
~~~
|
||
</code></pre>
|
||
.
|
||
|
||
Unclosed code blocks are closed by the end of the document:
|
||
|
||
.
|
||
```
|
||
.
|
||
<pre><code></code></pre>
|
||
.
|
||
|
||
.
|
||
`````
|
||
|
||
```
|
||
aaa
|
||
.
|
||
<pre><code>
|
||
```
|
||
aaa
|
||
</code></pre>
|
||
.
|
||
|
||
A code block can have all empty lines as its content:
|
||
|
||
.
|
||
```
|
||
|
||
|
||
```
|
||
.
|
||
<pre><code>
|
||
|
||
</code></pre>
|
||
.
|
||
|
||
A code block can be empty:
|
||
|
||
.
|
||
```
|
||
```
|
||
.
|
||
<pre><code></code></pre>
|
||
.
|
||
|
||
Fences can be indented. If the opening fence is indented,
|
||
content lines will have equivalent opening indentation removed,
|
||
if present:
|
||
|
||
.
|
||
```
|
||
aaa
|
||
aaa
|
||
```
|
||
.
|
||
<pre><code>aaa
|
||
aaa
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
```
|
||
aaa
|
||
aaa
|
||
aaa
|
||
```
|
||
.
|
||
<pre><code>aaa
|
||
aaa
|
||
aaa
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
```
|
||
aaa
|
||
aaa
|
||
aaa
|
||
```
|
||
.
|
||
<pre><code>aaa
|
||
aaa
|
||
aaa
|
||
</code></pre>
|
||
.
|
||
|
||
Four spaces indentation produces an indented code block:
|
||
|
||
.
|
||
```
|
||
aaa
|
||
```
|
||
.
|
||
<pre><code>```
|
||
aaa
|
||
```
|
||
</code></pre>
|
||
.
|
||
|
||
Closing fences may be indented by 0-3 spaces, and their indentation
|
||
need not match that of the opening fence:
|
||
|
||
.
|
||
```
|
||
aaa
|
||
```
|
||
.
|
||
<pre><code>aaa
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
```
|
||
aaa
|
||
```
|
||
.
|
||
<pre><code>aaa
|
||
</code></pre>
|
||
.
|
||
|
||
This is not a closing fence, because it is indented 4 spaces:
|
||
|
||
.
|
||
```
|
||
aaa
|
||
```
|
||
.
|
||
<pre><code>aaa
|
||
```
|
||
</code></pre>
|
||
.
|
||
|
||
|
||
Code fences (opening and closing) cannot contain internal spaces:
|
||
|
||
.
|
||
``` ```
|
||
aaa
|
||
.
|
||
<p><code></code>
|
||
aaa</p>
|
||
.
|
||
|
||
.
|
||
~~~~~~
|
||
aaa
|
||
~~~ ~~
|
||
.
|
||
<pre><code>aaa
|
||
~~~ ~~
|
||
</code></pre>
|
||
.
|
||
|
||
Fenced code blocks can interrupt paragraphs, and can be followed
|
||
directly by paragraphs, without a blank line between:
|
||
|
||
.
|
||
foo
|
||
```
|
||
bar
|
||
```
|
||
baz
|
||
.
|
||
<p>foo</p>
|
||
<pre><code>bar
|
||
</code></pre>
|
||
<p>baz</p>
|
||
.
|
||
|
||
Other blocks can also occur before and after fenced code blocks
|
||
without an intervening blank line:
|
||
|
||
.
|
||
foo
|
||
---
|
||
~~~
|
||
bar
|
||
~~~
|
||
# baz
|
||
.
|
||
<h2>foo</h2>
|
||
<pre><code>bar
|
||
</code></pre>
|
||
<h1>baz</h1>
|
||
.
|
||
|
||
An [info string] can be provided after the opening code fence.
|
||
Opening and closing spaces will be stripped, and the first word, prefixed
|
||
with `language-`, is used as the value for the `class` attribute of the
|
||
`code` element within the enclosing `pre` element.
|
||
|
||
.
|
||
```ruby
|
||
def foo(x)
|
||
return 3
|
||
end
|
||
```
|
||
.
|
||
<pre><code class="language-ruby">def foo(x)
|
||
return 3
|
||
end
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
~~~~ ruby startline=3 $%@#$
|
||
def foo(x)
|
||
return 3
|
||
end
|
||
~~~~~~~
|
||
.
|
||
<pre><code class="language-ruby">def foo(x)
|
||
return 3
|
||
end
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
````;
|
||
````
|
||
.
|
||
<pre><code class="language-;"></code></pre>
|
||
.
|
||
|
||
[Info string]s for backtick code blocks cannot contain backticks:
|
||
|
||
.
|
||
``` aa ```
|
||
foo
|
||
.
|
||
<p><code>aa</code>
|
||
foo</p>
|
||
.
|
||
|
||
Closing code fences cannot have [info string]s:
|
||
|
||
.
|
||
```
|
||
``` aaa
|
||
```
|
||
.
|
||
<pre><code>``` aaa
|
||
</code></pre>
|
||
.
|
||
|
||
|
||
## HTML blocks
|
||
|
||
An [HTML block tag](@html-block-tag) is
|
||
an [open tag] or [closing tag] whose tag
|
||
name is one of the following (case-insensitive):
|
||
`article`, `header`, `aside`, `hgroup`, `blockquote`, `hr`, `iframe`,
|
||
`body`, `li`, `map`, `button`, `object`, `canvas`, `ol`, `caption`,
|
||
`output`, `col`, `p`, `colgroup`, `pre`, `dd`, `progress`, `div`,
|
||
`section`, `dl`, `table`, `td`, `dt`, `tbody`, `embed`, `textarea`,
|
||
`fieldset`, `tfoot`, `figcaption`, `th`, `figure`, `thead`, `footer`,
|
||
`tr`, `form`, `ul`, `h1`, `h2`, `h3`, `h4`, `h5`, `h6`, `video`,
|
||
`script`, `style`.
|
||
|
||
An [HTML block](@html-block) begins with an
|
||
[HTML block tag], [HTML comment], [processing instruction],
|
||
[declaration], or [CDATA section].
|
||
It ends when a [blank line] or the end of the
|
||
input is encountered. The initial line may be indented up to three
|
||
spaces, and subsequent lines may have any indentation. The contents
|
||
of the HTML block are interpreted as raw HTML, and will not be escaped
|
||
in HTML output.
|
||
|
||
Some simple examples:
|
||
|
||
.
|
||
<table>
|
||
<tr>
|
||
<td>
|
||
hi
|
||
</td>
|
||
</tr>
|
||
</table>
|
||
|
||
okay.
|
||
.
|
||
<table>
|
||
<tr>
|
||
<td>
|
||
hi
|
||
</td>
|
||
</tr>
|
||
</table>
|
||
<p>okay.</p>
|
||
.
|
||
|
||
.
|
||
<div>
|
||
*hello*
|
||
<foo><a>
|
||
.
|
||
<div>
|
||
*hello*
|
||
<foo><a>
|
||
.
|
||
|
||
Here we have two HTML blocks with a Markdown paragraph between them:
|
||
|
||
.
|
||
<DIV CLASS="foo">
|
||
|
||
*Markdown*
|
||
|
||
</DIV>
|
||
.
|
||
<DIV CLASS="foo">
|
||
<p><em>Markdown</em></p>
|
||
</DIV>
|
||
.
|
||
|
||
In the following example, what looks like a Markdown code block
|
||
is actually part of the HTML block, which continues until a blank
|
||
line or the end of the document is reached:
|
||
|
||
.
|
||
<div></div>
|
||
``` c
|
||
int x = 33;
|
||
```
|
||
.
|
||
<div></div>
|
||
``` c
|
||
int x = 33;
|
||
```
|
||
.
|
||
|
||
A comment:
|
||
|
||
.
|
||
<!-- Foo
|
||
bar
|
||
baz -->
|
||
.
|
||
<!-- Foo
|
||
bar
|
||
baz -->
|
||
.
|
||
|
||
A processing instruction:
|
||
|
||
.
|
||
<?php
|
||
echo '>';
|
||
?>
|
||
.
|
||
<?php
|
||
echo '>';
|
||
?>
|
||
.
|
||
|
||
CDATA:
|
||
|
||
.
|
||
<![CDATA[
|
||
function matchwo(a,b)
|
||
{
|
||
if (a < b && a < 0) then
|
||
{
|
||
return 1;
|
||
}
|
||
else
|
||
{
|
||
return 0;
|
||
}
|
||
}
|
||
]]>
|
||
.
|
||
<![CDATA[
|
||
function matchwo(a,b)
|
||
{
|
||
if (a < b && a < 0) then
|
||
{
|
||
return 1;
|
||
}
|
||
else
|
||
{
|
||
return 0;
|
||
}
|
||
}
|
||
]]>
|
||
.
|
||
|
||
The opening tag can be indented 1-3 spaces, but not 4:
|
||
|
||
.
|
||
<!-- foo -->
|
||
|
||
<!-- foo -->
|
||
.
|
||
<!-- foo -->
|
||
<pre><code><!-- foo -->
|
||
</code></pre>
|
||
.
|
||
|
||
An HTML block can interrupt a paragraph, and need not be preceded
|
||
by a blank line.
|
||
|
||
.
|
||
Foo
|
||
<div>
|
||
bar
|
||
</div>
|
||
.
|
||
<p>Foo</p>
|
||
<div>
|
||
bar
|
||
</div>
|
||
.
|
||
|
||
However, a following blank line is always needed, except at the end of
|
||
a document:
|
||
|
||
.
|
||
<div>
|
||
bar
|
||
</div>
|
||
*foo*
|
||
.
|
||
<div>
|
||
bar
|
||
</div>
|
||
*foo*
|
||
.
|
||
|
||
An incomplete HTML block tag may also start an HTML block:
|
||
|
||
.
|
||
<div class
|
||
foo
|
||
.
|
||
<div class
|
||
foo
|
||
.
|
||
|
||
This rule differs from John Gruber's original Markdown syntax
|
||
specification, which says:
|
||
|
||
> The only restrictions are that block-level HTML elements —
|
||
> e.g. `<div>`, `<table>`, `<pre>`, `<p>`, etc. — must be separated from
|
||
> surrounding content by blank lines, and the start and end tags of the
|
||
> block should not be indented with tabs or spaces.
|
||
|
||
In some ways Gruber's rule is more restrictive than the one given
|
||
here:
|
||
|
||
- It requires that an HTML block be preceded by a blank line.
|
||
- It does not allow the start tag to be indented.
|
||
- It requires a matching end tag, which it also does not allow to
|
||
be indented.
|
||
|
||
Indeed, most Markdown implementations, including some of Gruber's
|
||
own perl implementations, do not impose these restrictions.
|
||
|
||
There is one respect, however, in which Gruber's rule is more liberal
|
||
than the one given here, since it allows blank lines to occur inside
|
||
an HTML block. There are two reasons for disallowing them here.
|
||
First, it removes the need to parse balanced tags, which is
|
||
expensive and can require backtracking from the end of the document
|
||
if no matching end tag is found. Second, it provides a very simple
|
||
and flexible way of including Markdown content inside HTML tags:
|
||
simply separate the Markdown from the HTML using blank lines:
|
||
|
||
.
|
||
<div>
|
||
|
||
*Emphasized* text.
|
||
|
||
</div>
|
||
.
|
||
<div>
|
||
<p><em>Emphasized</em> text.</p>
|
||
</div>
|
||
.
|
||
|
||
Compare:
|
||
|
||
.
|
||
<div>
|
||
*Emphasized* text.
|
||
</div>
|
||
.
|
||
<div>
|
||
*Emphasized* text.
|
||
</div>
|
||
.
|
||
|
||
Some Markdown implementations have adopted a convention of
|
||
interpreting content inside tags as text if the open tag has
|
||
the attribute `markdown=1`. The rule given above seems a simpler and
|
||
more elegant way of achieving the same expressive power, which is also
|
||
much simpler to parse.
|
||
|
||
The main potential drawback is that one can no longer paste HTML
|
||
blocks into Markdown documents with 100% reliability. However,
|
||
*in most cases* this will work fine, because the blank lines in
|
||
HTML are usually followed by HTML block tags. For example:
|
||
|
||
.
|
||
<table>
|
||
|
||
<tr>
|
||
|
||
<td>
|
||
Hi
|
||
</td>
|
||
|
||
</tr>
|
||
|
||
</table>
|
||
.
|
||
<table>
|
||
<tr>
|
||
<td>
|
||
Hi
|
||
</td>
|
||
</tr>
|
||
</table>
|
||
.
|
||
|
||
Moreover, blank lines are usually not necessary and can be
|
||
deleted. The exception is inside `<pre>` tags; here, one can
|
||
replace the blank lines with ` ` entities.
|
||
|
||
So there is no important loss of expressive power with the new rule.
|
||
|
||
## Link reference definitions
|
||
|
||
A [link reference definition](@link-reference-definition)
|
||
consists of a [link label], indented up to three spaces, followed
|
||
by a colon (`:`), optional [whitespace] (including up to one
|
||
[line ending]), a [link destination],
|
||
optional [whitespace] (including up to one
|
||
[line ending]), and an optional [link
|
||
title], which if it is present must be separated
|
||
from the [link destination] by [whitespace].
|
||
No further [non-space character]s may occur on the line.
|
||
|
||
A [link reference-definition]
|
||
does not correspond to a structural element of a document. Instead, it
|
||
defines a label which can be used in [reference link]s
|
||
and reference-style [images] elsewhere in the document. [Link
|
||
reference definitions] can come either before or after the links that use
|
||
them.
|
||
|
||
.
|
||
[foo]: /url "title"
|
||
|
||
[foo]
|
||
.
|
||
<p><a href="/url" title="title">foo</a></p>
|
||
.
|
||
|
||
.
|
||
[foo]:
|
||
/url
|
||
'the title'
|
||
|
||
[foo]
|
||
.
|
||
<p><a href="/url" title="the title">foo</a></p>
|
||
.
|
||
|
||
.
|
||
[Foo*bar\]]:my_(url) 'title (with parens)'
|
||
|
||
[Foo*bar\]]
|
||
.
|
||
<p><a href="my_(url)" title="title (with parens)">Foo*bar]</a></p>
|
||
.
|
||
|
||
.
|
||
[Foo bar]:
|
||
<my url>
|
||
'title'
|
||
|
||
[Foo bar]
|
||
.
|
||
<p><a href="my%20url" title="title">Foo bar</a></p>
|
||
.
|
||
|
||
The title may be omitted:
|
||
|
||
.
|
||
[foo]:
|
||
/url
|
||
|
||
[foo]
|
||
.
|
||
<p><a href="/url">foo</a></p>
|
||
.
|
||
|
||
The link destination may not be omitted:
|
||
|
||
.
|
||
[foo]:
|
||
|
||
[foo]
|
||
.
|
||
<p>[foo]:</p>
|
||
<p>[foo]</p>
|
||
.
|
||
|
||
A link can come before its corresponding definition:
|
||
|
||
.
|
||
[foo]
|
||
|
||
[foo]: url
|
||
.
|
||
<p><a href="url">foo</a></p>
|
||
.
|
||
|
||
If there are several matching definitions, the first one takes
|
||
precedence:
|
||
|
||
.
|
||
[foo]
|
||
|
||
[foo]: first
|
||
[foo]: second
|
||
.
|
||
<p><a href="first">foo</a></p>
|
||
.
|
||
|
||
As noted in the section on [Links], matching of labels is
|
||
case-insensitive (see [matches]).
|
||
|
||
.
|
||
[FOO]: /url
|
||
|
||
[Foo]
|
||
.
|
||
<p><a href="/url">Foo</a></p>
|
||
.
|
||
|
||
.
|
||
[ΑΓΩ]: /φου
|
||
|
||
[αγω]
|
||
.
|
||
<p><a href="/%CF%86%CE%BF%CF%85">αγω</a></p>
|
||
.
|
||
|
||
Here is a link reference definition with no corresponding link.
|
||
It contributes nothing to the document.
|
||
|
||
.
|
||
[foo]: /url
|
||
.
|
||
.
|
||
|
||
This is not a link reference definition, because there are
|
||
[non-space character]s after the title:
|
||
|
||
.
|
||
[foo]: /url "title" ok
|
||
.
|
||
<p>[foo]: /url "title" ok</p>
|
||
.
|
||
|
||
This is not a link reference definition, because it is indented
|
||
four spaces:
|
||
|
||
.
|
||
[foo]: /url "title"
|
||
|
||
[foo]
|
||
.
|
||
<pre><code>[foo]: /url "title"
|
||
</code></pre>
|
||
<p>[foo]</p>
|
||
.
|
||
|
||
This is not a link reference definition, because it occurs inside
|
||
a code block:
|
||
|
||
.
|
||
```
|
||
[foo]: /url
|
||
```
|
||
|
||
[foo]
|
||
.
|
||
<pre><code>[foo]: /url
|
||
</code></pre>
|
||
<p>[foo]</p>
|
||
.
|
||
|
||
A [link reference definition] cannot interrupt a paragraph.
|
||
|
||
.
|
||
Foo
|
||
[bar]: /baz
|
||
|
||
[bar]
|
||
.
|
||
<p>Foo
|
||
[bar]: /baz</p>
|
||
<p>[bar]</p>
|
||
.
|
||
|
||
However, it can directly follow other block elements, such as headers
|
||
and horizontal rules, and it need not be followed by a blank line.
|
||
|
||
.
|
||
# [Foo]
|
||
[foo]: /url
|
||
> bar
|
||
.
|
||
<h1><a href="/url">Foo</a></h1>
|
||
<blockquote>
|
||
<p>bar</p>
|
||
</blockquote>
|
||
.
|
||
|
||
Several [link reference definition]s
|
||
can occur one after another, without intervening blank lines.
|
||
|
||
.
|
||
[foo]: /foo-url "foo"
|
||
[bar]: /bar-url
|
||
"bar"
|
||
[baz]: /baz-url
|
||
|
||
[foo],
|
||
[bar],
|
||
[baz]
|
||
.
|
||
<p><a href="/foo-url" title="foo">foo</a>,
|
||
<a href="/bar-url" title="bar">bar</a>,
|
||
<a href="/baz-url">baz</a></p>
|
||
.
|
||
|
||
[Link reference definition]s can occur
|
||
inside block containers, like lists and block quotations. They
|
||
affect the entire document, not just the container in which they
|
||
are defined:
|
||
|
||
.
|
||
[foo]
|
||
|
||
> [foo]: /url
|
||
.
|
||
<p><a href="/url">foo</a></p>
|
||
<blockquote>
|
||
</blockquote>
|
||
.
|
||
|
||
|
||
## Paragraphs
|
||
|
||
A sequence of non-blank lines that cannot be interpreted as other
|
||
kinds of blocks forms a [paragraph](@paragraph).
|
||
The contents of the paragraph are the result of parsing the
|
||
paragraph's raw content as inlines. The paragraph's raw content
|
||
is formed by concatenating the lines and removing initial and final
|
||
[whitespace].
|
||
|
||
A simple example with two paragraphs:
|
||
|
||
.
|
||
aaa
|
||
|
||
bbb
|
||
.
|
||
<p>aaa</p>
|
||
<p>bbb</p>
|
||
.
|
||
|
||
Paragraphs can contain multiple lines, but no blank lines:
|
||
|
||
.
|
||
aaa
|
||
bbb
|
||
|
||
ccc
|
||
ddd
|
||
.
|
||
<p>aaa
|
||
bbb</p>
|
||
<p>ccc
|
||
ddd</p>
|
||
.
|
||
|
||
Multiple blank lines between paragraph have no effect:
|
||
|
||
.
|
||
aaa
|
||
|
||
|
||
bbb
|
||
.
|
||
<p>aaa</p>
|
||
<p>bbb</p>
|
||
.
|
||
|
||
Leading spaces are skipped:
|
||
|
||
.
|
||
aaa
|
||
bbb
|
||
.
|
||
<p>aaa
|
||
bbb</p>
|
||
.
|
||
|
||
Lines after the first may be indented any amount, since indented
|
||
code blocks cannot interrupt paragraphs.
|
||
|
||
.
|
||
aaa
|
||
bbb
|
||
ccc
|
||
.
|
||
<p>aaa
|
||
bbb
|
||
ccc</p>
|
||
.
|
||
|
||
However, the first line may be indented at most three spaces,
|
||
or an indented code block will be triggered:
|
||
|
||
.
