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 --- title: CommonMark Spec author: John MacFarlane version: 0.27 date: '2016-11-18' license: '[CC-BY-SA 4.0](http://creativecommons.org/licenses/by-sa/4.0/)' ... # Introduction ## What is Markdown? Markdown is a plain text format for writing structured documents, based on conventions used for indicating formatting in email and usenet posts. It was developed in 2004 by John Gruber, who wrote the first Markdown-to-HTML converter in Perl, and it soon became ubiquitous. In the next decade, dozens of implementations were developed in many languages. Some extended the original Markdown syntax with conventions for footnotes, tables, and other document elements. Some allowed Markdown documents to be rendered in formats other than HTML. Websites like Reddit, StackOverflow, and GitHub had millions of people using Markdown. And Markdown started to be used beyond the web, to author books, articles, slide shows, letters, and lecture notes. What distinguishes Markdown from many other lightweight markup syntaxes, which are often easier to write, is its readability. As Gruber writes: > The overriding design goal for Markdown's formatting syntax is > to make it as readable as possible. The idea is that a > Markdown-formatted document should be publishable as-is, as > plain text, without looking like it's been marked up with tags > or formatting instructions. > () The point can be illustrated by comparing a sample of [AsciiDoc](http://www.methods.co.nz/asciidoc/) with an equivalent sample of Markdown. Here is a sample of AsciiDoc from the AsciiDoc manual:  1. List item one. + List item one continued with a second paragraph followed by an Indented block. + ................. $ls *.sh$ mv *.sh ~/tmp ................. + List item continued with a third paragraph. 2. List item two continued with an open block. + -- This paragraph is part of the preceding list item. a. This list is nested and does not require explicit item continuation. + This paragraph is part of the preceding list item. b. List item b. This paragraph belongs to item two of the outer list. --  And here is the equivalent in Markdown:  1. List item one. List item one continued with a second paragraph followed by an Indented block. $ls *.sh$ mv *.sh ~/tmp List item continued with a third paragraph. 2. List item two continued with an open block. This paragraph is part of the preceding list item. 1. This list is nested and does not require explicit item continuation. This paragraph is part of the preceding list item. 2. List item b. This paragraph belongs to item two of the outer list.  The AsciiDoc version is, arguably, easier to write. You don't need to worry about indentation. But the Markdown version is much easier to read. The nesting of list items is apparent to the eye in the source, not just in the processed document. ## Why is a spec needed? John Gruber's [canonical description of Markdown's syntax](http://daringfireball.net/projects/markdown/syntax) does not specify the syntax unambiguously. Here are some examples of questions it does not answer: 1. How much indentation is needed for a sublist? The spec says that continuation paragraphs need to be indented four spaces, but is not fully explicit about sublists. It is natural to think that they, too, must be indented four spaces, but Markdown.pl does not require that. This is hardly a "corner case," and divergences between implementations on this issue often lead to surprises for users in real documents. (See [this comment by John Gruber](http://article.gmane.org/gmane.text.markdown.general/1997).) 2. Is a blank line needed before a block quote or heading? Most implementations do not require the blank line. However, this can lead to unexpected results in hard-wrapped text, and also to ambiguities in parsing (note that some implementations put the heading inside the blockquote, while others do not). (John Gruber has also spoken [in favor of requiring the blank lines](http://article.gmane.org/gmane.text.markdown.general/2146).) 3. Is a blank line needed before an indented code block? (Markdown.pl requires it, but this is not mentioned in the documentation, and some implementations do not require it.)  markdown paragraph code?  4. What is the exact rule for determining when list items get wrapped in 

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

import Text.HTML.TagSoup

main :: IO ()
main = print \$ parseTags tags

okay

 A script tag (type 1):  example okay .

okay

 A style tag (type 1):  example okay .

okay

 If there is no matching end tag, the block will end at the end of the document (or the enclosing [block quote][block quotes] or [list item][list items]):  example *foo* .

foo

  example *bar* *baz* . *bar*

baz

 Note that anything on the last line after the end tag will be included in the [HTML block]:  example 1. *bar* . 1. *bar*  A comment (type 2):  example okay .

okay

 A processing instruction (type 3):  example '; ?> okay . '; ?>

okay

 A declaration (type 4):  example .  CDATA (type 5):  example okay .

okay

 The opening tag can be indented 1-3 spaces, but not 4:  example .
<!-- foo -->
  example
.
<div>
 An HTML block of types 1--6 can interrupt a paragraph, and need not be preceded by a blank line.  example Foo
bar
.

Foo

bar
 However, a following blank line is needed, except at the end of a document, and except for blocks of types 1--5, above:  example
bar
*foo* .
bar
*foo*  HTML blocks of type 7 cannot interrupt a paragraph:  example Foo baz .