|
||
aaa
|
||
bbb
|
||
.
|
||
<p>aaa
|
||
bbb</p>
|
||
.
|
||
|
||
.
|
||
aaa
|
||
bbb
|
||
.
|
||
<pre><code>aaa
|
||
</code></pre>
|
||
<p>bbb</p>
|
||
.
|
||
|
||
Final spaces are stripped before inline parsing, so a paragraph
|
||
that ends with two or more spaces will not end with a [hard line
|
||
break]:
|
||
|
||
.
|
||
aaa
|
||
bbb
|
||
.
|
||
<p>aaa<br />
|
||
bbb</p>
|
||
.
|
||
|
||
## Blank lines
|
||
|
||
[Blank line]s between block-level elements are ignored,
|
||
except for the role they play in determining whether a [list]
|
||
is [tight] or [loose].
|
||
|
||
Blank lines at the beginning and end of the document are also ignored.
|
||
|
||
.
|
||
|
||
|
||
aaa
|
||
|
||
|
||
# aaa
|
||
|
||
|
||
.
|
||
<p>aaa</p>
|
||
<h1>aaa</h1>
|
||
.
|
||
|
||
|
||
# Container blocks
|
||
|
||
A [container block] is a block that has other
|
||
blocks as its contents. There are two basic kinds of container blocks:
|
||
[block quotes] and [list items].
|
||
[Lists] are meta-containers for [list items].
|
||
|
||
We define the syntax for container blocks recursively. The general
|
||
form of the definition is:
|
||
|
||
> If X is a sequence of blocks, then the result of
|
||
> transforming X in such-and-such a way is a container of type Y
|
||
> with these blocks as its content.
|
||
|
||
So, we explain what counts as a block quote or list item by explaining
|
||
how these can be *generated* from their contents. This should suffice
|
||
to define the syntax, although it does not give a recipe for *parsing*
|
||
these constructions. (A recipe is provided below in the section entitled
|
||
[A parsing strategy](#appendix-a-a-parsing-strategy).)
|
||
|
||
## Block quotes
|
||
|
||
A [block quote marker](@block-quote-marker)
|
||
consists of 0-3 spaces of initial indent, plus (a) the character `>` together
|
||
with a following space, or (b) a single character `>` not followed by a space.
|
||
|
||
The following rules define [block quotes]:
|
||
|
||
1. **Basic case.** If a string of lines *Ls* constitute a sequence
|
||
of blocks *Bs*, then the result of prepending a [block quote
|
||
marker] to the beginning of each line in *Ls*
|
||
is a [block quote](#block-quotes) containing *Bs*.
|
||
|
||
2. **Laziness.** If a string of lines *Ls* constitute a [block
|
||
quote](#block-quotes) with contents *Bs*, then the result of deleting
|
||
the initial [block quote marker] from one or
|
||
more lines in which the next [non-space character] after the [block
|
||
quote marker] is [paragraph continuation
|
||
text] is a block quote with *Bs* as its content.
|
||
[Paragraph continuation text](@paragraph-continuation-text) is text
|
||
that will be parsed as part of the content of a paragraph, but does
|
||
not occur at the beginning of the paragraph.
|
||
|
||
3. **Consecutiveness.** A document cannot contain two [block
|
||
quotes] in a row unless there is a [blank line] between them.
|
||
|
||
Nothing else counts as a [block quote](#block-quotes).
|
||
|
||
Here is a simple example:
|
||
|
||
.
|
||
> # Foo
|
||
> bar
|
||
> baz
|
||
.
|
||
<blockquote>
|
||
<h1>Foo</h1>
|
||
<p>bar
|
||
baz</p>
|
||
</blockquote>
|
||
.
|
||
|
||
The spaces after the `>` characters can be omitted:
|
||
|
||
.
|
||
># Foo
|
||
>bar
|
||
> baz
|
||
.
|
||
<blockquote>
|
||
<h1>Foo</h1>
|
||
<p>bar
|
||
baz</p>
|
||
</blockquote>
|
||
.
|
||
|
||
The `>` characters can be indented 1-3 spaces:
|
||
|
||
.
|
||
> # Foo
|
||
> bar
|
||
> baz
|
||
.
|
||
<blockquote>
|
||
<h1>Foo</h1>
|
||
<p>bar
|
||
baz</p>
|
||
</blockquote>
|
||
.
|
||
|
||
Four spaces gives us a code block:
|
||
|
||
.
|
||
> # Foo
|
||
> bar
|
||
> baz
|
||
.
|
||
<pre><code>> # Foo
|
||
> bar
|
||
> baz
|
||
</code></pre>
|
||
.
|
||
|
||
The Laziness clause allows us to omit the `>` before a
|
||
paragraph continuation line:
|
||
|
||
.
|
||
> # Foo
|
||
> bar
|
||
baz
|
||
.
|
||
<blockquote>
|
||
<h1>Foo</h1>
|
||
<p>bar
|
||
baz</p>
|
||
</blockquote>
|
||
.
|
||
|
||
A block quote can contain some lazy and some non-lazy
|
||
continuation lines:
|
||
|
||
.
|
||
> bar
|
||
baz
|
||
> foo
|
||
.
|
||
<blockquote>
|
||
<p>bar
|
||
baz
|
||
foo</p>
|
||
</blockquote>
|
||
.
|
||
|
||
Laziness only applies to lines that are continuations of
|
||
paragraphs. Lines containing characters or indentation that indicate
|
||
block structure cannot be lazy.
|
||
|
||
.
|
||
> foo
|
||
---
|
||
.
|
||
<blockquote>
|
||
<p>foo</p>
|
||
</blockquote>
|
||
<hr />
|
||
.
|
||
|
||
.
|
||
> - foo
|
||
- bar
|
||
.
|
||
<blockquote>
|
||
<ul>
|
||
<li>foo</li>
|
||
</ul>
|
||
</blockquote>
|
||
<ul>
|
||
<li>bar</li>
|
||
</ul>
|
||
.
|
||
|
||
.
|
||
> foo
|
||
bar
|
||
.
|
||
<blockquote>
|
||
<pre><code>foo
|
||
</code></pre>
|
||
</blockquote>
|
||
<pre><code>bar
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
> ```
|
||
foo
|
||
```
|
||
.
|
||
<blockquote>
|
||
<pre><code></code></pre>
|
||
</blockquote>
|
||
<p>foo</p>
|
||
<pre><code></code></pre>
|
||
.
|
||
|
||
A block quote can be empty:
|
||
|
||
.
|
||
>
|
||
.
|
||
<blockquote>
|
||
</blockquote>
|
||
.
|
||
|
||
.
|
||
>
|
||
>
|
||
>
|
||
.
|
||
<blockquote>
|
||
</blockquote>
|
||
.
|
||
|
||
A block quote can have initial or final blank lines:
|
||
|
||
.
|
||
>
|
||
> foo
|
||
>
|
||
.
|
||
<blockquote>
|
||
<p>foo</p>
|
||
</blockquote>
|
||
.
|
||
|
||
A blank line always separates block quotes:
|
||
|
||
.
|
||
> foo
|
||
|
||
> bar
|
||
.
|
||
<blockquote>
|
||
<p>foo</p>
|
||
</blockquote>
|
||
<blockquote>
|
||
<p>bar</p>
|
||
</blockquote>
|
||
.
|
||
|
||
(Most current Markdown implementations, including John Gruber's
|
||
original `Markdown.pl`, will parse this example as a single block quote
|
||
with two paragraphs. But it seems better to allow the author to decide
|
||
whether two block quotes or one are wanted.)
|
||
|
||
Consecutiveness means that if we put these block quotes together,
|
||
we get a single block quote:
|
||
|
||
.
|
||
> foo
|
||
> bar
|
||
.
|
||
<blockquote>
|
||
<p>foo
|
||
bar</p>
|
||
</blockquote>
|
||
.
|
||
|
||
To get a block quote with two paragraphs, use:
|
||
|
||
.
|
||
> foo
|
||
>
|
||
> bar
|
||
.
|
||
<blockquote>
|
||
<p>foo</p>
|
||
<p>bar</p>
|
||
</blockquote>
|
||
.
|
||
|
||
Block quotes can interrupt paragraphs:
|
||
|
||
.
|
||
foo
|
||
> bar
|
||
.
|
||
<p>foo</p>
|
||
<blockquote>
|
||
<p>bar</p>
|
||
</blockquote>
|
||
.
|
||
|
||
In general, blank lines are not needed before or after block
|
||
quotes:
|
||
|
||
.
|
||
> aaa
|
||
***
|
||
> bbb
|
||
.
|
||
<blockquote>
|
||
<p>aaa</p>
|
||
</blockquote>
|
||
<hr />
|
||
<blockquote>
|
||
<p>bbb</p>
|
||
</blockquote>
|
||
.
|
||
|
||
However, because of laziness, a blank line is needed between
|
||
a block quote and a following paragraph:
|
||
|
||
.
|
||
> bar
|
||
baz
|
||
.
|
||
<blockquote>
|
||
<p>bar
|
||
baz</p>
|
||
</blockquote>
|
||
.
|
||
|
||
.
|
||
> bar
|
||
|
||
baz
|
||
.
|
||
<blockquote>
|
||
<p>bar</p>
|
||
</blockquote>
|
||
<p>baz</p>
|
||
.
|
||
|
||
.
|
||
> bar
|
||
>
|
||
baz
|
||
.
|
||
<blockquote>
|
||
<p>bar</p>
|
||
</blockquote>
|
||
<p>baz</p>
|
||
.
|
||
|
||
It is a consequence of the Laziness rule that any number
|
||
of initial `>`s may be omitted on a continuation line of a
|
||
nested block quote:
|
||
|
||
.
|
||
> > > foo
|
||
bar
|
||
.
|
||
<blockquote>
|
||
<blockquote>
|
||
<blockquote>
|
||
<p>foo
|
||
bar</p>
|
||
</blockquote>
|
||
</blockquote>
|
||
</blockquote>
|
||
.
|
||
|
||
.
|
||
>>> foo
|
||
> bar
|
||
>>baz
|
||
.
|
||
<blockquote>
|
||
<blockquote>
|
||
<blockquote>
|
||
<p>foo
|
||
bar
|
||
baz</p>
|
||
</blockquote>
|
||
</blockquote>
|
||
</blockquote>
|
||
.
|
||
|
||
When including an indented code block in a block quote,
|
||
remember that the [block quote marker] includes
|
||
both the `>` and a following space. So *five spaces* are needed after
|
||
the `>`:
|
||
|
||
.
|
||
> code
|
||
|
||
> not code
|
||
.
|
||
<blockquote>
|
||
<pre><code>code
|
||
</code></pre>
|
||
</blockquote>
|
||
<blockquote>
|
||
<p>not code</p>
|
||
</blockquote>
|
||
.
|
||
|
||
|
||
## List items
|
||
|
||
A [list marker](@list-marker) is a
|
||
[bullet list marker] or an [ordered list marker].
|
||
|
||
A [bullet list marker](@bullet-list-marker)
|
||
is a `-`, `+`, or `*` character.
|
||
|
||
An [ordered list marker](@ordered-list-marker)
|
||
is a sequence of one of more digits (`0-9`), followed by either a
|
||
`.` character or a `)` character.
|
||
|
||
The following rules define [list items]:
|
||
|
||
1. **Basic case.** If a sequence of lines *Ls* constitute a sequence of
|
||
blocks *Bs* starting with a [non-space character] and not separated
|
||
from each other by more than one blank line, and *M* is a list
|
||
marker *M* of width *W* followed by 0 < *N* < 5 spaces, then the result
|
||
of prepending *M* and the following spaces to the first line of
|
||
*Ls*, and indenting subsequent lines of *Ls* by *W + N* spaces, is a
|
||
list item with *Bs* as its contents. The type of the list item
|
||
(bullet or ordered) is determined by the type of its list marker.
|
||
If the list item is ordered, then it is also assigned a start
|
||
number, based on the ordered list marker.
|
||
|
||
For example, let *Ls* be the lines
|
||
|
||
.
|
||
A paragraph
|
||
with two lines.
|
||
|
||
indented code
|
||
|
||
> A block quote.
|
||
.
|
||
<p>A paragraph
|
||
with two lines.</p>
|
||
<pre><code>indented code
|
||
</code></pre>
|
||
<blockquote>
|
||
<p>A block quote.</p>
|
||
</blockquote>
|
||
.
|
||
|
||
And let *M* be the marker `1.`, and *N* = 2. Then rule #1 says
|
||
that the following is an ordered list item with start number 1,
|
||
and the same contents as *Ls*:
|
||
|
||
.
|
||
1. A paragraph
|
||
with two lines.
|
||
|
||
indented code
|
||
|
||
> A block quote.
|
||
.
|
||
<ol>
|
||
<li>
|
||
<p>A paragraph
|
||
with two lines.</p>
|
||
<pre><code>indented code
|
||
</code></pre>
|
||
<blockquote>
|
||
<p>A block quote.</p>
|
||
</blockquote>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
The most important thing to notice is that the position of
|
||
the text after the list marker determines how much indentation
|
||
is needed in subsequent blocks in the list item. If the list
|
||
marker takes up two spaces, and there are three spaces between
|
||
the list marker and the next [non-space character], then blocks
|
||
must be indented five spaces in order to fall under the list
|
||
item.
|
||
|
||
Here are some examples showing how far content must be indented to be
|
||
put under the list item:
|
||
|
||
.
|
||
- one
|
||
|
||
two
|
||
.
|
||
<ul>
|
||
<li>one</li>
|
||
</ul>
|
||
<p>two</p>
|
||
.
|
||
|
||
.
|
||
- one
|
||
|
||
two
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>one</p>
|
||
<p>two</p>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
.
|
||
- one
|
||
|
||
two
|
||
.
|
||
<ul>
|
||
<li>one</li>
|
||
</ul>
|
||
<pre><code> two
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
- one
|
||
|
||
two
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>one</p>
|
||
<p>two</p>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
It is tempting to think of this in terms of columns: the continuation
|
||
blocks must be indented at least to the column of the first
|
||
[non-space character] after the list marker. However, that is not quite right.
|
||
The spaces after the list marker determine how much relative indentation
|
||
is needed. Which column this indentation reaches will depend on
|
||
how the list item is embedded in other constructions, as shown by
|
||
this example:
|
||
|
||
.
|
||
> > 1. one
|
||
>>
|
||
>> two
|
||
.
|
||
<blockquote>
|
||
<blockquote>
|
||
<ol>
|
||
<li>
|
||
<p>one</p>
|
||
<p>two</p>
|
||
</li>
|
||
</ol>
|
||
</blockquote>
|
||
</blockquote>
|
||
.
|
||
|
||
Here `two` occurs in the same column as the list marker `1.`,
|
||
but is actually contained in the list item, because there is
|
||
sufficent indentation after the last containing blockquote marker.
|
||
|
||
The converse is also possible. In the following example, the word `two`
|
||
occurs far to the right of the initial text of the list item, `one`, but
|
||
it is not considered part of the list item, because it is not indented
|
||
far enough past the blockquote marker:
|
||
|
||
.
|
||
>>- one
|
||
>>
|
||
> > two
|
||
.
|
||
<blockquote>
|
||
<blockquote>
|
||
<ul>
|
||
<li>one</li>
|
||
</ul>
|
||
<p>two</p>
|
||
</blockquote>
|
||
</blockquote>
|
||
.
|
||
|
||
A list item may not contain blocks that are separated by more than
|
||
one blank line. Thus, two blank lines will end a list, unless the
|
||
two blanks are contained in a [fenced code block].
|
||
|
||
.
|
||
- foo
|
||
|
||
bar
|
||
|
||
- foo
|
||
|
||
|
||
bar
|
||
|
||
- ```
|
||
foo
|
||
|
||
|
||
bar
|
||
```
|
||
|
||
- baz
|
||
|
||
+ ```
|
||
foo
|
||
|
||
|
||
bar
|
||
```
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>foo</p>
|
||
<p>bar</p>
|
||
</li>
|
||
<li>
|
||
<p>foo</p>
|
||
</li>
|
||
</ul>
|
||
<p>bar</p>
|
||
<ul>
|
||
<li>
|
||
<pre><code>foo
|
||
|
||
|
||
bar
|
||
</code></pre>
|
||
</li>
|
||
<li>
|
||
<p>baz</p>
|
||
<ul>
|
||
<li>
|
||
<pre><code>foo
|
||
|
||
|
||
bar
|
||
</code></pre>
|
||
</li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
A list item may contain any kind of block:
|
||
|
||
.
|
||
1. foo
|
||
|
||
```
|
||
bar
|
||
```
|
||
|
||
baz
|
||
|
||
> bam
|
||
.
|
||
<ol>
|
||
<li>
|
||
<p>foo</p>
|
||
<pre><code>bar
|
||
</code></pre>
|
||
<p>baz</p>
|
||
<blockquote>
|
||
<p>bam</p>
|
||
</blockquote>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
2. **Item starting with indented code.** If a sequence of lines *Ls*
|
||
constitute a sequence of blocks *Bs* starting with an indented code
|
||
block and not separated from each other by more than one blank line,
|
||
and *M* is a list marker *M* of width *W* followed by
|
||
one space, then the result of prepending *M* and the following
|
||
space to the first line of *Ls*, and indenting subsequent lines of
|
||
*Ls* by *W + 1* spaces, is a list item with *Bs* as its contents.
|
||
If a line is empty, then it need not be indented. The type of the
|
||
list item (bullet or ordered) is determined by the type of its list
|
||
marker. If the list item is ordered, then it is also assigned a
|
||
start number, based on the ordered list marker.
|
||
|
||
An indented code block will have to be indented four spaces beyond
|
||
the edge of the region where text will be included in the list item.
|
||
In the following case that is 6 spaces:
|
||
|
||
.
|
||
- foo
|
||
|
||
bar
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>foo</p>
|
||
<pre><code>bar
|
||
</code></pre>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
And in this case it is 11 spaces:
|
||
|
||
.
|
||
10. foo
|
||
|
||
bar
|
||
.
|
||
<ol start="10">
|
||
<li>
|
||
<p>foo</p>
|
||
<pre><code>bar
|
||
</code></pre>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
If the *first* block in the list item is an indented code block,
|
||
then by rule #2, the contents must be indented *one* space after the
|
||
list marker:
|
||
|
||
.
|
||
indented code
|
||
|
||
paragraph
|
||
|
||
more code
|
||
.
|
||
<pre><code>indented code
|
||
</code></pre>
|
||
<p>paragraph</p>
|
||
<pre><code>more code
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
1. indented code
|
||
|
||
paragraph
|
||
|
||
more code
|
||
.
|
||
<ol>
|
||
<li>
|
||
<pre><code>indented code
|
||
</code></pre>
|
||
<p>paragraph</p>
|
||
<pre><code>more code
|
||
</code></pre>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
Note that an additional space indent is interpreted as space
|
||
inside the code block:
|
||
|
||
.
|
||
1. indented code
|
||
|
||
paragraph
|
||
|
||
more code
|
||
.
|
||
<ol>
|
||
<li>
|
||
<pre><code> indented code
|
||
</code></pre>
|
||
<p>paragraph</p>
|
||
<pre><code>more code
|
||
</code></pre>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
Note that rules #1 and #2 only apply to two cases: (a) cases
|
||
in which the lines to be included in a list item begin with a
|
||
[non-space character], and (b) cases in which
|
||
they begin with an indented code
|
||
block. In a case like the following, where the first block begins with
|
||
a three-space indent, the rules do not allow us to form a list item by
|
||
indenting the whole thing and prepending a list marker:
|
||
|
||
.
|
||
foo
|
||
|
||
bar
|
||
.
|
||
<p>foo</p>
|
||
<p>bar</p>
|
||
.
|
||
|
||
.
|
||
- foo
|
||
|
||
bar
|
||
.
|
||
<ul>
|
||
<li>foo</li>
|
||
</ul>
|
||
<p>bar</p>
|
||
.
|
||
|
||
This is not a significant restriction, because when a block begins
|
||
with 1-3 spaces indent, the indentation can always be removed without
|
||
a change in interpretation, allowing rule #1 to be applied. So, in
|
||
the above case:
|
||
|
||
.
|
||
- foo
|
||
|
||
bar
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>foo</p>
|
||
<p>bar</p>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
3. **Empty list item.** A [list marker] followed by a
|
||
line containing only [whitespace] is a list item with no contents.
|
||
|
||
Here is an empty bullet list item:
|
||
|
||
.
|
||
- foo
|
||
-
|
||
- bar
|
||
.
|
||
<ul>
|
||
<li>foo</li>
|
||
<li></li>
|
||
<li>bar</li>
|
||
</ul>
|
||
.
|
||
|
||
It does not matter whether there are spaces following the [list marker]:
|
||
|
||
.
|
||
- foo
|
||
-
|
||
- bar
|
||
.
|
||
<ul>
|
||
<li>foo</li>
|
||
<li></li>
|
||
<li>bar</li>
|
||
</ul>
|
||
.
|
||
|
||
Here is an empty ordered list item:
|
||
|
||
.
|
||
1. foo
|
||
2.
|
||
3. bar
|
||
.
|
||
<ol>
|
||
<li>foo</li>
|
||
<li></li>
|
||
<li>bar</li>
|
||
</ol>
|
||
.
|
||
|
||
A list may start or end with an empty list item:
|
||
|
||
.
|
||
*
|
||
.
|
||
<ul>
|
||
<li></li>
|
||
</ul>
|
||
.
|
||
|
||
4. **Indentation.** If a sequence of lines *Ls* constitutes a list item
|
||
according to rule #1, #2, or #3, then the result of indenting each line
|
||
of *L* by 1-3 spaces (the same for each line) also constitutes a
|
||
list item with the same contents and attributes. If a line is
|
||
empty, then it need not be indented.
|
||
|
||
Indented one space:
|
||
|
||
.
|
||
1. A paragraph
|
||
with two lines.
|
||
|
||
indented code
|
||
|
||
> A block quote.
|
||
.
|
||
<ol>
|
||
<li>
|
||
<p>A paragraph
|
||
with two lines.</p>
|
||
<pre><code>indented code
|
||
</code></pre>
|
||
<blockquote>
|
||
<p>A block quote.</p>
|
||
</blockquote>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
Indented two spaces:
|
||
|
||
.
|
||
1. A paragraph
|
||
with two lines.
|
||
|
||
indented code
|
||
|
||
> A block quote.
|
||
.
|
||
<ol>
|
||
<li>
|
||
<p>A paragraph
|
||
with two lines.</p>
|
||
<pre><code>indented code
|
||
</code></pre>
|
||
<blockquote>
|
||
<p>A block quote.</p>
|
||
</blockquote>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
Indented three spaces:
|
||
|
||
.
|
||
1. A paragraph
|
||
with two lines.
|
||
|
||
indented code
|
||
|
||
> A block quote.
|
||
.
|
||
<ol>
|
||
<li>
|
||
<p>A paragraph
|
||
with two lines.</p>
|
||
<pre><code>indented code
|
||
</code></pre>
|
||
<blockquote>
|
||
<p>A block quote.</p>
|
||
</blockquote>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
Four spaces indent gives a code block:
|
||
|
||
.
|
||
1. A paragraph
|
||
with two lines.
|
||
|
||
indented code
|
||
|
||
> A block quote.
|
||
.
|
||
<pre><code>1. A paragraph
|
||
with two lines.
|
||
|
||
indented code
|
||
|
||
> A block quote.
|
||
</code></pre>
|
||
.
|
||
|
||
|
||
5. **Laziness.** If a string of lines *Ls* constitute a [list
|
||
item](#list-items) with contents *Bs*, then the result of deleting
|
||
some or all of the indentation from one or more lines in which the
|
||
next [non-space character] after the indentation is
|
||
[paragraph continuation text] is a
|
||
list item with the same contents and attributes. The unindented
|
||
lines are called
|
||
[lazy continuation line](@lazy-continuation-line)s.
|
||
|
||
Here is an example with [lazy continuation line]s:
|
||
|
||
.
|
||
1. A paragraph
|
||
with two lines.
|
||
|
||
indented code
|
||
|
||
> A block quote.
|
||
.
|
||
<ol>
|
||
<li>
|
||
<p>A paragraph
|
||
with two lines.</p>
|
||
<pre><code>indented code
|
||
</code></pre>
|
||
<blockquote>
|
||
<p>A block quote.</p>
|
||
</blockquote>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
Indentation can be partially deleted:
|
||
|
||
.
|
||
1. A paragraph
|
||
with two lines.
|
||
.
|
||
<ol>
|
||
<li>A paragraph
|
||
with two lines.</li>
|
||
</ol>
|
||
.
|
||
|
||
These examples show how laziness can work in nested structures:
|
||
|
||
.
|
||
> 1. > Blockquote
|
||
continued here.
|
||
.
|
||
<blockquote>
|
||
<ol>
|
||
<li>
|
||
<blockquote>
|
||
<p>Blockquote
|
||
continued here.</p>
|
||
</blockquote>
|
||
</li>
|
||
</ol>
|
||
</blockquote>
|
||
.
|
||
|
||
.
|
||
> 1. > Blockquote
|
||
> continued here.
|
||
.
|
||
<blockquote>
|
||
<ol>
|
||
<li>
|
||
<blockquote>
|
||
<p>Blockquote
|
||
continued here.</p>
|
||
</blockquote>
|
||
</li>
|
||
</ol>
|
||
</blockquote>
|
||
.
|
||
|
||
|
||
6. **That's all.** Nothing that is not counted as a list item by rules
|
||
#1--5 counts as a [list item](#list-items).
|
||
|
||
The rules for sublists follow from the general rules above. A sublist
|
||
must be indented the same number of spaces a paragraph would need to be
|
||
in order to be included in the list item.
|
||
|
||
So, in this case we need two spaces indent:
|
||
|
||
.
|
||
- foo
|
||
- bar
|
||
- baz
|
||
.
|
||
<ul>
|
||
<li>foo
|
||
<ul>
|
||
<li>bar
|
||
<ul>
|
||
<li>baz</li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
One is not enough:
|
||
|
||
.
|
||
- foo
|
||
- bar
|
||
- baz
|
||
.
|
||
<ul>
|
||
<li>foo</li>
|
||
<li>bar</li>
|
||
<li>baz</li>
|
||
</ul>
|
||
.
|
||
|
||
Here we need four, because the list marker is wider:
|
||
|
||
.
|
||
10) foo
|
||
- bar
|
||
.
|
||
<ol start="10">
|
||
<li>foo
|
||
<ul>
|
||
<li>bar</li>
|
||
</ul>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
Three is not enough:
|
||
|
||
.
|
||
10) foo
|
||
- bar
|
||
.
|
||
<ol start="10">
|
||
<li>foo</li>
|
||
</ol>
|
||
<ul>
|
||
<li>bar</li>
|
||
</ul>
|
||
.
|
||
|
||
A list may be the first block in a list item:
|
||
|
||
.
|
||
- - foo
|
||
.
|
||
<ul>
|
||
<li>
|
||
<ul>
|
||
<li>foo</li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
.
|
||
1. - 2. foo
|
||
.
|
||
<ol>
|
||
<li>
|
||
<ul>
|
||
<li>
|
||
<ol start="2">
|
||
<li>foo</li>
|
||
</ol>
|
||
</li>
|
||
</ul>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
A list item can contain a header:
|
||
|
||
.
|
||
- # Foo
|
||
- Bar
|
||
---
|
||
baz
|
||
.
|
||
<ul>
|
||
<li>
|
||
<h1>Foo</h1>
|
||
</li>
|
||
<li>
|
||
<h2>Bar</h2>
|
||
baz</li>
|
||
</ul>
|
||
.
|
||
|
||
### Motivation
|
||
|
||
John Gruber's Markdown spec says the following about list items:
|
||
|
||
1. "List markers typically start at the left margin, but may be indented
|
||
by up to three spaces. List markers must be followed by one or more
|
||
spaces or a tab."
|
||
|
||
2. "To make lists look nice, you can wrap items with hanging indents....
|
||
But if you don't want to, you don't have to."
|
||
|
||
3. "List items may consist of multiple paragraphs. Each subsequent
|
||
paragraph in a list item must be indented by either 4 spaces or one
|
||
tab."
|
||
|
||
4. "It looks nice if you indent every line of the subsequent paragraphs,
|
||
but here again, Markdown will allow you to be lazy."
|
||
|
||
5. "To put a blockquote within a list item, the blockquote's `>`
|
||
delimiters need to be indented."
|
||
|
||
6. "To put a code block within a list item, the code block needs to be
|
||
indented twice — 8 spaces or two tabs."
|
||
|
||
These rules specify that a paragraph under a list item must be indented
|
||
four spaces (presumably, from the left margin, rather than the start of
|
||
the list marker, but this is not said), and that code under a list item
|
||
must be indented eight spaces instead of the usual four. They also say
|
||
that a block quote must be indented, but not by how much; however, the
|
||
example given has four spaces indentation. Although nothing is said
|
||
about other kinds of block-level content, it is certainly reasonable to
|
||
infer that *all* block elements under a list item, including other
|
||
lists, must be indented four spaces. This principle has been called the
|
||
*four-space rule*.
|
||
|
||
The four-space rule is clear and principled, and if the reference
|
||
implementation `Markdown.pl` had followed it, it probably would have
|
||
become the standard. However, `Markdown.pl` allowed paragraphs and
|
||
sublists to start with only two spaces indentation, at least on the
|
||
outer level. Worse, its behavior was inconsistent: a sublist of an
|
||
outer-level list needed two spaces indentation, but a sublist of this
|
||
sublist needed three spaces. It is not surprising, then, that different
|
||
implementations of Markdown have developed very different rules for
|
||
determining what comes under a list item. (Pandoc and python-Markdown,
|
||
for example, stuck with Gruber's syntax description and the four-space
|
||
rule, while discount, redcarpet, marked, PHP Markdown, and others
|
||
followed `Markdown.pl`'s behavior more closely.)
|
||
|
||
Unfortunately, given the divergences between implementations, there
|
||
is no way to give a spec for list items that will be guaranteed not
|
||
to break any existing documents. However, the spec given here should
|
||
correctly handle lists formatted with either the four-space rule or
|
||
the more forgiving `Markdown.pl` behavior, provided they are laid out
|
||
in a way that is natural for a human to read.
|
||
|
||
The strategy here is to let the width and indentation of the list marker
|
||
determine the indentation necessary for blocks to fall under the list
|
||
item, rather than having a fixed and arbitrary number. The writer can
|
||
think of the body of the list item as a unit which gets indented to the
|
||
right enough to fit the list marker (and any indentation on the list
|
||
marker). (The laziness rule, #5, then allows continuation lines to be
|
||
unindented if needed.)
|
||
|
||
This rule is superior, we claim, to any rule requiring a fixed level of
|
||
indentation from the margin. The four-space rule is clear but
|
||
unnatural. It is quite unintuitive that
|
||
|
||
``` markdown
|
||
- foo
|
||
|
||
bar
|
||
|
||
- baz
|
||
```
|
||
|
||
should be parsed as two lists with an intervening paragraph,
|
||
|
||
``` html
|
||
<ul>
|
||
<li>foo</li>
|
||
</ul>
|
||
<p>bar</p>
|
||
<ul>
|
||
<li>baz</li>
|
||
</ul>
|
||
```
|
||
|
||
as the four-space rule demands, rather than a single list,
|
||
|
||
``` html
|
||
<ul>
|
||
<li>
|
||
<p>foo</p>
|
||
<p>bar</p>
|
||
<ul>
|
||
<li>baz</li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
```
|
||
|
||
The choice of four spaces is arbitrary. It can be learned, but it is
|
||
not likely to be guessed, and it trips up beginners regularly.
|
||
|
||
Would it help to adopt a two-space rule? The problem is that such
|
||
a rule, together with the rule allowing 1--3 spaces indentation of the
|
||
initial list marker, allows text that is indented *less than* the
|
||
original list marker to be included in the list item. For example,
|
||
`Markdown.pl` parses
|
||
|
||
``` markdown
|
||
- one
|
||
|
||
two
|
||
```
|
||
|
||
as a single list item, with `two` a continuation paragraph:
|
||
|
||
``` html
|
||
<ul>
|
||
<li>
|
||
<p>one</p>
|
||
<p>two</p>
|
||
</li>
|
||
</ul>
|
||
```
|
||
|
||
and similarly
|
||
|
||
``` markdown
|
||
> - one
|
||
>
|
||
> two
|
||
```
|
||
|
||
as
|
||
|
||
``` html
|
||
<blockquote>
|
||
<ul>
|
||
<li>
|
||
<p>one</p>
|
||
<p>two</p>
|
||
</li>
|
||
</ul>
|
||
</blockquote>
|
||
```
|
||
|
||
This is extremely unintuitive.
|
||
|
||
Rather than requiring a fixed indent from the margin, we could require
|
||
a fixed indent (say, two spaces, or even one space) from the list marker (which
|
||
may itself be indented). This proposal would remove the last anomaly
|
||
discussed. Unlike the spec presented above, it would count the following
|
||
as a list item with a subparagraph, even though the paragraph `bar`
|
||
is not indented as far as the first paragraph `foo`:
|
||
|
||
``` markdown
|
||
10. foo
|
||
|
||
bar
|
||
```
|
||
|
||
Arguably this text does read like a list item with `bar` as a subparagraph,
|
||
which may count in favor of the proposal. However, on this proposal indented
|
||
code would have to be indented six spaces after the list marker. And this
|
||
would break a lot of existing Markdown, which has the pattern:
|
||
|
||
``` markdown
|
||
1. foo
|
||
|
||
indented code
|
||
```
|
||
|
||
where the code is indented eight spaces. The spec above, by contrast, will
|
||
parse this text as expected, since the code block's indentation is measured
|
||
from the beginning of `foo`.
|
||
|
||
The one case that needs special treatment is a list item that *starts*
|
||
with indented code. How much indentation is required in that case, since
|
||
we don't have a "first paragraph" to measure from? Rule #2 simply stipulates
|
||
that in such cases, we require one space indentation from the list marker
|
||
(and then the normal four spaces for the indented code). This will match the
|
||
four-space rule in cases where the list marker plus its initial indentation
|
||
takes four spaces (a common case), but diverge in other cases.
|
||
|
||
## Lists
|
||
|
||
A [list](@list) is a sequence of one or more
|
||
list items [of the same type]. The list items
|
||
may be separated by single [blank lines], but two
|
||
blank lines end all containing lists.
|
||
|
||
Two list items are [of the same type](@of-the-same-type)
|
||
if they begin with a [list marker] of the same type.
|
||
Two list markers are of the
|
||
same type if (a) they are bullet list markers using the same character
|
||
(`-`, `+`, or `*`) or (b) they are ordered list numbers with the same
|
||
delimiter (either `.` or `)`).
|
||
|
||
A list is an [ordered list](@ordered-list)
|
||
if its constituent list items begin with
|
||
[ordered list marker]s, and a
|
||
[bullet list](@bullet-list) if its constituent list
|
||
items begin with [bullet list marker]s.
|
||
|
||
The [start number](@start-number)
|
||
of an [ordered list] is determined by the list number of
|
||
its initial list item. The numbers of subsequent list items are
|
||
disregarded.
|
||
|
||
A list is [loose](@loose) if it any of its constituent
|
||
list items are separated by blank lines, or if any of its constituent
|
||
list items directly contain two block-level elements with a blank line
|
||
between them. Otherwise a list is [tight](@tight).
|
||
(The difference in HTML output is that paragraphs in a loose list are
|
||
wrapped in `<p>` tags, while paragraphs in a tight list are not.)
|
||
|
||
Changing the bullet or ordered list delimiter starts a new list:
|
||
|
||
.
|
||
- foo
|
||
- bar
|
||
+ baz
|
||
.
|
||
<ul>
|
||
<li>foo</li>
|
||
<li>bar</li>
|
||
</ul>
|
||
<ul>
|
||
<li>baz</li>
|
||
</ul>
|
||
.
|
||
|
||
.
|
||
1. foo
|
||
2. bar
|
||
3) baz
|
||
.
|
||
<ol>
|
||
<li>foo</li>
|
||
<li>bar</li>
|
||
</ol>
|
||
<ol start="3">
|
||
<li>baz</li>
|
||
</ol>
|
||
.
|
||
|
||
In CommonMark, a list can interrupt a paragraph. That is,
|
||
no blank line is needed to separate a paragraph from a following
|
||
list:
|
||
|
||
.
|
||
Foo
|
||
- bar
|
||
- baz
|
||
.
|
||
<p>Foo</p>
|
||
<ul>
|
||
<li>bar</li>
|
||
<li>baz</li>
|
||
</ul>
|
||
.
|
||
|
||
`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.
|
||
.
|
||
<p>The number of windows in my house is</p>
|
||
<ol start="14">
|
||
<li>The number of doors is 6.</li>
|
||
</ol>
|
||
.
|
||
|
||
Oddly, `Markdown.pl` *does* allow a blockquote to interrupt a paragraph,
|
||
even though the same considerations might apply. We think that the two
|
||
cases should be treated the same. Here are two reasons for allowing
|
||
lists to interrupt paragraphs:
|
||
|
||
First, it is natural and not uncommon for people to start lists without
|
||
blank lines:
|
||
|
||
I need to buy
|
||
- new shoes
|
||
- a coat
|
||
- a plane ticket
|
||
|
||
Second, we are attracted to a
|
||
|
||
> [principle of uniformity](@principle-of-uniformity):
|
||
> if a chunk of text has a certain
|
||
> meaning, it will continue to have the same meaning when put into a
|
||
> container block (such as a list item or blockquote).
|
||
|
||
(Indeed, the spec for [list items] and [block quotes] presupposes
|
||
this principle.) This principle implies that if
|
||
|
||
* I need to buy
|
||
- new shoes
|
||
- a coat
|
||
- a plane ticket
|
||
|
||
is a list item containing a paragraph followed by a nested sublist,
|
||
as all Markdown implementations agree it is (though the paragraph
|
||
may be rendered without `<p>` tags, since the list is "tight"),
|
||
then
|
||
|
||
I need to buy
|
||
- new shoes
|
||
- a coat
|
||
- a plane ticket
|
||
|
||
by itself should be a paragraph followed by a nested sublist.
|
||
|
||
Our adherence to the [principle of uniformity]
|
||
thus inclines us to think that there are two coherent packages:
|
||
|
||
1. Require blank lines before *all* lists and blockquotes,
|
||
including lists that occur as sublists inside other list items.
|
||
|
||
2. Require blank lines in none of these places.
|
||
|
||
[reStructuredText](http://docutils.sourceforge.net/rst.html) takes
|
||
the first approach, for which there is much to be said. But the second
|
||
seems more consistent with established practice with Markdown.
|
||
|
||
There can be blank lines between items, but two blank lines end
|
||
a list:
|
||
|
||
.
|
||
- foo
|
||
|
||
- bar
|
||
|
||
|
||
- baz
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>foo</p>
|
||
</li>
|
||
<li>
|
||
<p>bar</p>
|
||
</li>
|
||
</ul>
|
||
<ul>
|
||
<li>baz</li>
|
||
</ul>
|
||
.
|
||
|
||
As illustrated above in the section on [list items],
|
||
two blank lines between blocks *within* a list item will also end a
|
||
list:
|
||
|
||
.
|
||
- foo
|
||
|
||
|
||
bar
|
||
- baz
|
||
.
|
||
<ul>
|
||
<li>foo</li>
|
||
</ul>
|
||
<p>bar</p>
|
||
<ul>
|
||
<li>baz</li>
|
||
</ul>
|
||
.
|
||
|
||
Indeed, two blank lines will end *all* containing lists:
|
||
|
||
.
|
||
- foo
|
||
- bar
|
||
- baz
|
||
|
||
|
||
bim
|
||
.
|
||
<ul>
|
||
<li>foo
|
||
<ul>
|
||
<li>bar
|
||
<ul>
|
||
<li>baz</li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
<pre><code> bim
|
||
</code></pre>
|
||
.
|
||
|
||
Thus, two blank lines can be used to separate consecutive lists of
|
||
the same type, or to separate a list from an indented code block
|
||
that would otherwise be parsed as a subparagraph of the final list
|
||
item:
|
||
|
||
.
|
||
- foo
|
||
- bar
|
||
|
||
|
||
- baz
|
||
- bim
|
||
.
|
||
<ul>
|
||
<li>foo</li>
|
||
<li>bar</li>
|
||
</ul>
|
||
<ul>
|
||
<li>baz</li>
|
||
<li>bim</li>
|
||
</ul>
|
||
.