Foo baz

 This rule differs from John Gruber's original Markdown syntax specification, which says: > The only restrictions are that block-level HTML elements — > e.g. 
, , 
, 

, etc. — must be separated from > surrounding content by blank lines, and the start and end tags of the > block should not be indented with tabs or spaces. In some ways Gruber's rule is more restrictive than the one given here: - It requires that an HTML block be preceded by a blank line. - It does not allow the start tag to be indented. - It requires a matching end tag, which it also does not allow to be indented. Most Markdown implementations (including some of Gruber's own) do not respect all of these restrictions. There is one respect, however, in which Gruber's rule is more liberal than the one given here, since it allows blank lines to occur inside an HTML block. There are two reasons for disallowing them here. First, it removes the need to parse balanced tags, which is expensive and can require backtracking from the end of the document if no matching end tag is found. Second, it provides a very simple and flexible way of including Markdown content inside HTML tags: simply separate the Markdown from the HTML using blank lines: Compare:  example

*Emphasized* text.
.

Emphasized text.

  example
*Emphasized* text.
.
*Emphasized* text.
 Some Markdown implementations have adopted a convention of interpreting content inside tags as text if the open tag has the attribute markdown=1. The rule given above seems a simpler and more elegant way of achieving the same expressive power, which is also much simpler to parse. The main potential drawback is that one can no longer paste HTML blocks into Markdown documents with 100% reliability. However, *in most cases* this will work fine, because the blank lines in HTML are usually followed by HTML block tags. For example:  example
Hi
.
Hi
 There are problems, however, if the inner tags are indented *and* separated by spaces, as then they will be interpreted as an indented code block:  example
Hi
.
<td>
Hi
</td>
 Fortunately, blank lines are usually not necessary and can be deleted. The exception is inside 
tags, but as described
above, raw HTML blocks starting with 
*can* contain blank
lines.

consists of a [link label], indented up to three spaces, followed
by a colon (:), optional [whitespace] (including up to one
optional [whitespace] (including up to one
[line ending]), and an optional [link
title], which if it is present must be separated
from the [link destination] by [whitespace].
No further [non-whitespace characters] may occur on the line.

does not correspond to a structural element of a document.  Instead, it
defines a label which can be used in [reference links]
and reference-style [images] elsewhere in the document.  [Link
reference definitions] can come either before or after the links that use
them.

 example
[foo]: /url "title"

[foo]
.

foo

  example [foo]: /url 'the title' [foo] .

foo

  example [Foo*bar\]]:my_(url) 'title (with parens)' [Foo*bar\]] .

Foo*bar]

  example [Foo bar]: 'title' [Foo bar] .

Foo bar

 The title may extend over multiple lines:  example [foo]: /url ' title line1 line2 ' [foo] .

foo

 However, it may not contain a [blank line]:  example [foo]: /url 'title with blank line' [foo] .

[foo]: /url 'title

with blank line'

[foo]

 The title may be omitted:  example [foo]: /url [foo] .

foo

 The link destination may not be omitted:  example [foo]: [foo] .

[foo]:

[foo]

 Both title and destination can contain backslash escapes and literal backslashes:  example [foo]: /url\bar\*baz "foo\"bar\baz" [foo] .

foo

 A link can come before its corresponding definition:  example [foo] [foo]: url .

foo

 If there are several matching definitions, the first one takes precedence:  example [foo] [foo]: first [foo]: second .

foo

 As noted in the section on [Links], matching of labels is case-insensitive (see [matches]).  example [FOO]: /url [Foo] .

Foo

  example [ΑΓΩ]: /φου [αγω] .

αγω

 Here is a link reference definition with no corresponding link. It contributes nothing to the document.  example [foo]: /url .  Here is another one:  example [ foo ]: /url bar .

bar

 This is not a link reference definition, because there are [non-whitespace characters] after the title:  example [foo]: /url "title" ok .

[foo]: /url "title" ok

 This is a link reference definition, but it has no title:  example [foo]: /url "title" ok .

"title" ok

 This is not a link reference definition, because it is indented four spaces:  example [foo]: /url "title" [foo] .
[foo]: /url "title"

[foo]

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

[foo]

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

Foo [bar]: /baz

[bar]

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

Foo

bar

 Several [link reference definitions] can occur one after another, without intervening blank lines.  example [foo]: /foo-url "foo" [bar]: /bar-url "bar" [baz]: /baz-url [foo], [bar], [baz] .

foo, bar, baz

 [Link reference definitions] can occur inside block containers, like lists and block quotations. They affect the entire document, not just the container in which they are defined:  example [foo] > [foo]: /url .

foo

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

aaa

bbb

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

aaa bbb

ccc ddd

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

aaa

bbb

 Leading spaces are skipped:  example aaa bbb .

aaa bbb

 Lines after the first may be indented any amount, since indented code blocks cannot interrupt paragraphs.  example aaa bbb ccc .

aaa bbb ccc

 However, the first line may be indented at most three spaces, or an indented code block will be triggered:  example aaa bbb .

aaa bbb

  example aaa bbb .
aaa

bbb

 Final spaces are stripped before inline parsing, so a paragraph that ends with two or more spaces will not end with a [hard line break]:  example aaa bbb .

aaa
bbb

 ## Blank lines [Blank lines] between block-level elements are ignored, except for the role they play in determining whether a [list] is [tight] or [loose]. Blank lines at the beginning and end of the document are also ignored.  example aaa # aaa .