|
||
|
||
.
|
||
- foo
|
||
|
||
notcode
|
||
|
||
- foo
|
||
|
||
|
||
code
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>foo</p>
|
||
<p>notcode</p>
|
||
</li>
|
||
<li>
|
||
<p>foo</p>
|
||
</li>
|
||
</ul>
|
||
<pre><code>code
|
||
</code></pre>
|
||
.
|
||
|
||
List items need not be indented to the same level. The following
|
||
list items will be treated as items at the same list level,
|
||
since none is indented enough to belong to the previous list
|
||
item:
|
||
|
||
.
|
||
- a
|
||
- b
|
||
- c
|
||
- d
|
||
- e
|
||
- f
|
||
- g
|
||
.
|
||
<ul>
|
||
<li>a</li>
|
||
<li>b</li>
|
||
<li>c</li>
|
||
<li>d</li>
|
||
<li>e</li>
|
||
<li>f</li>
|
||
<li>g</li>
|
||
</ul>
|
||
.
|
||
|
||
This is a loose list, because there is a blank line between
|
||
two of the list items:
|
||
|
||
.
|
||
- a
|
||
- b
|
||
|
||
- c
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>a</p>
|
||
</li>
|
||
<li>
|
||
<p>b</p>
|
||
</li>
|
||
<li>
|
||
<p>c</p>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
So is this, with a empty second item:
|
||
|
||
.
|
||
* a
|
||
*
|
||
|
||
* c
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>a</p>
|
||
</li>
|
||
<li></li>
|
||
<li>
|
||
<p>c</p>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
These are loose lists, even though there is no space between the items,
|
||
because one of the items directly contains two block-level elements
|
||
with a blank line between them:
|
||
|
||
.
|
||
- a
|
||
- b
|
||
|
||
c
|
||
- d
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>a</p>
|
||
</li>
|
||
<li>
|
||
<p>b</p>
|
||
<p>c</p>
|
||
</li>
|
||
<li>
|
||
<p>d</p>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
.
|
||
- a
|
||
- b
|
||
|
||
[ref]: /url
|
||
- d
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>a</p>
|
||
</li>
|
||
<li>
|
||
<p>b</p>
|
||
</li>
|
||
<li>
|
||
<p>d</p>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
This is a tight list, because the blank lines are in a code block:
|
||
|
||
.
|
||
- a
|
||
- ```
|
||
b
|
||
|
||
|
||
```
|
||
- c
|
||
.
|
||
<ul>
|
||
<li>a</li>
|
||
<li>
|
||
<pre><code>b
|
||
|
||
|
||
</code></pre>
|
||
</li>
|
||
<li>c</li>
|
||
</ul>
|
||
.
|
||
|
||
This is a tight list, because the blank line is between two
|
||
paragraphs of a sublist. So the sublist is loose while
|
||
the outer list is tight:
|
||
|
||
.
|
||
- a
|
||
- b
|
||
|
||
c
|
||
- d
|
||
.
|
||
<ul>
|
||
<li>a
|
||
<ul>
|
||
<li>
|
||
<p>b</p>
|
||
<p>c</p>
|
||
</li>
|
||
</ul>
|
||
</li>
|
||
<li>d</li>
|
||
</ul>
|
||
.
|
||
|
||
This is a tight list, because the blank line is inside the
|
||
block quote:
|
||
|
||
.
|
||
* a
|
||
> b
|
||
>
|
||
* c
|
||
.
|
||
<ul>
|
||
<li>a
|
||
<blockquote>
|
||
<p>b</p>
|
||
</blockquote>
|
||
</li>
|
||
<li>c</li>
|
||
</ul>
|
||
.
|
||
|
||
This list is tight, because the consecutive block elements
|
||
are not separated by blank lines:
|
||
|
||
.
|
||
- a
|
||
> b
|
||
```
|
||
c
|
||
```
|
||
- d
|
||
.
|
||
<ul>
|
||
<li>a
|
||
<blockquote>
|
||
<p>b</p>
|
||
</blockquote>
|
||
<pre><code>c
|
||
</code></pre>
|
||
</li>
|
||
<li>d</li>
|
||
</ul>
|
||
.
|
||
|
||
A single-paragraph list is tight:
|
||
|
||
.
|
||
- a
|
||
.
|
||
<ul>
|
||
<li>a</li>
|
||
</ul>
|
||
.
|
||
|
||
.
|
||
- a
|
||
- b
|
||
.
|
||
<ul>
|
||
<li>a
|
||
<ul>
|
||
<li>b</li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
This list is loose, because of the blank line between the
|
||
two block elements in the list item:
|
||
|
||
.
|
||
1. ```
|
||
foo
|
||
```
|
||
|
||
bar
|
||
.
|
||
<ol>
|
||
<li>
|
||
<pre><code>foo
|
||
</code></pre>
|
||
<p>bar</p>
|
||
</li>
|
||
</ol>
|
||
.
|
||
|
||
Here the outer list is loose, the inner list tight:
|
||
|
||
.
|
||
* foo
|
||
* bar
|
||
|
||
baz
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>foo</p>
|
||
<ul>
|
||
<li>bar</li>
|
||
</ul>
|
||
<p>baz</p>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
.
|
||
- a
|
||
- b
|
||
- c
|
||
|
||
- d
|
||
- e
|
||
- f
|
||
.
|
||
<ul>
|
||
<li>
|
||
<p>a</p>
|
||
<ul>
|
||
<li>b</li>
|
||
<li>c</li>
|
||
</ul>
|
||
</li>
|
||
<li>
|
||
<p>d</p>
|
||
<ul>
|
||
<li>e</li>
|
||
<li>f</li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
.
|
||
|
||
# Inlines
|
||
|
||
Inlines are parsed sequentially from the beginning of the character
|
||
stream to the end (left to right, in left-to-right languages).
|
||
Thus, for example, in
|
||
|
||
.
|
||
`hi`lo`
|
||
.
|
||
<p><code>hi</code>lo`</p>
|
||
.
|
||
|
||
`hi` is parsed as code, leaving the backtick at the end as a literal
|
||
backtick.
|
||
|
||
## Backslash escapes
|
||
|
||
Any ASCII punctuation character may be backslash-escaped:
|
||
|
||
.
|
||
\!\"\#\$\%\&\'\(\)\*\+\,\-\.\/\:\;\<\=\>\?\@\[\\\]\^\_\`\{\|\}\~
|
||
.
|
||
<p>!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~</p>
|
||
.
|
||
|
||
Backslashes before other characters are treated as literal
|
||
backslashes:
|
||
|
||
.
|
||
\→\A\a\ \3\φ\«
|
||
.
|
||
<p>\ \A\a\ \3\φ\«</p>
|
||
.
|
||
|
||
Escaped characters are treated as regular characters and do
|
||
not have their usual Markdown meanings:
|
||
|
||
.
|
||
\*not emphasized*
|
||
\<br/> not a tag
|
||
\[not a link](/foo)
|
||
\`not code`
|
||
1\. not a list
|
||
\* not a list
|
||
\# not a header
|
||
\[foo]: /url "not a reference"
|
||
.
|
||
<p>*not emphasized*
|
||
<br/> not a tag
|
||
[not a link](/foo)
|
||
`not code`
|
||
1. not a list
|
||
* not a list
|
||
# not a header
|
||
[foo]: /url "not a reference"</p>
|
||
.
|
||
|
||
If a backslash is itself escaped, the following character is not:
|
||
|
||
.
|
||
\\*emphasis*
|
||
.
|
||
<p>\<em>emphasis</em></p>
|
||
.
|
||
|
||
A backslash at the end of the line is a [hard line break]:
|
||
|
||
.
|
||
foo\
|
||
bar
|
||
.
|
||
<p>foo<br />
|
||
bar</p>
|
||
.
|
||
|
||
Backslash escapes do not work in code blocks, code spans, autolinks, or
|
||
raw HTML:
|
||
|
||
.
|
||
`` \[\` ``
|
||
.
|
||
<p><code>\[\`</code></p>
|
||
.
|
||
|
||
.
|
||
\[\]
|
||
.
|
||
<pre><code>\[\]
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
~~~
|
||
\[\]
|
||
~~~
|
||
.
|
||
<pre><code>\[\]
|
||
</code></pre>
|
||
.
|
||
|
||
.
|
||
<http://example.com?find=\*>
|
||
.
|
||
<p><a href="http://example.com?find=%5C*">http://example.com?find=\*</a></p>
|
||
.
|
||
|
||
.
|
||
<a href="/bar\/)">
|
||
.
|
||
<p><a href="/bar\/)"></p>
|
||
.
|
||
|
||
But they work in all other contexts, including URLs and link titles,
|
||
link references, and [info string]s in [fenced code block]s:
|
||
|
||
.
|
||
[foo](/bar\* "ti\*tle")
|
||
.
|
||
<p><a href="/bar*" title="ti*tle">foo</a></p>
|
||
.
|
||
|
||
.
|
||
[foo]
|
||
|
||
[foo]: /bar\* "ti\*tle"
|
||
.
|
||
<p><a href="/bar*" title="ti*tle">foo</a></p>
|
||
.
|
||
|
||
.
|
||
``` foo\+bar
|
||
foo
|
||
```
|
||
.
|
||
<pre><code class="language-foo+bar">foo
|
||
</code></pre>
|
||
.
|
||
|
||
|
||
## Entities
|
||
|
||
With the goal of making this standard as HTML-agnostic as possible, all
|
||
valid HTML entities (except in code blocks and code spans)
|
||
are recognized as such and converted into unicode characters before
|
||
they are stored in the AST. This means that renderers to formats other
|
||
than HTML need not be HTML-entity aware. HTML renderers may either escape
|
||
unicode characters as entities or leave them as they are. (However,
|
||
`"`, `&`, `<`, and `>` must always be rendered as entities.)
|
||
|
||
[Named entities](@name-entities) consist of `&`
|
||
+ any of the valid HTML5 entity names + `;`. The
|
||
[following document](https://html.spec.whatwg.org/multipage/entities.json)
|
||
is used as an authoritative source of the valid entity names and their
|
||
corresponding codepoints.
|
||
|
||
.
|
||
& © Æ Ď ¾ ℋ ⅆ ∲
|
||
.
|
||
<p> & © Æ Ď ¾ ℋ ⅆ ∲</p>
|
||
.
|
||
|
||
[Decimal entities](@decimal-entities)
|
||
consist of `&#` + a string of 1--8 arabic digits + `;`. Again, these
|
||
entities need to be recognised and tranformed into their corresponding
|
||
UTF8 codepoints. Invalid Unicode codepoints will be written as the
|
||
"unknown codepoint" character (`0xFFFD`)
|
||
|
||
.
|
||
# Ӓ Ϡ �
|
||
.
|
||
<p># Ӓ Ϡ <20></p>
|
||
.
|
||
|
||
[Hexadecimal entities](@hexadecimal-entities)
|
||
consist of `&#` + either `X` or `x` + a string of 1-8 hexadecimal digits
|
||
+ `;`. They will also be parsed and turned into their corresponding UTF8 values in the AST.
|
||
|
||
.
|
||
" ആ ಫ
|
||
.
|
||
<p>" ആ ಫ</p>
|
||
.
|
||
|
||
Here are some nonentities:
|
||
|
||
.
|
||
  &x; &#; &#x; &ThisIsWayTooLongToBeAnEntityIsntIt; &hi?;
|
||
.
|
||
<p>&nbsp &x; &#; &#x; &ThisIsWayTooLongToBeAnEntityIsntIt; &hi?;</p>
|
||
.
|
||
|
||
Although HTML5 does accept some entities without a trailing semicolon
|
||
(such as `©`), these are not recognized as entities here, because it
|
||
makes the grammar too ambiguous:
|
||
|
||
.
|
||
©
|
||
.
|
||
<p>&copy</p>
|
||
.
|
||
|
||
Strings that are not on the list of HTML5 named entities are not
|
||
recognized as entities either:
|
||
|
||
.
|
||
&MadeUpEntity;
|
||
.
|
||
<p>&MadeUpEntity;</p>
|
||
.
|
||
|
||
Entities are recognized in any context besides code spans or
|
||
code blocks, including raw HTML, URLs, [link title]s, and
|
||
[fenced code block] [info string]s:
|
||
|
||
.
|
||
<a href="öö.html">
|
||
.
|
||
<p><a href="öö.html"></p>
|
||
.
|
||
|
||
.
|
||
[foo](/föö "föö")
|
||
.
|
||
<p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p>
|
||
.
|
||
|
||
.
|
||
[foo]
|
||
|
||
[foo]: /föö "föö"
|
||
.
|
||
<p><a href="/f%C3%B6%C3%B6" title="föö">foo</a></p>
|
||
.
|
||
|
||
.
|
||
``` föö
|
||
foo
|
||
```
|
||
.
|
||
<pre><code class="language-föö">foo
|
||
</code></pre>
|
||
.
|
||
|
||
Entities are treated as literal text in code spans and code blocks:
|
||
|
||
.
|
||
`föö`
|
||
.
|
||
<p><code>f&ouml;&ouml;</code></p>
|
||
.
|
||
|
||
.
|
||
föfö
|
||
.
|
||
<pre><code>f&ouml;f&ouml;
|
||
</code></pre>
|
||
.
|
||
|
||
## Code spans
|
||
|
||
A [backtick string](@backtick-string)
|
||
is a string of one or more backtick characters (`` ` ``) that is neither
|
||
preceded nor followed by a backtick.
|
||
|
||
A [code span](@code-span) begins with a backtick string and ends with
|
||
a backtick string of equal length. The contents of the code span are
|
||
the characters between the two backtick strings, with leading and
|
||
trailing spaces and [line ending]s removed, and
|
||
[whitespace] collapsed to single spaces.
|
||
|
||
This is a simple code span:
|
||
|
||
.
|
||
`foo`
|
||
.
|
||
<p><code>foo</code></p>
|
||
.
|
||
|
||
Here two backticks are used, because the code contains a backtick.
|
||
This example also illustrates stripping of leading and trailing spaces:
|
||
|
||
.
|
||
`` foo ` bar ``
|
||
.
|
||
<p><code>foo ` bar</code></p>
|
||
.
|
||
|
||
This example shows the motivation for stripping leading and trailing
|
||
spaces:
|
||
|
||
.
|
||
` `` `
|
||
.
|
||
<p><code>``</code></p>
|
||
.
|
||
|
||
[Line ending]s are treated like spaces:
|
||
|
||
.
|
||
``
|
||
foo
|
||
``
|
||
.
|
||
<p><code>foo</code></p>
|
||
.
|
||
|
||
Interior spaces and [line ending]s are collapsed into
|
||
single spaces, just as they would be by a browser:
|
||
|
||
.
|
||
`foo bar
|
||
baz`
|
||
.
|
||
<p><code>foo bar baz</code></p>
|
||
.
|
||
|
||
Q: Why not just leave the spaces, since browsers will collapse them
|
||
anyway? A: Because we might be targeting a non-HTML format, and we
|
||
shouldn't rely on HTML-specific rendering assumptions.
|
||
|
||
(Existing implementations differ in their treatment of internal
|
||
spaces and [line ending]s. Some, including `Markdown.pl` and
|
||
`showdown`, convert an internal [line ending] into a
|
||
`<br />` tag. But this makes things difficult for those who like to
|
||
hard-wrap their paragraphs, since a line break in the midst of a code
|
||
span will cause an unintended line break in the output. Others just
|
||
leave internal spaces as they are, which is fine if only HTML is being
|
||
targeted.)
|
||
|
||
.
|
||
`foo `` bar`
|
||
.
|
||
<p><code>foo `` bar</code></p>
|
||
.
|
||
|
||
Note that backslash escapes do not work in code spans. All backslashes
|
||
are treated literally:
|
||
|
||
.
|
||
`foo\`bar`
|
||
.
|
||
<p><code>foo\</code>bar`</p>
|
||
.
|
||
|
||
Backslash escapes are never needed, because one can always choose a
|
||
string of *n* backtick characters as delimiters, where the code does
|
||
not contain any strings of exactly *n* backtick characters.
|
||
|
||
Code span backticks have higher precedence than any other inline
|
||
constructs except HTML tags and autolinks. Thus, for example, this is
|
||
not parsed as emphasized text, since the second `*` is part of a code
|
||
span:
|
||
|
||
.
|
||
*foo`*`
|
||
.
|
||
<p>*foo<code>*</code></p>
|
||
.
|
||
|
||
And this is not parsed as a link:
|
||
|
||
.
|
||
[not a `link](/foo`)
|
||
.
|
||
<p>[not a <code>link](/foo</code>)</p>
|
||
.
|
||
|
||
Code spans, HTML tags, and autolinks have the same precedence.
|
||
Thus, this is code:
|
||
|
||
.
|
||
`<a href="`">`
|
||
.
|
||
<p><code><a href="</code>">`</p>
|
||
.
|
||
|
||
But this is an HTML tag:
|
||
|
||
.
|
||
<a href="`">`
|
||
.
|
||
<p><a href="`">`</p>
|
||
.
|
||
|
||
And this is code:
|
||
|
||
.
|
||
`<http://foo.bar.`baz>`
|
||
.
|
||
<p><code><http://foo.bar.</code>baz>`</p>
|
||
.
|
||
|
||
But this is an autolink:
|
||
|
||
.
|
||
<http://foo.bar.`baz>`
|
||
.
|
||
<p><a href="http://foo.bar.%60baz">http://foo.bar.`baz</a>`</p>
|
||
.
|
||
|
||
When a backtick string is not closed by a matching backtick string,
|
||
we just have literal backticks:
|
||
|
||
.
|
||
```foo``
|
||
.
|
||
<p>```foo``</p>
|
||
.
|
||
|
||
.
|
||
`foo
|
||
.
|
||
<p>`foo</p>
|
||
.
|
||
|
||
## Emphasis and strong emphasis
|
||
|
||
John Gruber's original [Markdown syntax
|
||
description](http://daringfireball.net/projects/markdown/syntax#em) says:
|
||
|
||
> Markdown treats asterisks (`*`) and underscores (`_`) as indicators of
|
||
> emphasis. Text wrapped with one `*` or `_` will be wrapped with an HTML
|
||
> `<em>` tag; double `*`'s or `_`'s will be wrapped with an HTML `<strong>`
|
||
> tag.
|
||
|
||
This is enough for most users, but these rules leave much undecided,
|
||
especially when it comes to nested emphasis. The original
|
||
`Markdown.pl` test suite makes it clear that triple `***` and
|
||
`___` delimiters can be used for strong emphasis, and most
|
||
implementations have also allowed the following patterns:
|
||
|
||
``` markdown
|
||
***strong emph***
|
||
***strong** in emph*
|
||
***emph* in strong**
|
||
**in strong *emph***
|
||
*in emph **strong***
|
||
```
|
||
|
||
The following patterns are less widely supported, but the intent
|
||
is clear and they are useful (especially in contexts like bibliography
|
||
entries):
|
||
|
||
``` markdown
|
||
*emph *with emph* in it*
|
||
**strong **with strong** in it**
|
||
```
|
||
|
||
Many implementations have also restricted intraword emphasis to
|
||
the `*` forms, to avoid unwanted emphasis in words containing
|
||
internal underscores. (It is best practice to put these in code
|
||
spans, but users often do not.)
|
||
|
||
``` markdown
|
||
internal emphasis: foo*bar*baz
|
||
no emphasis: foo_bar_baz
|
||
```
|
||
|
||
The rules given below capture all of these patterns, while allowing
|
||
for efficient parsing strategies that do not backtrack.
|
||
|
||
First, some definitions. A [delimiter run](@delimiter-run) is either
|
||
a sequence of one or more `*` characters that is not preceded or
|
||
followed by a `*` character, or a sequence of one or more `_`
|
||
characters that is not preceded or followed by a `_` character.
|
||
|
||
A [left-flanking delimiter run](@left-flanking-delimiter-run) is
|
||
a [delimiter run] that is (a) not followed by [unicode whitespace],
|
||
and (b) either not followed by a [punctuation character], or
|
||
preceded by [unicode whitespace] or a [punctuation character].
|
||
|
||
A [right-flanking delimiter run](@right-flanking-delimiter-run) is
|
||
a [delimiter run] that is (a) not preceded by [unicode whitespace],
|
||
and (b) either not preceded by a [punctuation character], or
|
||
followed by [unicode whitespace] or a [punctuation character].
|
||
|
||
Here are some examples of delimiter runs.
|
||
|
||
- left-flanking but not right-flanking:
|
||
|
||
```
|
||
***abc
|
||
_abc
|
||
**"abc"
|
||
_"abc"
|
||
```
|
||
|
||
- right-flanking but not left-flanking:
|
||
|
||
```
|
||
abc***
|
||
abc_
|
||
"abc"**
|
||
_"abc"
|
||
```
|
||
|
||
- Both right and right-flanking:
|
||
|
||
```
|
||
abc***def
|
||
"abc"_"def"
|
||
```
|
||
|
||
- Neither right nor right-flanking:
|
||
|
||
```
|
||
abc *** def
|
||
a _ b
|
||
```
|
||
|
||
(The idea of distinguishing left-flanking and right-flanking
|
||
delimiter runs based on the character before and the character
|
||
after comes from Roopesh Chander's
|
||
[vfmd](http://www.vfmd.org/vfmd-spec/specification/#procedure-for-identifying-emphasis-tags).
|
||
vfmd uses the terminology "emphasis indicator string" instead of "delimiter
|
||
run," and its rules for distinguishing left- and right-flanking runs
|
||
are a bit more complex than the ones given here.)
|
||
|
||
The following rules define emphasis and strong emphasis:
|
||
|
||
1. A single `*` character [can open emphasis](@can-open-emphasis)
|
||
iff it is part of a [left-flanking delimiter run].
|
||
|
||
2. A single `_` character [can open emphasis] iff
|
||
it is part of a [left-flanking delimiter run]
|
||
and not part of a [right-flanking delimiter run].
|
||
|
||
3. A single `*` character [can close emphasis](@can-close-emphasis)
|
||
iff it is part of a [right-flanking delimiter run].
|
||
|
||
4. A single `_` character [can close emphasis]
|
||
iff it is part of a [right-flanking delimiter run]
|
||
and not part of a [left-flanking delimiter run].
|
||
|
||
5. A double `**` [can open strong emphasis](@can-open-strong-emphasis)
|
||
iff it is part of a [left-flanking delimiter run].
|
||
|
||
6. A double `__` [can open strong emphasis]
|
||
iff it is part of a [left-flanking delimiter run]
|
||
and not part of a [right-flanking delimiter run].
|
||
|
||
7. A double `**` [can close strong emphasis](@can-close-strong-emphasis)
|
||
iff it is part of a [right-flanking delimiter run].
|
||
|
||
8. A double `__` [can close strong emphasis]
|
||
iff it is part of a [right-flanking delimiter run]
|
||
and not part of a [left-flanking delimiter run].
|
||
|
||
9. Emphasis begins with a delimiter that [can open emphasis] and ends
|
||
with a delimiter that [can close emphasis], and that uses the same
|
||
character (`_` or `*`) as the opening delimiter. There must
|
||
be a nonempty sequence of inlines between the open delimiter
|
||
and the closing delimiter; these form the contents of the emphasis
|
||
inline.
|
||
|
||
10. Strong emphasis begins with a delimiter that
|
||
[can open strong emphasis] and ends with a delimiter that
|
||
[can close strong emphasis], and that uses the same character
|
||
(`_` or `*`) as the opening delimiter.
|
||
There must be a nonempty sequence of inlines between the open
|
||
delimiter and the closing delimiter; these form the contents of
|
||
the strong emphasis inline.
|
||
|
||
11. A literal `*` character cannot occur at the beginning or end of
|
||
`*`-delimited emphasis or `**`-delimited strong emphasis, unless it
|
||
is backslash-escaped.
|
||
|
||
12. A literal `_` character cannot occur at the beginning or end of
|
||
`_`-delimited emphasis or `__`-delimited strong emphasis, unless it
|
||
is backslash-escaped.
|
||
|
||
Where rules 1--12 above are compatible with multiple parsings,
|
||
the following principles resolve ambiguity:
|
||
|
||
13. The number of nestings should be minimized. Thus, for example,
|
||
an interpretation `<strong>...</strong>` is always preferred to
|
||
`<em><em>...</em></em>`.
|
||
|
||
14. An interpretation `<strong><em>...</em></strong>` is always
|
||
preferred to `<em><strong>..</strong></em>`.
|
||
|
||
15. When two potential emphasis or strong emphasis spans overlap,
|
||
so that the second begins before the first ends and ends after
|
||
the first ends, the first takes precedence. Thus, for example,
|
||
`*foo _bar* baz_` is parsed as `<em>foo _bar</em> baz_` rather
|
||
than `*foo <em>bar* baz</em>`. For the same reason,
|
||
`**foo*bar**` is parsed as `<em><em>foo</em>bar</em>*`
|
||
rather than `<strong>foo*bar</strong>`.
|
||
|
||
16. When there are two potential emphasis or strong emphasis spans
|
||
with the same closing delimiter, the shorter one (the one that
|
||
opens later) takes precedence. Thus, for example,
|
||
`**foo **bar baz**` is parsed as `**foo <strong>bar baz</strong>`
|
||
rather than `<strong>foo **bar baz</strong>`.
|
||
|
||
17. Inline code spans, links, images, and HTML tags group more tightly
|
||
than emphasis. So, when there is a choice between an interpretation
|
||
that contains one of these elements and one that does not, the
|
||
former always wins. Thus, for example, `*[foo*](bar)` is
|
||
parsed as `*<a href="bar">foo*</a>` rather than as
|
||
`<em>[foo</em>](bar)`.
|
||
|
||
These rules can be illustrated through a series of examples.
|
||
|
||
Rule 1:
|
||
|
||
.
|
||
*foo bar*
|
||
.
|
||
<p><em>foo bar</em></p>
|
||
.
|
||
|
||
This is not emphasis, because the opening `*` is followed by
|
||
whitespace, and hence not part of a [left-flanking delimiter run]:
|
||
|
||
.
|
||
a * foo bar*
|
||
.
|
||
<p>a * foo bar*</p>
|
||
.
|
||
|
||
This is not emphasis, because the opening `*` is preceded
|
||
by an alphanumeric and followed by punctuation, and hence
|
||
not part of a [left-flanking delimiter run]:
|
||
|
||
.
|
||
a*"foo"*
|
||
.
|
||
<p>a*"foo"*</p>
|
||
.
|
||
|
||
Unicode nonbreaking spaces count as whitespace, too:
|
||
|
||
.
|
||
* a *
|
||
.
|
||
<p>* a *</p>
|
||
.
|
||
|
||
Intraword emphasis with `*` is permitted:
|
||
|
||
.
|
||
foo*bar*
|
||
.
|
||
<p>foo<em>bar</em></p>
|
||
.
|
||
|
||
.
|
||
5*6*78
|
||
.
|
||
<p>5<em>6</em>78</p>
|
||
.
|
||
|
||
Rule 2:
|
||
|
||
.
|
||
_foo bar_
|
||
.
|
||
<p><em>foo bar</em></p>
|
||
.
|
||
|
||
This is not emphasis, because the opening `_` is followed by
|
||
whitespace:
|
||
|
||
.
|
||
_ foo bar_
|
||
.
|
||
<p>_ foo bar_</p>
|
||
.
|
||
|
||
This is not emphasis, because the opening `_` is preceded
|
||
by an alphanumeric and followed by punctuation:
|
||
|
||
.
|
||
a_"foo"_
|
||
.
|
||
<p>a_"foo"_</p>
|
||
.
|
||
|
||
Emphasis with `_` is not allowed inside words:
|
||
|
||
.
|
||
foo_bar_
|
||
.
|
||
<p>foo_bar_</p>
|
||
.
|
||
|
||
.
|
||
5_6_78
|
||
.
|
||
<p>5_6_78</p>
|
||
.
|
||
|
||
.
|
||
пристаням_стремятся_
|
||
.
|
||
<p>пристаням_стремятся_</p>
|
||
.
|
||
|
||
Here `_` does not generate emphasis, because the first delimiter run
|
||
is right-flanking and the second left-flanking:
|
||
|
||
.
|
||
aa_"bb"_cc
|
||
.
|
||
<p>aa_"bb"_cc</p>
|
||
.
|
||
|
||
Here there is no emphasis, because the delimiter runs are
|
||
both left- and right-flanking:
|
||
|
||
.
|
||
"aa"_"bb"_"cc"
|
||
.
|
||
<p>"aa"_"bb"_"cc"</p>
|
||
.
|
||
|
||
Rule 3:
|
||
|
||
This is not emphasis, because the closing delimiter does
|
||
not match the opening delimiter:
|
||
|
||
.
|
||
_foo*
|
||
.
|
||
<p>_foo*</p>
|
||
.
|
||
|
||
This is not emphasis, because the closing `*` is preceded by
|
||
whitespace:
|
||
|
||
.
|
||
*foo bar *
|
||
.
|
||
<p>*foo bar *</p>
|
||
.
|
||
|
||
This is not emphasis, because the second `*` is
|
||
preceded by punctuation and followed by an alphanumeric
|
||
(hence it is not part of a [right-flanking delimiter run]:
|
||
|
||
.
|
||
*(*foo)
|
||
.
|
||
<p>*(*foo)</p>
|
||
.
|
||
|
||
The point of this restriction is more easily appreciated
|
||
with this example:
|
||
|
||
.
|
||
*(*foo*)*
|
||
.
|
||
<p><em>(<em>foo</em>)</em></p>
|
||
.
|
||
|
||
Intraword emphasis with `*` is allowed:
|
||
|
||
.
|
||
*foo*bar
|
||
.
|
||
<p><em>foo</em>bar</p>
|
||
.
|
||
|
||
|
||
Rule 4:
|
||
|
||
This is not emphasis, because the closing `_` is preceded by
|
||
whitespace:
|
||
|
||
.
|
||
_foo bar _
|
||
.
|
||
<p>_foo bar _</p>
|
||
.
|
||
|
||
This is not emphasis, because the second `_` is
|
||
preceded by punctuation and followed by an alphanumeric:
|
||
|
||
.
|
||
_(_foo)
|
||
.
|
||
<p>_(_foo)</p>
|
||
.
|
||
|
||
This is emphasis within emphasis:
|
||
|
||
.
|
||
_(_foo_)_
|
||
.
|
||
<p><em>(<em>foo</em>)</em></p>
|
||
.
|
||
|
||
Intraword emphasis is disallowed for `_`:
|
||
|
||
.
|
||
_foo_bar
|
||
.
|
||
<p>_foo_bar</p>
|
||
.
|
||
|
||
.
|
||
_пристаням_стремятся
|
||
.
|
||
<p>_пристаням_стремятся</p>
|
||
.
|
||
|
||
.
|
||
_foo_bar_baz_
|
||
.
|
||
<p><em>foo_bar_baz</em></p>
|
||
.
|
||
|
||
Rule 5:
|
||
|
||
.
|
||
**foo bar**
|
||
.
|
||
<p><strong>foo bar</strong></p>
|
||
.
|
||
|
||
This is not strong emphasis, because the opening delimiter is
|
||
followed by whitespace:
|
||
|
||
.
|
||
** foo bar**
|
||
.
|
||
<p>** foo bar**</p>
|
||
.
|
||
|
||
This is not strong emphasis, because the opening `**` is preceded
|
||
by an alphanumeric and followed by punctuation, and hence
|
||
not part of a [left-flanking delimiter run]:
|
||
|
||
.
|
||
a**"foo"**
|
||
.
|
||
<p>a**"foo"**</p>
|
||
.
|
||
|
||
Intraword strong emphasis with `**` is permitted:
|
||
|
||
.
|
||
foo**bar**
|
||
.
|
||
<p>foo<strong>bar</strong></p>
|
||
.
|
||
|
||
Rule 6:
|
||
|
||
.
|
||
__foo bar__
|
||
.
|
||
<p><strong>foo bar</strong></p>
|
||
.
|
||
|
||
This is not strong emphasis, because the opening delimiter is
|
||
followed by whitespace:
|
||
|
||
.
|
||
__ foo bar__
|
||
.
|
||
<p>__ foo bar__</p>
|
||
.
|
||
|
||
This is not strong emphasis, because the opening `__` is preceded
|
||
by an alphanumeric and followed by punctuation:
|
||
|
||
.
|
||
a__"foo"__
|
||
.
|
||
<p>a__"foo"__</p>
|
||
.
|
||
|
||
Intraword strong emphasis is forbidden with `__`:
|
||
|
||
.
|
||
foo__bar__
|
||
.
|
||
<p>foo__bar__</p>
|
||
.
|
||
|
||
.
|
||
5__6__78
|
||
.
|
||
<p>5__6__78</p>
|
||
.
|
||
|
||
.
|
||
пристаням__стремятся__
|
||
.
|
||
<p>пристаням__стремятся__</p>
|
||
.
|
||
|
||
.
|
||
__foo, __bar__, baz__
|
||
.
|
||
<p><strong>foo, <strong>bar</strong>, baz</strong></p>
|
||
.
|
||
|
||
Rule 7:
|
||
|
||
This is not strong emphasis, because the closing delimiter is preceded
|
||
by whitespace:
|
||
|
||
.
|
||
**foo bar **
|
||
.
|
||
<p>**foo bar **</p>
|
||
.
|
||
|
||
(Nor can it be interpreted as an emphasized `*foo bar *`, because of
|
||
Rule 11.)
|
||
|
||
This is not strong emphasis, because the second `**` is
|
||
preceded by punctuation and followed by an alphanumeric:
|
||
|
||
.
|
||
**(**foo)
|
||
.
|
||
<p>**(**foo)</p>
|
||
.
|
||
|
||
The point of this restriction is more easily appreciated
|
||
with these examples:
|
||
|
||
.
|
||
*(**foo**)*
|
||
.
|
||
<p><em>(<strong>foo</strong>)</em></p>
|
||
.
|
||
|
||
.
|
||
**Gomphocarpus (*Gomphocarpus physocarpus*, syn.
|
||
*Asclepias physocarpa*)**
|
||
.
|
||
<p><strong>Gomphocarpus (<em>Gomphocarpus physocarpus</em>, syn.
|
||
<em>Asclepias physocarpa</em>)</strong></p>
|
||
.
|
||
|
||
.
|
||
**foo "*bar*" foo**
|
||
.
|
||
<p><strong>foo "<em>bar</em>" foo</strong></p>
|
||
.
|
||
|
||
Intraword emphasis:
|
||
|
||
.
|
||
**foo**bar
|
||
.
|
||
<p><strong>foo</strong>bar</p>
|
||
.
|
||
|
||
Rule 8:
|
||
|
||
This is not strong emphasis, because the closing delimiter is
|
||
preceded by whitespace:
|
||
|
||
.
|
||
__foo bar __
|
||
.
|
||
<p>__foo bar __</p>
|
||
.
|
||
|
||
This is not strong emphasis, because the second `__` is
|
||
preceded by punctuation and followed by an alphanumeric:
|
||
|
||
.
|
||
__(__foo)
|
||
.
|
||
<p>__(__foo)</p>
|
||
.
|
||
|
||
The point of this restriction is more easily appreciated
|
||
with this example:
|
||
|
||
.
|
||
_(__foo__)_
|
||
.
|
||
<p><em>(<strong>foo</strong>)</em></p>
|
||
.
|
||
|
||
Intraword strong emphasis is forbidden with `__`:
|
||
|
||
.
|
||
__foo__bar
|
||
.
|
||
<p>__foo__bar</p>
|
||
.
|
||
|
||
.
|
||
__пристаням__стремятся
|
||
.
|
||
<p>__пристаням__стремятся</p>
|
||
.
|
||
|
||
.
|
||
__foo__bar__baz__
|
||
.
|
||
<p><strong>foo__bar__baz</strong></p>
|
||
.
|
||
|
||
Rule 9:
|
||
|
||
Any nonempty sequence of inline elements can be the contents of an
|
||
emphasized span.
|
||
|
||
.
|
||
*foo [bar](/url)*
|
||
.
|
||
<p><em>foo <a href="/url">bar</a></em></p>
|
||
.
|
||
|
||
.
|
||
*foo
|
||
bar*
|
||
.
|
||
<p><em>foo
|
||
bar</em></p>
|
||
.
|
||
|
||
In particular, emphasis and strong emphasis can be nested
|
||
inside emphasis:
|
||
|
||
.
|
||
_foo __bar__ baz_
|
||
.
|
||
<p><em>foo <strong>bar</strong> baz</em></p>
|
||
.
|
||
|
||
.
|
||
_foo _bar_ baz_
|
||
.
|
||
<p><em>foo <em>bar</em> baz</em></p>
|
||
.
|
||
|
||
.
|
||
__foo_ bar_
|
||
.
|
||
<p><em><em>foo</em> bar</em></p>
|
||
.
|
||
|
||
.
|
||
*foo *bar**
|
||
.
|
||
<p><em>foo <em>bar</em></em></p>
|
||
.
|
||
|
||
.
|
||
*foo **bar** baz*
|
||
.
|
||
<p><em>foo <strong>bar</strong> baz</em></p>
|
||
.
|
||
|
||
But note:
|
||
|
||
.
|
||
*foo**bar**baz*
|
||
.
|
||
<p><em>foo</em><em>bar</em><em>baz</em></p>
|
||
.
|
||
|
||
The difference is that in the preceding case, the internal delimiters
|
||
[can close emphasis], while in the cases with spaces, they cannot.
|
||
|
||
.
|
||
***foo** bar*
|
||
.
|
||
<p><em><strong>foo</strong> bar</em></p>
|
||
.
|
||
|
||
.
|
||
*foo **bar***
|
||
.
|
||
<p><em>foo <strong>bar</strong></em></p>
|
||
.
|
||
|
||
Note, however, that in the following case we get no strong
|
||
emphasis, because the opening delimiter is closed by the first
|
||
`*` before `bar`:
|
||
|
||
.
|
||
*foo**bar***
|
||
.
|
||
<p><em>foo</em><em>bar</em>**</p>
|
||
.
|
||
|
||
|
||
Indefinite levels of nesting are possible:
|
||
|
||
.
|
||
*foo **bar *baz* bim** bop*
|
||
.
|
||
<p><em>foo <strong>bar <em>baz</em> bim</strong> bop</em></p>
|
||
.
|
||
|
||
.
|
||
*foo [*bar*](/url)*
|
||
.
|
||
<p><em>foo <a href="/url"><em>bar</em></a></em></p>
|
||
.
|
||
|
||
There can be no empty emphasis or strong emphasis:
|
||
|
||
.
|
||
** is not an empty emphasis
|
||
.
|
||
<p>** is not an empty emphasis</p>
|
||
.
|
||
|
||
.
|
||
**** is not an empty strong emphasis
|
||
.
|
||
<p>**** is not an empty strong emphasis</p>
|
||
.
|
||
|
||
|
||
Rule 10:
|
||
|
||
Any nonempty sequence of inline elements can be the contents of an
|
||
strongly emphasized span.
|
||
|
||
.
|
||
**foo [bar](/url)**
|
||
.
|
||
<p><strong>foo <a href="/url">bar</a></strong></p>
|
||
.
|
||
|
||
.
|
||
**foo
|
||
bar**
|
||
.
|
||
<p><strong>foo
|
||
bar</strong></p>
|
||
.
|
||
|
||
In particular, emphasis and strong emphasis can be nested
|
||
inside strong emphasis:
|
||
|
||
.
|
||
__foo _bar_ baz__
|
||
.
|
||
<p><strong>foo <em>bar</em> baz</strong></p>
|
||
.
|
||
|
||
.
|
||
__foo __bar__ baz__
|
||
.
|
||
<p><strong>foo <strong>bar</strong> baz</strong></p>
|
||
.
|
||
|
||
.
|
||
____foo__ bar__
|
||
.
|
||
<p><strong><strong>foo</strong> bar</strong></p>
|
||
.
|
||
|
||
.
|
||
**foo **bar****
|
||
.
|
||
<p><strong>foo <strong>bar</strong></strong></p>
|
||
.
|
||
|
||
.
|
||
**foo *bar* baz**
|
||
.
|
||
<p><strong>foo <em>bar</em> baz</strong></p>
|
||
.
|
||
|
||
But note:
|
||
|
||
.
|
||
**foo*bar*baz**
|
||
.
|
||
<p><em><em>foo</em>bar</em>baz**</p>
|
||
.
|
||
|
||
The difference is that in the preceding case, the internal delimiters
|
||
[can close emphasis], while in the cases with spaces, they cannot.
|
||
|
||
.
|
||
***foo* bar**
|
||
.
|
||
<p><strong><em>foo</em> bar</strong></p>
|
||
.
|
||
|
||
.
|
||
**foo *bar***
|
||
.
|
||
<p><strong>foo <em>bar</em></strong></p>
|
||
.
|
||
|
||
Indefinite levels of nesting are possible:
|
||
|
||
.
|
||
**foo *bar **baz**
|
||
bim* bop**
|
||
.
|
||
<p><strong>foo <em>bar <strong>baz</strong>
|
||
bim</em> bop</strong></p>
|
||
.
|
||
|
||
.
|
||
**foo [*bar*](/url)**
|
||
.
|
||
<p><strong>foo <a href="/url"><em>bar</em></a></strong></p>
|
||
.
|
||
|
||
There can be no empty emphasis or strong emphasis:
|
||
|
||
.
|
||
__ is not an empty emphasis
|
||
.
|
||
<p>__ is not an empty emphasis</p>
|
||
.
|
||
|
||
.
|
||
____ is not an empty strong emphasis
|
||
.
|
||
<p>____ is not an empty strong emphasis</p>
|
||
.
|
||
|
||
|
||
Rule 11:
|
||
|
||
.
|
||
foo ***
|
||
.
|
||
<p>foo ***</p>
|
||
.
|
||
|
||
.
|
||
foo *\**
|
||
.
|
||
<p>foo <em>*</em></p>
|
||
.
|
||
|
||
.
|
||
foo *_*
|
||
.
|
||
<p>foo <em>_</em></p>
|
||
.
|
||
|
||
.
|
||
foo *****
|
||
.
|
||
<p>foo *****</p>
|
||
.
|
||
|
||
.
|
||
foo **\***
|
||
.
|
||
<p>foo <strong>*</strong></p>
|
||
.
|
||
|
||
.
|
||
foo **_**
|
||
.
|
||
<p>foo <strong>_</strong></p>
|
||
.
|
||
|
||
Note that when delimiters do not match evenly, Rule 11 determines
|
||
that the excess literal `*` characters will appear outside of the
|
||
emphasis, rather than inside it:
|
||
|
||
.
|
||
**foo*
|
||
.
|
||
<p>*<em>foo</em></p>
|
||
.
|
||
|
||
.
|
||
*foo**
|
||
.
|
||
<p><em>foo</em>*</p>
|
||
.
|
||
|
||
.
|
||
***foo**
|
||
.
|
||
<p>*<strong>foo</strong></p>
|
||
.
|
||
|
||
.
|
||
****foo*
|
||
.
|
||
<p>***<em>foo</em></p>
|
||
.
|
||
|
||
.
|
||
**foo***
|
||
.
|
||
<p><strong>foo</strong>*</p>
|
||
.
|
||
|
||
.
|
||
*foo****
|
||
.
|
||
<p><em>foo</em>***</p>
|
||
.
|
||
|
||
|
||
Rule 12:
|
||
|
||
.
|
||
foo ___
|
||
.
|
||
<p>foo ___</p>
|
||
.
|
||
|
||
.
|
||
foo _\__
|
||
.
|
||
<p>foo <em>_</em></p>
|
||
.
|
||
|
||
.
|
||
foo _*_
|
||
.
|
||
<p>foo <em>*</em></p>
|
||
.
|
||
|
||
.
|
||
foo _____
|
||
.
|
||
<p>foo _____</p>
|
||
.
|
||
|
||
.
|
||
foo __\___
|
||
.
|
||
<p>foo <strong>_</strong></p>
|
||
.
|
||
|
||
.
|
||
foo __*__
|
||
.
|
||
<p>foo <strong>*</strong></p>
|
||
.
|
||
|
||
.
|
||
__foo_
|
||
.
|
||
<p>_<em>foo</em></p>
|
||
.
|
||
|
||
Note that when delimiters do not match evenly, Rule 12 determines
|
||
that the excess literal `_` characters will appear outside of the
|
||
emphasis, rather than inside it:
|
||
|
||
.
|
||
_foo__
|
||
.
|
||
<p><em>foo</em>_</p>
|
||
.
|
||
|
||
.
|
||
___foo__
|
||
.
|
||
<p>_<strong>foo</strong></p>
|
||
.
|
||
|
||
.
|
||
____foo_
|
||
.
|
||
<p>___<em>foo</em></p>
|
||
.
|
||
|
||
.
|
||
__foo___
|
||
.
|
||
<p><strong>foo</strong>_</p>
|
||
.
|
||
|
||
.
|
||
_foo____
|
||
.
|
||
<p><em>foo</em>___</p>
|
||
.
|
||
|
||
Rule 13 implies that if you want emphasis nested directly inside
|
||
emphasis, you must use different delimiters:
|
||
|
||
.
|
||
**foo**
|
||
.
|
||
<p><strong>foo</strong></p>
|
||
.
|
||
|
||
.
|
||
*_foo_*
|
||
.
|
||
<p><em><em>foo</em></em></p>
|
||
.
|
||
|
||
.
|
||
__foo__
|
||
.
|
||
<p><strong>foo</strong></p>
|
||
.
|
||
|
||
.
|
||
_*foo*_
|
||
.
|
||
<p><em><em>foo</em></em></p>
|
||
.
|
||
|
||
However, strong emphasis within strong emphasis is possible without
|
||
switching delimiters:
|
||
|
||
.
|
||
****foo****
|
||
.
|
||
<p><strong><strong>foo</strong></strong></p>
|
||
.
|
||
|
||
.
|
||
____foo____
|
||
.
|
||
<p><strong><strong>foo</strong></strong></p>
|
||
.
|
||
|
||
|
||
Rule 13 can be applied to arbitrarily long sequences of
|
||
delimiters:
|
||
|
||
.
|
||
******foo******
|
||
.
|
||
<p><strong><strong><strong>foo</strong></strong></strong></p>
|
||
.
|
||
|
||
Rule 14:
|
||
|
||
.
|
||
***foo***
|
||
.
|
||
<p><strong><em>foo</em></strong></p>
|
||
.
|
||
|
||
.
|
||
_____foo_____
|
||
.
|
||
<p><strong><strong><em>foo</em></strong></strong></p>
|
||
.
|
||
|
||
Rule 15:
|
||
|
||
.
|
||
*foo _bar* baz_
|
||
.
|
||
<p><em>foo _bar</em> baz_</p>
|
||
.
|
||
|
||
.
|
||
**foo*bar**
|
||
.
|
||
<p><em><em>foo</em>bar</em>*</p>
|
||
.
|
||
|
||
|
||
Rule 16:
|
||
|
||
.
|
||
**foo **bar baz**
|
||
.
|
||
<p>**foo <strong>bar baz</strong></p>
|
||
.
|
||
|
||
.
|
||
*foo *bar baz*
|
||
.
|
||
<p>*foo <em>bar baz</em></p>
|
||
.
|
||
|
||
Rule 17:
|
||
|
||
.
|
||
*[bar*](/url)
|
||
.
|
||
<p>*<a href="/url">bar*</a></p>
|
||
.
|
||
|
||
.
|
||
_foo [bar_](/url)
|
||
.
|
||
<p>_foo <a href="/url">bar_</a></p>
|
||
.
|
||
|
||
.
|
||
*<img src="foo" title="*"/>
|
||
.
|
||
<p>*<img src="foo" title="*"/></p>
|
||
.
|
||
|
||
.
|
||
**<a href="**">
|
||
.
|
||
<p>**<a href="**"></p>
|
||
.
|
||
|
||
.
|
||
__<a href="__">
|
||
.
|
||
<p>__<a href="__"></p>
|
||
.
|
||
|
||
.
|
||
*a `*`*
|
||
.
|
||
<p><em>a <code>*</code></em></p>
|
||
.
|
||
|
||
.
|
||
_a `_`_
|
||
.
|
||
<p><em>a <code>_</code></em></p>
|
||
.
|
||
|
||
.
|
||
**a<http://foo.bar?q=**>
|
||
.
|
||
<p>**a<a href="http://foo.bar?q=**">http://foo.bar?q=**</a></p>
|
||
.
|
||
|
||
.
|
||
__a<http://foo.bar?q=__>
|
||
.
|
||
<p>__a<a href="http://foo.bar?q=__">http://foo.bar?q=__</a></p>
|
||
.
|
||
|
||
|
||
## Links
|
||
|
||
A link contains [link text] (the visible text), a [link destination]
|
||
(the URI that is the link destination), and optionally a [link title].
|
||
There are two basic kinds of links in Markdown. In [inline link]s the
|
||
destination and title are given immediately after the link text. In
|
||
[reference link]s the destination and title are defined elsewhere in
|
||
the document.
|
||
|
||
A [link text](@link-text) consists of a sequence of zero or more
|
||
inline elements enclosed by square brackets (`[` and `]`). The
|
||
following rules apply:
|
||
|
||
- Links may not contain other links, at any level of nesting.
|
||
|
||
- Brackets are allowed in the [link text] only if (a) they
|
||
are backslash-escaped or (b) they appear as a matched pair of brackets,
|
||
with an open bracket `[`, a sequence of zero or more inlines, and
|
||
a close bracket `]`.
|
||
|
||
- Backtick [code span]s, [autolink]s, and raw [HTML tag]s bind more tightly
|
||
than the brackets in link text. Thus, for example,
|
||
`` [foo`]` `` could not be a link text, since the second `]`
|
||
is part of a code span.
|
||
|
||
- The brackets in link text bind more tightly than markers for
|
||
[emphasis and strong emphasis]. Thus, for example, `*[foo*](url)` is a link.
|
||
|
||
A [link destination](@link-destination) consists of either
|
||
|
||
- a sequence of zero or more characters between an opening `<` and a
|
||
closing `>` that contains no line breaks or unescaped `<` or `>`
|
||
characters, or
|
||
|
||
- a nonempty sequence of characters that does not include
|
||
ASCII space or control characters, and includes parentheses
|
||
only if (a) they are backslash-escaped or (b) they are part of
|
||
a balanced pair of unescaped parentheses that is not itself
|
||
inside a balanced pair of unescaped paretheses.
|
||
|
||
A [link title](@link-title) consists of either
|
||
|
||
- a sequence of zero or more characters between straight double-quote
|
||
characters (`"`), including a `"` character only if it is
|
||
backslash-escaped, or
|
||
|
||
- a sequence of zero or more characters between straight single-quote
|
||
characters (`'`), including a `'` character only if it is
|
||
backslash-escaped, or
|
||
|
||
- a sequence of zero or more characters between matching parentheses
|
||
(`(...)`), including a `)` character only if it is backslash-escaped.
|
||
|
||
An [inline link](@inline-link) consists of a [link text] followed immediately
|
||
by a left parenthesis `(`, optional [whitespace], an optional
|
||
[link destination], an optional [link title] separated from the link
|
||
destination by [whitespace], optional [whitespace], and a right
|
||
parenthesis `)`. The link's text consists of the inlines contained
|
||
in the [link text] (excluding the enclosing square brackets).
|
||
The link's URI consists of the link destination, excluding enclosing
|
||
`<...>` if present, with backslash-escapes in effect as described
|
||
above. The link's title consists of the link title, excluding its
|
||
enclosing delimiters, with backslash-escapes in effect as described
|
||
above.
|
||
|
||
Here is a simple inline link:
|
||
|
||
.
|
||
[link](/uri "title")
|
||
.
|
||
<p><a href="/uri" title="title">link</a></p>
|
||
.
|
||
|
||
The title may be omitted:
|
||
|
||
.
|
||
[link](/uri)
|
||
.
|
||
<p><a href="/uri">link</a></p>
|
||
.
|
||
|
||
Both the title and the destination may be omitted:
|
||
|
||
.
|
||
[link]()
|
||
.
|
||
<p><a href="">link</a></p>
|
||
.
|
||
|
||
.
|
||
[link](<>)
|
||
.
|
||
<p><a href="">link</a></p>
|
||
.
|
||
|
||
If the destination contains spaces, it must be enclosed in pointy
|
||
braces:
|
||
|
||
.
|
||
[link](/my uri)
|
||
.
|
||
<p>[link](/my uri)</p>
|
||
.
|
||
|
||
.
|
||
[link](</my uri>)
|
||
.
|
||
<p><a href="/my%20uri">link</a></p>
|
||
.
|
||
|
||
The destination cannot contain line breaks, even with pointy braces:
|
||
|
||
.
|
||
[link](foo
|
||
bar)
|
||
.
|
||
<p>[link](foo
|
||
bar)</p>
|
||
.
|
||
|
||
.
|
||
[link](<foo
|
||
bar>)
|
||
.
|
||
<p>[link](<foo
|
||
bar>)</p>
|
||
.
|
||
|
||
One level of balanced parentheses is allowed without escaping:
|
||
|
||
.
|
||
[link]((foo)and(bar))
|
||
.
|
||
<p><a href="(foo)and(bar)">link</a></p>
|
||
.
|
||
|
||
However, if you have parentheses within parentheses, you need to escape
|
||
or use the `<...>` form:
|
||
|
||
.
|
||
[link](foo(and(bar)))
|
||
.
|
||
<p>[link](foo(and(bar)))</p>
|
||
.
|
||
|
||
.
|
||
[link](foo(and\(bar\)))
|
||
.
|
||
<p><a href="foo(and(bar))">link</a></p>
|
||
.
|
||
|
||
.
|
||
[link](<foo(and(bar))>)
|
||
.
|
||
<p><a href="foo(and(bar))">link</a></p>
|
||
.
|
||
|
||
Parentheses and other symbols can also be escaped, as usual
|
||
in Markdown:
|
||
|
||
.
|
||
[link](foo\)\:)
|
||
.
|
||
<p><a href="foo):">link</a></p>
|
||
.
|
||
|
||
URL-escaping should be left alone inside the destination, as all
|
||
URL-escaped characters are also valid URL characters. HTML entities in
|
||
the destination will be parsed into their UTF-8 codepoints, as usual, and
|
||
optionally URL-escaped when written as HTML.
|
||
|
||
.
|
||
[link](foo%20bä)
|
||
.
|
||
<p><a href="foo%20b%C3%A4">link</a></p>
|
||
.
|
||
|
||
Note that, because titles can often be parsed as destinations,
|
||
if you try to omit the destination and keep the title, you'll
|
||
get unexpected results:
|
||
|
||
.
|
||
[link]("title")
|
||
.
|
||
<p><a href="%22title%22">link</a></p>
|
||
.
|
||
|
||
Titles may be in single quotes, double quotes, or parentheses:
|
||
|
||
.
|
||
[link](/url "title")
|
||
[link](/url 'title')
|
||
[link](/url (title))
|
||
.
|
||
<p><a href="/url" title="title">link</a>
|
||
<a href="/url" title="title">link</a>
|
||
<a href="/url" title="title">link</a></p>
|
||
.
|
||
|
||
Backslash escapes and entities may be used in titles:
|
||
|
||
.
|
||
[link](/url "title \""")
|
||
.
|
||
<p><a href="/url" title="title """>link</a></p>
|
||
.
|
||
|
||
Nested balanced quotes are not allowed without escaping:
|
||
|
||
.
|
||
[link](/url "title "and" title")
|
||
.
|
||
<p>[link](/url "title "and" title")</p>
|
||
.
|
||
|
||
But it is easy to work around this by using a different quote type:
|
||
|
||
.
|
||
[link](/url 'title "and" title')
|
||
.
|
||
<p><a href="/url" title="title "and" title">link</a></p>
|
||
.
|
||
|
||
(Note: `Markdown.pl` did allow double quotes inside a double-quoted
|
||
title, and its test suite included a test demonstrating this.
|
||
But it is hard to see a good rationale for the extra complexity this
|
||
brings, since there are already many ways---backslash escaping,
|
||
entities, or using a different quote type for the enclosing title---to
|
||
write titles containing double quotes. `Markdown.pl`'s handling of
|
||
titles has a number of other strange features. For example, it allows
|
||
single-quoted titles in inline links, but not reference links. And, in
|
||
reference links but not inline links, it allows a title to begin with
|
||
`"` and end with `)`. `Markdown.pl` 1.0.1 even allows titles with no closing
|
||
quotation mark, though 1.0.2b8 does not. It seems preferable to adopt
|
||
a simple, rational rule that works the same way in inline links and
|
||
link reference definitions.)
|
||
|
||
[Whitespace] is allowed around the destination and title:
|
||
|
||
.
|
||
[link]( /uri
|
||
"title" )
|
||
.
|
||
<p><a href="/uri" title="title">link</a></p>
|
||
.
|
||
|
||
But it is not allowed between the link text and the
|
||
following parenthesis:
|
||
|
||
.
|
||
[link] (/uri)
|
||
.
|
||
<p>[link] (/uri)</p>
|
||
.
|
||
|
||
The link text may contain balanced brackets, but not unbalanced ones,
|
||
unless they are escaped:
|
||
|
||
.
|
||
[link [foo [bar]]](/uri)
|
||
.
|
||
<p><a href="/uri">link [foo [bar]]</a></p>
|
||
.
|
||
|
||
.
|
||
[link] bar](/uri)
|
||
.
|
||
<p>[link] bar](/uri)</p>
|
||
.
|
||
|
||
.
|
||
[link [bar](/uri)
|
||
.
|
||
<p>[link <a href="/uri">bar</a></p>
|
||
.
|
||
|
||
.
|
||
[link \[bar](/uri)
|
||
.
|
||
<p><a href="/uri">link [bar</a></p>
|
||
.
|
||
|
||
The link text may contain inline content:
|
||
|
||
.
|
||
[link *foo **bar** `#`*](/uri)
|
||
.
|
||
<p><a href="/uri">link <em>foo <strong>bar</strong> <code>#</code></em></a></p>
|
||
.
|
||
|
||
.
|
||
[](/uri)
|
||
.
|
||
<p><a href="/uri"><img src="moon.jpg" alt="moon" /></a></p>
|
||
.
|
||
|
||
However, links may not contain other links, at any level of nesting.
|
||
|
||
.
|
||
[foo [bar](/uri)](/uri)
|
||
.
|
||
<p>[foo <a href="/uri">bar</a>](/uri)</p>
|
||
.
|
||
|
||
.
|
||
[foo *[bar [baz](/uri)](/uri)*](/uri)
|
||
.
|
||
<p>[foo <em>[bar <a href="/uri">baz</a>](/uri)</em>](/uri)</p>
|
||
.
|
||
|
||
.
|
||
](uri2)](uri3)
|
||
.
|
||
<p><img src="uri3" alt="[foo](uri2)" /></p>
|
||
.
|
||
|
||
These cases illustrate the precedence of link text grouping over
|
||
emphasis grouping:
|
||
|
||
.
|
||
*[foo*](/uri)
|
||
.
|
||
<p>*<a href="/uri">foo*</a></p>
|
||
.
|
||
|
||
.
|
||
[foo *bar](baz*)
|
||
.
|
||
<p><a href="baz*">foo *bar</a></p>
|
||
.
|
||
|
||
Note that brackets that *aren't* part of links do not take
|
||
precedence:
|
||
|
||
.
|
||
*foo [bar* baz]
|
||
.
|
||
<p><em>foo [bar</em> baz]</p>
|
||
.
|
||
|
||
These cases illustrate the precedence of HTML tags, code spans,
|
||
and autolinks over link grouping:
|
||
|
||
.
|
||
[foo <bar attr="](baz)">
|
||
.
|
||
<p>[foo <bar attr="](baz)"></p>
|
||
.
|
||
|
||
.
|
||
[foo`](/uri)`
|
||
.
|
||
<p>[foo<code>](/uri)</code></p>
|
||
.
|
||
|
||
.
|
||
[foo<http://example.com?search=](uri)>
|
||
.
|
||
<p>[foo<a href="http://example.com?search=%5D(uri)">http://example.com?search=](uri)</a></p>
|
||
.
|
||
|
||
There are three kinds of [reference link](@reference-link)s:
|
||
[full](#full-reference-link), [collapsed](#collapsed-reference-link),
|
||
and [shortcut](#shortcut-reference-link).
|
||
|
||
A [full reference link](@full-reference-link)
|
||
consists of a [link text], optional [whitespace], and a [link label]
|
||
that [matches] a [link reference definition] elsewhere in the document.
|
||
|
||
A [link label](@link-label) begins with a left bracket (`[`) and ends
|
||
with the first right bracket (`]`) that is not backslash-escaped.
|
||
Unescaped square bracket characters are not allowed in
|
||
[link label]s. A link label can have at most 999
|
||
characters inside the square brackets.
|
||
|
||
One label [matches](@matches)
|
||
another just in case their normalized forms are equal. To normalize a
|
||
label, perform the *unicode case fold* and collapse consecutive internal
|
||
[whitespace] to a single space. If there are multiple
|
||
matching reference link definitions, the one that comes first in the
|
||
document is used. (It is desirable in such cases to emit a warning.)
|
||
|
||
The contents of the first link label are parsed as inlines, which are
|
||
used as the link's text. The link's URI and title are provided by the
|
||
matching [link reference definition].
|
||
|
||
Here is a simple example:
|
||
|
||
.
|
||
[foo][bar]
|
||
|
||
[bar]: /url "title"
|
||
.
|
||
<p><a href="/url" title="title">foo</a></p>
|
||
.
|
||
|
||
The rules for the [link text] are the same as with
|
||
[inline link]s. Thus:
|
||
|
||
The link text may contain balanced brackets, but not unbalanced ones,
|
||
unless they are escaped:
|
||
|
||
.
|
||
[link [foo [bar]]][ref]
|
||
|
||
[ref]: /uri
|
||
.
|
||
<p><a href="/uri">link [foo [bar]]</a></p>
|
||
.
|
||
|
||
.
|
||
[link \[bar][ref]
|
||
|
||
[ref]: /uri
|
||
.
|
||
<p><a href="/uri">link [bar</a></p>
|
||
.
|
||
|
||
The link text may contain inline content:
|
||
|
||
.
|
||
[link *foo **bar** `#`*][ref]
|
||
|
||
[ref]: /uri
|
||
.
|
||
<p><a href="/uri">link <em>foo <strong>bar</strong> <code>#</code></em></a></p>
|
||
.
|
||
|
||
.
|
||
[][ref]
|
||
|
||
[ref]: /uri
|
||
.
|
||
<p><a href="/uri"><img src="moon.jpg" alt="moon" /></a></p>
|
||
.
|
||
|
||
However, links may not contain other links, at any level of nesting.
|
||
|
||
.
|
||
[foo [bar](/uri)][ref]
|
||
|
||
[ref]: /uri
|
||
.
|
||
<p>[foo <a href="/uri">bar</a>]<a href="/uri">ref</a></p>
|
||
.
|
||
|
||
.
|
||
[foo *bar [baz][ref]*][ref]
|
||
|
||
[ref]: /uri
|
||
.
|
||
<p>[foo <em>bar <a href="/uri">baz</a></em>]<a href="/uri">ref</a></p>
|
||
.
|
||
|
||
(In the examples above, we have two [shortcut reference link]s
|
||
instead of one [full reference link].)
|
||
|
||
The following cases illustrate the precedence of link text grouping over
|
||
emphasis grouping:
|
||
|
||
.
|
||
*[foo*][ref]
|
||
|
||
[ref]: /uri
|
||
.
|
||
<p>*<a href="/uri">foo*</a></p>
|
||
.
|
||
|
||
.
|
||
[foo *bar][ref]
|
||
|
||
[ref]: /uri
|
||
.
|
||
<p><a href="/uri">foo *bar</a></p>
|
||
.
|
||
|
||
These cases illustrate the precedence of HTML tags, code spans,
|
||
and autolinks over link grouping:
|
||
|
||
.
|
||
[foo <bar attr="][ref]">
|
||
|
||
[ref]: /uri
|
||
.
|
||
<p>[foo <bar attr="][ref]"></p>
|
||
.
|
||
|
||
.
|
||
[foo`][ref]`
|
||
|
||
[ref]: /uri
|
||
.
|
||
<p>[foo<code>][ref]</code></p>
|
||
.
|
||
|
||
.
|
||
[foo<http://example.com?search=][ref]>
|
||
|
||
[ref]: /uri
|
||
.
|
||
<p>[foo<a href="http://example.com?search=%5D%5Bref%5D">http://example.com?search=][ref]</a></p>
|
||
.
|
||
|
||
Matching is case-insensitive:
|
||
|
||
.
|
||
[foo][BaR]
|
||
|
||
[bar]: /url "title"
|
||
.
|
||
<p><a href="/url" title="title">foo</a></p>
|
||
.
|
||
|
||
Unicode case fold is used:
|
||
|
||
.
|
||
[Толпой][Толпой] is a Russian word.
|
||
|
||
[ТОЛПОЙ]: /url
|
||
.
|
||
<p><a href="/url">Толпой</a> is a Russian word.</p>
|
||
.
|
||
|
||
Consecutive internal [whitespace] is treated as one space for
|
||
purposes of determining matching:
|
||
|
||
.
|
||
[Foo
|
||
bar]: /url
|
||
|
||
[Baz][Foo bar]
|
||
.
|
||
<p><a href="/url">Baz</a></p>
|
||
.
|
||
|
||
There can be [whitespace] between the [link text] and the [link label]:
|
||
|
||
.
|
||
[foo] [bar]
|
||
|
||
[bar]: /url "title"
|
||
.
|
||
<p><a href="/url" title="title">foo</a></p>
|
||
.
|
||
|
||
.
|
||
[foo]
|
||
[bar]
|
||
|
||
[bar]: /url "title"
|
||
.
|
||
<p><a href="/url" title="title">foo</a></p>
|
||
.
|
||
|
||
When there are multiple matching [link reference definition]s,
|
||
the first is used:
|
||
|
||
.
|
||
[foo]: /url1
|
||
|
||
[foo]: /url2
|
||
|
||
[bar][foo]
|
||
.
|
||
<p><a href="/url1">bar</a></p>
|
||
.
|
||
|
||
Note that matching is performed on normalized strings, not parsed
|
||
inline content. So the following does not match, even though the
|
||
labels define equivalent inline content:
|
||
|
||
.
|
||
[bar][foo\!]
|
||
|
||
[foo!]: /url
|
||
.
|
||
<p>[bar][foo!]</p>
|
||
.
|
||
|
||
[Link label]s cannot contain brackets, unless they are
|
||
backslash-escaped:
|
||
|
||
.
|
||
[foo][ref[]
|
||
|
||
[ref[]: /uri
|
||
.
|
||
<p>[foo][ref[]</p>
|
||
<p>[ref[]: /uri</p>
|
||
.
|
||
|
||
.
|
||
[foo][ref[bar]]
|
||
|
||
[ref[bar]]: /uri
|
||
.
|
||
<p>[foo][ref[bar]]</p>
|
||
<p>[ref[bar]]: /uri</p>
|
||
.
|
||
|
||
.
|
||
[[[foo]]]
|
||
|
||
[[[foo]]]: /url
|
||
.
|
||
<p>[[[foo]]]</p>
|
||
<p>[[[foo]]]: /url</p>
|
||
.
|
||
|
||
.
|
||
[foo][ref\[]
|
||
|
||
[ref\[]: /uri
|
||
.
|
||
<p><a href="/uri">foo</a></p>
|
||
.
|
||
|
||
A [collapsed reference link](@collapsed-reference-link)
|
||
consists of a [link label] that [matches] a
|
||
[link reference definition] elsewhere in the
|
||
document, optional [whitespace], and the string `[]`.
|
||
The contents of the first link label are parsed as inlines,
|
||
which are used as the link's text. The link's URI and title are
|
||
provided by the matching reference link definition. Thus,
|
||
`[foo][]` is equivalent to `[foo][foo]`.
|
||
|
||
.
|
||
[foo][]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p><a href="/url" title="title">foo</a></p>
|
||
.
|
||
|
||
.
|
||
[*foo* bar][]
|
||
|
||
[*foo* bar]: /url "title"
|
||
.
|
||
<p><a href="/url" title="title"><em>foo</em> bar</a></p>
|
||
.
|
||
|
||
The link labels are case-insensitive:
|
||
|
||
.
|
||
[Foo][]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p><a href="/url" title="title">Foo</a></p>
|
||
.
|
||
|
||
|
||
As with full reference links, [whitespace] is allowed
|
||
between the two sets of brackets:
|
||
|
||
.
|
||
[foo]
|
||
[]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p><a href="/url" title="title">foo</a></p>
|
||
.
|
||
|
||
A [shortcut reference link](@shortcut-reference-link)
|
||
consists of a [link label] that [matches] a
|
||
[link reference definition] elsewhere in the
|
||
document and is not followed by `[]` or a link label.
|
||
The contents of the first link label are parsed as inlines,
|
||
which are used as the link's text. the link's URI and title
|
||
are provided by the matching link reference definition.
|
||
Thus, `[foo]` is equivalent to `[foo][]`.
|
||
|
||
.
|
||
[foo]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p><a href="/url" title="title">foo</a></p>
|
||
.
|
||
|
||
.
|
||
[*foo* bar]
|
||
|
||
[*foo* bar]: /url "title"
|
||
.
|
||
<p><a href="/url" title="title"><em>foo</em> bar</a></p>
|
||
.
|
||
|
||
.
|
||
[[*foo* bar]]
|
||
|
||
[*foo* bar]: /url "title"
|
||
.
|
||
<p>[<a href="/url" title="title"><em>foo</em> bar</a>]</p>
|
||
.
|
||
|
||
The link labels are case-insensitive:
|
||
|
||
.
|
||
[Foo]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p><a href="/url" title="title">Foo</a></p>
|
||
.
|
||
|
||
A space after the link text should be preserved:
|
||
|
||
.
|
||
[foo] bar
|
||
|
||
[foo]: /url
|
||
.
|
||
<p><a href="/url">foo</a> bar</p>
|
||
.
|
||
|
||
If you just want bracketed text, you can backslash-escape the
|
||
opening bracket to avoid links:
|
||
|
||
.
|
||
\[foo]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p>[foo]</p>
|
||
.
|
||
|
||
Note that this is a link, because a link label ends with the first
|
||
following closing bracket:
|
||
|
||
.
|
||
[foo*]: /url
|
||
|
||
*[foo*]
|
||
.
|
||
<p>*<a href="/url">foo*</a></p>
|
||
.
|
||
|
||
Full references take precedence over shortcut references:
|
||
|
||
.
|
||
[foo][bar]
|
||
|
||
[foo]: /url1
|
||
[bar]: /url2
|
||
.
|
||
<p><a href="/url2">foo</a></p>
|
||
.
|
||
|
||
In the following case `[bar][baz]` is parsed as a reference,
|
||
`[foo]` as normal text:
|
||
|
||
.
|
||
[foo][bar][baz]
|
||
|
||
[baz]: /url
|
||
.
|
||
<p>[foo]<a href="/url">bar</a></p>
|
||
.
|
||
|
||
Here, though, `[foo][bar]` is parsed as a reference, since
|
||
`[bar]` is defined:
|
||
|
||
.
|
||
[foo][bar][baz]
|
||
|
||
[baz]: /url1
|
||
[bar]: /url2
|
||
.
|
||
<p><a href="/url2">foo</a><a href="/url1">baz</a></p>
|
||
.
|
||
|
||
Here `[foo]` is not parsed as a shortcut reference, because it
|
||
is followed by a link label (even though `[bar]` is not defined):
|
||
|
||
.
|
||
[foo][bar][baz]
|
||
|
||
[baz]: /url1
|
||
[foo]: /url2
|
||
.
|
||
<p>[foo]<a href="/url1">bar</a></p>
|
||
.
|
||
|
||
|
||
## Images
|
||
|
||
Syntax for images is like the syntax for links, with one
|
||
difference. Instead of [link text], we have an
|
||
[image description](@image-description). The rules for this are the
|
||
same as for [link text], except that (a) an
|
||
image description starts with `
|
||
.
|
||
<p><img src="/url" alt="foo" title="title" /></p>
|
||
.
|
||
|
||
.
|
||
![foo *bar*]
|
||
|
||
[foo *bar*]: train.jpg "train & tracks"
|
||
.
|
||
<p><img src="train.jpg" alt="foo bar" title="train & tracks" /></p>
|
||
.
|
||
|
||
.
|
||
](/url2)
|
||
.
|
||
<p><img src="/url2" alt="foo bar" /></p>
|
||
.
|
||
|
||
.
|
||
](/url2)
|
||
.
|
||
<p><img src="/url2" alt="foo bar" /></p>
|
||
.
|
||
|
||
Though this spec is concerned with parsing, not rendering, it is
|
||
recommended that in rendering to HTML, only the plain string content
|
||
of the [image description] be used. Note that in
|
||
the above example, the alt attribute's value is `foo bar`, not `foo
|
||
[bar](/url)` or `foo <a href="/url">bar</a>`. Only the plain string
|
||
content is rendered, without formatting.
|
||
|
||
.
|
||
![foo *bar*][]
|
||
|
||
[foo *bar*]: train.jpg "train & tracks"
|
||
.
|
||
<p><img src="train.jpg" alt="foo bar" title="train & tracks" /></p>
|
||
.
|
||
|
||
.
|
||
![foo *bar*][foobar]
|
||
|
||
[FOOBAR]: train.jpg "train & tracks"
|
||
.
|
||
<p><img src="train.jpg" alt="foo bar" title="train & tracks" /></p>
|
||
.
|
||
|
||
.
|
||
|
||
.
|
||
<p><img src="train.jpg" alt="foo" /></p>
|
||
.
|
||
|
||
.
|
||
My 
|
||
.
|
||
<p>My <img src="/path/to/train.jpg" alt="foo bar" title="title" /></p>
|
||
.
|
||
|
||
.
|
||
|
||
.
|
||
<p><img src="url" alt="foo" /></p>
|
||
.
|
||
|
||
.
|
||
|
||
.
|
||
<p><img src="/url" alt="" /></p>
|
||
.
|
||
|
||
Reference-style:
|
||
|
||
.
|
||
![foo] [bar]
|
||
|
||
[bar]: /url
|
||
.
|
||
<p><img src="/url" alt="foo" /></p>
|
||
.
|
||
|
||
.
|
||
![foo] [bar]
|
||
|
||
[BAR]: /url
|
||
.
|
||
<p><img src="/url" alt="foo" /></p>
|
||
.
|
||
|
||
Collapsed:
|
||
|
||
.
|
||
![foo][]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p><img src="/url" alt="foo" title="title" /></p>
|
||
.
|
||
|
||
.
|
||
![*foo* bar][]
|
||
|
||
[*foo* bar]: /url "title"
|
||
.
|
||
<p><img src="/url" alt="foo bar" title="title" /></p>
|
||
.
|
||
|
||
The labels are case-insensitive:
|
||
|
||
.
|
||
![Foo][]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p><img src="/url" alt="Foo" title="title" /></p>
|
||
.
|
||
|
||
As with full reference links, [whitespace] is allowed
|
||
between the two sets of brackets:
|
||
|
||
.
|
||
![foo]
|
||
[]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p><img src="/url" alt="foo" title="title" /></p>
|
||
.
|
||
|
||
Shortcut:
|
||
|
||
.
|
||
![foo]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p><img src="/url" alt="foo" title="title" /></p>
|
||
.
|
||
|
||
.
|
||
![*foo* bar]
|
||
|
||
[*foo* bar]: /url "title"
|
||
.
|
||
<p><img src="/url" alt="foo bar" title="title" /></p>
|
||
.
|
||
|
||
Note that link labels cannot contain unescaped brackets:
|
||
|
||
.
|
||
![[foo]]
|
||
|
||
[[foo]]: /url "title"
|
||
.
|
||
<p>![[foo]]</p>
|
||
<p>[[foo]]: /url "title"</p>
|
||
.
|
||
|
||
The link labels are case-insensitive:
|
||
|
||
.
|
||
![Foo]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p><img src="/url" alt="Foo" title="title" /></p>
|
||
.
|
||
|
||
If you just want bracketed text, you can backslash-escape the
|
||
opening `!` and `[`:
|
||
|
||
.
|
||
\!\[foo]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p>![foo]</p>
|
||
.
|
||
|
||
If you want a link after a literal `!`, backslash-escape the
|
||
`!`:
|
||
|
||
.
|
||
\![foo]
|
||
|
||
[foo]: /url "title"
|
||
.
|
||
<p>!<a href="/url" title="title">foo</a></p>
|
||
.
|
||
|
||
## Autolinks
|
||
|
||
[Autolink](@autolink)s are absolute URIs and email addresses inside
|
||
`<` and `>`. They are parsed as links, with the URL or email address
|
||
as the link label.
|
||
|
||
A [URI autolink](@uri-autolink) consists of `<`, followed by an
|
||
[absolute URI] not containing `<`, followed by `>`. It is parsed as
|
||
a link to the URI, with the URI as the link's label.
|
||
|
||
An [absolute URI](@absolute-uri),
|
||
for these purposes, consists of a [scheme] followed by a colon (`:`)
|
||
followed by zero or more characters other than ASCII
|
||
[whitespace] and control characters, `<`, and `>`. If
|
||
the URI includes these characters, you must use percent-encoding
|
||
(e.g. `%20` for a space).
|
||
|
||
The following [schemes](@scheme)
|
||
are recognized (case-insensitive):
|
||
`coap`, `doi`, `javascript`, `aaa`, `aaas`, `about`, `acap`, `cap`,
|
||
`cid`, `crid`, `data`, `dav`, `dict`, `dns`, `file`, `ftp`, `geo`, `go`,
|
||
`gopher`, `h323`, `http`, `https`, `iax`, `icap`, `im`, `imap`, `info`,
|
||
`ipp`, `iris`, `iris.beep`, `iris.xpc`, `iris.xpcs`, `iris.lwz`, `ldap`,
|
||
`mailto`, `mid`, `msrp`, `msrps`, `mtqp`, `mupdate`, `news`, `nfs`,
|
||
`ni`, `nih`, `nntp`, `opaquelocktoken`, `pop`, `pres`, `rtsp`,
|
||
`service`, `session`, `shttp`, `sieve`, `sip`, `sips`, `sms`, `snmp`,`
|
||
soap.beep`, `soap.beeps`, `tag`, `tel`, `telnet`, `tftp`, `thismessage`,
|
||
`tn3270`, `tip`, `tv`, `urn`, `vemmi`, `ws`, `wss`, `xcon`,
|
||
`xcon-userid`, `xmlrpc.beep`, `xmlrpc.beeps`, `xmpp`, `z39.50r`,
|
||
`z39.50s`, `adiumxtra`, `afp`, `afs`, `aim`, `apt`,` attachment`, `aw`,
|
||
`beshare`, `bitcoin`, `bolo`, `callto`, `chrome`,` chrome-extension`,
|
||
`com-eventbrite-attendee`, `content`, `cvs`,` dlna-playsingle`,
|
||
`dlna-playcontainer`, `dtn`, `dvb`, `ed2k`, `facetime`, `feed`,
|
||
`finger`, `fish`, `gg`, `git`, `gizmoproject`, `gtalk`, `hcp`, `icon`,
|
||
`ipn`, `irc`, `irc6`, `ircs`, `itms`, `jar`, `jms`, `keyparc`, `lastfm`,
|
||
`ldaps`, `magnet`, `maps`, `market`,` message`, `mms`, `ms-help`,
|
||
`msnim`, `mumble`, `mvn`, `notes`, `oid`, `palm`, `paparazzi`,
|
||
`platform`, `proxy`, `psyc`, `query`, `res`, `resource`, `rmi`, `rsync`,
|
||
`rtmp`, `secondlife`, `sftp`, `sgn`, `skype`, `smb`, `soldat`,
|
||
`spotify`, `ssh`, `steam`, `svn`, `teamspeak`, `things`, `udp`,
|
||
`unreal`, `ut2004`, `ventrilo`, `view-source`, `webcal`, `wtai`,
|
||
`wyciwyg`, `xfire`, `xri`, `ymsgr`.
|
||
|
||
Here are some valid autolinks:
|
||
|
||
.
|
||
<http://foo.bar.baz>
|
||
.
|
||
<p><a href="http://foo.bar.baz">http://foo.bar.baz</a></p>
|
||
.
|
||
|
||
.
|
||
<http://foo.bar.baz?q=hello&id=22&boolean>
|
||
.
|
||
<p><a href="http://foo.bar.baz?q=hello&id=22&boolean">http://foo.bar.baz?q=hello&id=22&boolean</a></p>
|
||
.
|
||
|
||
.
|
||
<irc://foo.bar:2233/baz>
|
||
.
|
||
<p><a href="irc://foo.bar:2233/baz">irc://foo.bar:2233/baz</a></p>
|
||
.
|
||
|
||
Uppercase is also fine:
|
||
|
||
.
|
||
<MAILTO:FOO@BAR.BAZ>
|
||
.
|
||
<p><a href="MAILTO:FOO@BAR.BAZ">MAILTO:FOO@BAR.BAZ</a></p>
|
||
.
|
||
|
||
Spaces are not allowed in autolinks:
|
||
|
||
.
|
||
<http://foo.bar/baz bim>
|
||
.
|
||
<p><http://foo.bar/baz bim></p>
|
||
.
|
||
|
||
An [email autolink](@email-autolink)
|
||
consists of `<`, followed by an [email address],
|
||
followed by `>`. The link's label is the email address,
|
||
and the URL is `mailto:` followed by the email address.
|
||
|
||
An [email address](@email-address),
|
||
for these purposes, is anything that matches
|
||
the [non-normative regex from the HTML5
|
||
spec](https://html.spec.whatwg.org/multipage/forms.html#e-mail-state-(type=email)):
|
||
|
||
/^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?
|
||
(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/
|
||
|
||
Examples of email autolinks:
|
||
|
||
.
|
||
<foo@bar.example.com>
|
||
.
|
||
<p><a href="mailto:foo@bar.example.com">foo@bar.example.com</a></p>
|
||
.
|
||
|
||
.
|
||
<foo+special@Bar.baz-bar0.com>
|
||
.
|
||
<p><a href="mailto:foo+special@Bar.baz-bar0.com">foo+special@Bar.baz-bar0.com</a></p>
|
||
.
|
||
|
||
These are not autolinks:
|
||
|
||
.
|
||
<>
|
||
.
|
||
<p><></p>
|
||
.
|
||
|
||
.
|
||
<heck://bing.bong>
|
||
.
|
||
<p><heck://bing.bong></p>
|
||
.
|
||
|
||
.
|
||
< http://foo.bar >
|
||
.
|
||
<p>< http://foo.bar ></p>
|
||
.
|
||
|
||
.
|
||
<foo.bar.baz>
|
||
.
|
||
<p><foo.bar.baz></p>
|
||
.
|
||
|
||
.
|
||
<localhost:5001/foo>
|
||
.
|
||
<p><localhost:5001/foo></p>
|
||
.
|
||
|
||
.
|
||
http://example.com
|
||
.
|
||
<p>http://example.com</p>
|
||
.
|
||
|
||
.
|
||
foo@bar.example.com
|
||
.
|
||
<p>foo@bar.example.com</p>
|
||
.
|
||
|
||
## Raw HTML
|
||
|
||
Text between `<` and `>` that looks like an HTML tag is parsed as a
|
||
raw HTML tag and will be rendered in HTML without escaping.
|
||
Tag and attribute names are not limited to current HTML tags,
|
||
so custom tags (and even, say, DocBook tags) may be used.
|
||
|
||
Here is the grammar for tags:
|
||
|
||
A [tag name](@tag-name) consists of an ASCII letter
|
||
followed by zero or more ASCII letters or digits.
|
||
|
||
An [attribute](@attribute) consists of [whitespace],
|
||
an [attribute name], and an optional
|
||
[attribute value specification].
|
||
|
||
An [attribute name](@attribute-name)
|
||
consists of an ASCII letter, `_`, or `:`, followed by zero or more ASCII
|
||
letters, digits, `_`, `.`, `:`, or `-`. (Note: This is the XML
|
||
specification restricted to ASCII. HTML5 is laxer.)
|
||
|
||
An [attribute value specification](@attribute-value-specification)
|
||
consists of optional [whitespace],
|
||
a `=` character, optional [whitespace], and an [attribute
|
||
value].
|
||
|
||
An [attribute value](@attribute-value)
|
||
consists of an [unquoted attribute value],
|
||
a [single-quoted attribute value], or a [double-quoted attribute value].
|
||
|
||
An [unquoted attribute value](@unquoted-attribute-value)
|
||
is a nonempty string of characters not
|
||
including spaces, `"`, `'`, `=`, `<`, `>`, or `` ` ``.
|
||
|
||
A [single-quoted attribute value](@single-quoted-attribute-value)
|
||
consists of `'`, zero or more
|
||
characters not including `'`, and a final `'`.
|
||
|
||
A [double-quoted attribute value](@double-quoted-attribute-value)
|
||
consists of `"`, zero or more
|
||
characters not including `"`, and a final `"`.
|
||
|
||
An [open tag](@open-tag) consists of a `<` character, a [tag name],
|
||
zero or more [attributes], optional [whitespace], an optional `/`
|
||
character, and a `>` character.
|
||
|
||
A [closing tag](@closing-tag) consists of the string `</`, a
|
||
[tag name], optional [whitespace], and the character `>`.
|
||
|
||
An [HTML comment](@html-comment) consists of `<!--` + *text* + `-->`,
|
||
where *text* does not start with `>` or `->`, does not end with `-`,
|
||
and does not contain `--`. (See the
|
||
[HTML5 spec](http://www.w3.org/TR/html5/syntax.html#comments).)
|
||
|
||
A [processing instruction](@processing-instruction)
|
||
consists of the string `<?`, a string
|
||
of characters not including the string `?>`, and the string
|
||
`?>`.
|
||
|
||
A [declaration](@declaration) consists of the
|
||
string `<!`, a name consisting of one or more uppercase ASCII letters,
|
||
[whitespace], a string of characters not including the
|
||
character `>`, and the character `>`.
|
||
|
||
A [CDATA section](@cdata-section) consists of
|
||
the string `<![CDATA[`, a string of characters not including the string
|
||
`]]>`, and the string `]]>`.
|
||
|
||
An [HTML tag](@html-tag) consists of an [open tag], a [closing tag],
|
||
an [HTML comment], a [processing instruction], a [declaration],
|
||
or a [CDATA section].
|
||
|
||
Here are some simple open tags:
|
||
|
||
.
|
||
<a><bab><c2c>
|
||
.
|
||
<p><a><bab><c2c></p>
|
||
.
|
||
|
||
Empty elements:
|
||
|
||
.
|
||
<a/><b2/>
|
||
.
|
||
<p><a/><b2/></p>
|
||
.
|
||
|
||
[Whitespace] is allowed:
|
||
|
||
.
|
||
<a /><b2
|
||
data="foo" >
|
||
.
|
||
<p><a /><b2
|
||
data="foo" ></p>
|
||
.
|
||
|
||
With attributes:
|
||
|
||
.
|
||
<a foo="bar" bam = 'baz <em>"</em>'
|
||
_boolean zoop:33=zoop:33 />
|
||
.
|
||
<p><a foo="bar" bam = 'baz <em>"</em>'
|
||
_boolean zoop:33=zoop:33 /></p>
|
||
.
|
||
|
||
Illegal tag names, not parsed as HTML:
|
||
|
||
.
|
||
<33> <__>
|
||
.
|
||
<p><33> <__></p>
|
||
.
|
||
|
||
Illegal attribute names:
|
||
|
||
.
|
||
<a h*#ref="hi">
|
||
.
|
||
<p><a h*#ref="hi"></p>
|
||
.
|
||
|
||
Illegal attribute values:
|
||
|
||
.
|
||
<a href="hi'> <a href=hi'>
|
||
.
|
||
<p><a href="hi'> <a href=hi'></p>
|
||
.
|
||
|
||
Illegal [whitespace]:
|
||
|
||
.
|
||
< a><
|
||
foo><bar/ >
|
||
.
|
||
<p>< a><
|
||
foo><bar/ ></p>
|
||
.
|
||
|
||
Missing [whitespace]:
|
||
|
||
.
|
||
<a href='bar'title=title>
|
||
.
|
||
<p><a href='bar'title=title></p>
|
||
.
|
||
|
||
Closing tags:
|
||
|
||
.
|
||
</a>
|
||
</foo >
|
||
.
|
||
<p></a>
|
||
</foo ></p>
|
||
.
|
||
|
||
Illegal attributes in closing tag:
|
||
|
||
.
|
||
</a href="foo">
|
||
.
|
||
<p></a href="foo"></p>
|
||
.
|
||
|
||
Comments:
|
||
|
||
.
|
||
foo <!-- this is a
|
||
comment - with hyphen -->
|
||
.
|
||
<p>foo <!-- this is a
|
||
comment - with hyphen --></p>
|
||
.
|
||
|
||
.
|
||
foo <!-- not a comment -- two hyphens -->
|
||
.
|
||
<p>foo <!-- not a comment -- two hyphens --></p>
|
||
.
|
||
|
||
Not comments:
|
||
|
||
.
|
||
foo <!--> foo -->
|
||
|
||
foo <!-- foo--->
|
||
.
|
||
<p>foo <!--> foo --></p>
|
||
<p>foo <!-- foo---></p>
|
||
.
|
||
|
||
Processing instructions:
|
||
|
||
.
|
||
foo <?php echo $a; ?>
|
||
.
|
||
<p>foo <?php echo $a; ?></p>
|
||
.
|
||
|
||
Declarations:
|
||
|
||
.
|
||
foo <!ELEMENT br EMPTY>
|
||
.
|
||
<p>foo <!ELEMENT br EMPTY></p>
|
||
.
|
||
|
||
CDATA sections:
|
||
|
||
.
|
||
foo <![CDATA[>&<]]>
|
||
.
|
||
<p>foo <![CDATA[>&<]]></p>
|
||
.
|
||
|
||
Entities are preserved in HTML attributes:
|
||
|
||
.
|
||
<a href="ö">
|
||
.
|
||
<p><a href="ö"></p>
|
||
.
|
||
|
||
Backslash escapes do not work in HTML attributes:
|
||
|
||
.
|
||
<a href="\*">
|
||
.
|
||
<p><a href="\*"></p>
|
||
.
|
||
|
||
.
|
||
<a href="\"">
|
||
.
|
||
<p><a href="""></p>
|
||
.
|
||
|
||
## Hard line breaks
|
||
|
||
A line break (not in a code span or HTML tag) that is preceded
|
||
by two or more spaces and does not occur at the end of a block
|
||
is parsed as a [hard line break](@hard-line-break) (rendered
|
||
in HTML as a `<br />` tag):
|
||
|
||
.
|
||
foo
|
||
baz
|
||
.
|
||
<p>foo<br />
|
||
baz</p>
|
||
.
|
||
|
||
For a more visible alternative, a backslash before the
|
||
[line ending] may be used instead of two spaces:
|
||
|
||
.
|
||
foo\
|
||
baz
|
||
.
|
||
<p>foo<br />
|
||
baz</p>
|
||
.
|
||
|
||
More than two spaces can be used:
|
||
|
||
.
|
||
foo
|
||
baz
|
||
.
|
||
<p>foo<br />
|
||
baz</p>
|
||
.
|
||
|
||
Leading spaces at the beginning of the next line are ignored:
|
||
|
||
.
|
||
foo
|
||
bar
|
||
.
|
||
<p>foo<br />
|
||
bar</p>
|
||
.
|
||
|
||
.
|
||
foo\
|
||
bar
|
||
.
|
||
<p>foo<br />
|
||
bar</p>
|
||
.
|
||
|
||
Line breaks can occur inside emphasis, links, and other constructs
|
||
that allow inline content:
|
||
|
||
.
|
||
*foo
|
||
bar*
|
||
.
|
||
<p><em>foo<br />
|
||
bar</em></p>
|
||
.
|
||
|
||
.
|
||
*foo\
|
||
bar*
|
||
.
|
||
<p><em>foo<br />
|
||
bar</em></p>
|
||
.
|
||
|
||
Line breaks do not occur inside code spans
|
||
|
||
.
|
||
`code
|
||
span`
|
||
.
|
||
<p><code>code span</code></p>
|
||
.
|
||
|
||
.
|
||
`code\
|
||
span`
|
||
.
|
||
<p><code>code\ span</code></p>
|
||
.
|
||
|
||
or HTML tags:
|
||
|
||
.
|
||
<a href="foo
|
||
bar">
|
||
.
|
||
<p><a href="foo
|
||
bar"></p>
|
||
.
|
||
|
||
.
|
||
<a href="foo\
|
||
bar">
|
||
.
|
||
<p><a href="foo\
|
||
bar"></p>
|
||
.
|
||
|
||
Hard line breaks are for separating inline content within a block.
|
||
Neither syntax for hard line breaks works at the end of a paragraph or
|
||
other block element:
|
||
|
||
.
|
||
foo\
|
||
.
|
||
<p>foo\</p>
|
||
.
|
||
|
||
.
|
||
foo
|
||
.
|
||
<p>foo</p>
|
||
.
|
||
|
||
.
|
||
### foo\
|
||
.
|
||
<h3>foo\</h3>
|
||
.
|
||
|
||
.
|
||
### foo
|
||
.
|
||
<h3>foo</h3>
|
||
.
|
||
|
||
## Soft line breaks
|
||
|
||
A regular line break (not in a code span or HTML tag) that is not
|
||
preceded by two or more spaces is parsed as a softbreak. (A
|
||
softbreak may be rendered in HTML either as a
|
||
[line ending] or as a space. The result will be the same
|
||
in browsers. In the examples here, a [line ending] will be used.)
|
||
|
||
.
|
||
foo
|
||
baz
|
||
.
|
||
<p>foo
|
||
baz</p>
|
||
.
|
||
|
||
Spaces at the end of the line and beginning of the next line are
|
||
removed:
|
||
|
||
.
|
||
foo
|
||
baz
|
||
.
|
||
<p>foo
|
||
baz</p>
|
||
.
|
||
|
||
A conforming parser may render a soft line break in HTML either as a
|
||
line break or as a space.
|
||
|
||
A renderer may also provide an option to render soft line breaks
|
||
as hard line breaks.
|
||
|
||
## Textual content
|
||
|
||
Any characters not given an interpretation by the above rules will
|
||
be parsed as plain textual content.
|
||
|
||
.
|
||
hello $.;'there
|
||
.
|
||
<p>hello $.;'there</p>
|
||
.
|
||
|
||
.
|
||
Foo χρῆν
|
||
.
|
||
<p>Foo χρῆν</p>
|
||
.
|
||
|
||
Internal spaces are preserved verbatim:
|
||
|
||
.
|
||
Multiple spaces
|
||
.
|
||
<p>Multiple spaces</p>
|
||
.
|
||
|
||
<!-- END TESTS -->
|
||
|
||
# Appendix A: A parsing strategy {-}
|
||
|
||
## Overview {-}
|
||
|
||
Parsing has two phases:
|
||
|
||
1. In the first phase, lines of input are consumed and the block
|
||
structure of the document---its division into paragraphs, block quotes,
|
||
list items, and so on---is constructed. Text is assigned to these
|
||
blocks but not parsed. Link reference definitions are parsed and a
|
||
map of links is constructed.
|
||
|
||
2. In the second phase, the raw text contents of paragraphs and headers
|
||
are parsed into sequences of Markdown inline elements (strings,
|
||
code spans, links, emphasis, and so on), using the map of link
|
||
references constructed in phase 1.
|
||
|
||
## The document tree {-}
|
||
|
||
At each point in processing, the document is represented as a tree of
|
||
**blocks**. The root of the tree is a `document` block. The `document`
|
||
may have any number of other blocks as **children**. These children
|
||
may, in turn, have other blocks as children. The last child of a block
|
||
is normally considered **open**, meaning that subsequent lines of input
|
||
can alter its contents. (Blocks that are not open are **closed**.)
|
||
Here, for example, is a possible document tree, with the open blocks
|
||
marked by arrows:
|
||
|
||
``` tree
|
||
-> document
|
||
-> block_quote
|
||
paragraph
|
||
"Lorem ipsum dolor\nsit amet."
|
||
-> list (type=bullet tight=true bullet_char=-)
|
||
list_item
|
||
paragraph
|
||
"Qui *quodsi iracundia*"
|
||
-> list_item
|
||
-> paragraph
|
||
"aliquando id"
|
||
```
|
||
|
||
## How source lines alter the document tree {-}
|
||
|
||
Each line that is processed has an effect on this tree. The line is
|
||
analyzed and, depending on its contents, the document may be altered
|
||
in one or more of the following ways:
|
||
|
||
1. One or more open blocks may be closed.
|
||
2. One or more new blocks may be created as children of the
|
||
last open block.
|
||
3. Text may be added to the last (deepest) open block remaining
|
||
on the tree.
|
||
|
||
Once a line has been incorporated into the tree in this way,
|
||
it can be discarded, so input can be read in a stream.
|
||
|
||
We can see how this works by considering how the tree above is
|
||
generated by four lines of Markdown:
|
||
|
||
``` markdown
|
||
> Lorem ipsum dolor
|
||
sit amet.
|
||
> - Qui *quodsi iracundia*
|
||
> - aliquando id
|
||
```
|
||
|
||
At the outset, our document model is just
|
||
|
||
``` tree
|
||
-> document
|
||
```
|
||
|
||
The first line of our text,
|
||
|
||
``` markdown
|
||
> Lorem ipsum dolor
|
||
```
|
||
|
||
causes a `block_quote` block to be created as a child of our
|
||
open `document` block, and a `paragraph` block as a child of
|
||
the `block_quote`. Then the text is added to the last open
|
||
block, the `paragraph`:
|
||
|
||
``` tree
|
||
-> document
|
||
-> block_quote
|
||
-> paragraph
|
||
"Lorem ipsum dolor"
|
||
```
|
||
|
||
The next line,
|
||
|
||
``` markdown
|
||
sit amet.
|
||
```
|
||
|
||
is a "lazy continuation" of the open `paragraph`, so it gets added
|
||
to the paragraph's text:
|
||
|
||
``` tree
|
||
-> document
|
||
-> block_quote
|
||
-> paragraph
|
||
"Lorem ipsum dolor\nsit amet."
|
||
```
|
||
|
||
The third line,
|
||
|
||
``` markdown
|
||
> - Qui *quodsi iracundia*
|
||
```
|
||
|
||
causes the `paragraph` block to be closed, and a new `list` block
|
||
opened as a child of the `block_quote`. A `list_item` is also
|
||
added as a child of the `list`, and a `paragraph` as a child of
|
||
the `list_item`. The text is then added to the new `paragraph`:
|
||
|
||
``` tree
|
||
-> document
|
||
-> block_quote
|
||
paragraph
|
||
"Lorem ipsum dolor\nsit amet."
|
||
-> list (type=bullet tight=true bullet_char=-)
|
||
-> list_item
|
||
-> paragraph
|
||
"Qui *quodsi iracundia*"
|
||
```
|
||
|
||
The fourth line,
|
||
|
||
``` markdown
|
||
> - aliquando id
|
||
```
|
||
|
||
causes the `list_item` (and its child the `paragraph`) to be closed,
|
||
and a new `list_item` opened up as child of the `list`. A `paragraph`
|
||
is added as a child of the new `list_item`, to contain the text.
|
||
We thus obtain the final tree:
|
||
|
||
``` tree
|
||
-> document
|
||
-> block_quote
|
||
paragraph
|
||
"Lorem ipsum dolor\nsit amet."
|
||
-> list (type=bullet tight=true bullet_char=-)
|
||
list_item
|
||
paragraph
|
||
"Qui *quodsi iracundia*"
|
||
-> list_item
|
||
-> paragraph
|
||
"aliquando id"
|
||
```
|
||
|
||
## From block structure to the final document {-}
|
||
|
||
Once all of the input has been parsed, all open blocks are closed.
|
||
|
||
We then "walk the tree," visiting every node, and parse raw
|
||
string contents of paragraphs and headers as inlines. At this
|
||
point we have seen all the link reference definitions, so we can
|
||
resolve reference links as we go.
|
||
|
||
``` tree
|
||
document
|
||
block_quote
|
||
paragraph
|
||
str "Lorem ipsum dolor"
|
||
softbreak
|
||
str "sit amet."
|
||
list (type=bullet tight=true bullet_char=-)
|
||
list_item
|
||
paragraph
|
||
str "Qui "
|
||
emph
|
||
str "quodsi iracundia"
|
||
list_item
|
||
paragraph
|
||
str "aliquando id"
|
||
```
|
||
|
||
Notice how the [line ending] in the first paragraph has
|
||
been parsed as a `softbreak`, and the asterisks in the first list item
|
||
have become an `emph`.
|
||
|
||
The document can be rendered as HTML, or in any other format, given
|
||
an appropriate renderer.
|