aaa

aaa

 # Container blocks A [container block] is a block that has other blocks as its contents. There are two basic kinds of container blocks: [block quotes] and [list items]. [Lists] are meta-containers for [list items]. We define the syntax for container blocks recursively. The general form of the definition is: > If X is a sequence of blocks, then the result of > transforming X in such-and-such a way is a container of type Y > with these blocks as its content. So, we explain what counts as a block quote or list item by explaining how these can be *generated* from their contents. This should suffice to define the syntax, although it does not give a recipe for *parsing* these constructions. (A recipe is provided below in the section entitled [A parsing strategy](#appendix-a-parsing-strategy).) ## Block quotes A [block quote marker](@) consists of 0-3 spaces of initial indent, plus (a) the character > together with a following space, or (b) a single character > not followed by a space. The following rules define [block quotes]: 1. **Basic case.** If a string of lines *Ls* constitute a sequence of blocks *Bs*, then the result of prepending a [block quote marker] to the beginning of each line in *Ls* is a [block quote](#block-quotes) containing *Bs*. 2. **Laziness.** If a string of lines *Ls* constitute a [block quote](#block-quotes) with contents *Bs*, then the result of deleting the initial [block quote marker] from one or more lines in which the next [non-whitespace character] after the [block quote marker] is [paragraph continuation text] is a block quote with *Bs* as its content. [Paragraph continuation text](@) 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:  example > # Foo > bar > baz .

Foo

bar baz

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

Foo

bar baz

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

Foo

bar baz

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

Foo

bar baz

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

bar baz foo

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

foo

 Similarly, if we omit the >  in the second line of  markdown > - foo > - bar  then the block quote ends after the first line:  example > - foo - bar .
• foo
• bar
 For the same reason, we can't omit the >  in front of subsequent lines of an indented or fenced code block:  example > foo bar .
foo
bar
  example >  foo  .

foo

 Note that in the following case, we have a [lazy continuation line]:  example > foo - bar .

foo - bar

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

foo

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

foo

bar

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

foo bar

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

foo

bar

 Block quotes can interrupt paragraphs:  example foo > bar .

foo

bar

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

aaa

bbb

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

bar baz

  example > bar baz .

bar

baz

  example > bar > baz .

bar

baz

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

foo bar

  example >>> foo > bar >>baz .

foo bar baz

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

not code

 ## List items A [list marker](@) is a [bullet list marker] or an [ordered list marker]. A [bullet list marker](@) is a -, +, or * character. An [ordered list marker](@) is a sequence of 1--9 arabic digits (0-9), followed by either a . character or a ) character. (The reason for the length limit is that with 10 digits we start seeing integer overflows in some browsers.) The following rules define [list items]: 1. **Basic case.** If a sequence of lines *Ls* constitute a sequence of blocks *Bs* starting with a [non-whitespace character] and not separated from each other by more than one blank line, and *M* is a list marker of width *W* followed by 1 ≤ *N* ≤ 4 spaces, then the result of prepending *M* and the following spaces to the first line of *Ls*, and indenting subsequent lines of *Ls* by *W + N* spaces, is a list item with *Bs* as its contents. The type of the list item (bullet or ordered) is determined by the type of its list marker. If the list item is ordered, then it is also assigned a start number, based on the ordered list marker. Exceptions: When the first list item in a [list] interrupts a paragraph---that is, when it starts on a line that would otherwise count as [paragraph continuation text]---then (a) the lines *Ls* must not begin with a blank line, and (b) if the list item is ordered, the start number must be 1. For example, let *Ls* be the lines  example A paragraph with two lines. indented code > A block quote. .

A paragraph with two lines.

indented code

A block quote.

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

indented code

A block quote.

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

two

  example - one two .
• one

two

  example - one two .
• one
two
  example - one two .
• one

two

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

two

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

two

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

-one

2.two

 A list item may contain blocks that are separated by more than one blank line.  example - foo bar .
• foo

bar

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

bar

baz

bam

 A list item that contains an indented code block will preserve empty lines within the code block verbatim.  example - Foo bar baz .
• Foo

bar

baz

 Note that ordered list start numbers must be nine digits or less:  example 123456789. ok .
1. ok
  example 1234567890. not ok .

1234567890. not ok

 A start number may begin with 0s:  example 0. ok .
1. ok
  example 003. ok .
1. ok
 A start number may not be negative:  example -1. not ok .

-1. not ok

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

bar

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

bar

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

paragraph

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

paragraph

more code

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

paragraph

more code

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

foo

bar

  example - foo bar .
• foo

bar

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

bar

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

• baz

 When the list item starts with a blank line, the number of spaces following the list marker doesn't change the required indentation:  example - foo .
• foo
 A list item can begin with at most one blank line. In the following example, foo is not part of the list item:  example - foo .

foo

 Here is an empty bullet list item:  example - foo - - bar .
• foo
• bar
 It does not matter whether there are spaces following the [list marker]:  example - foo - - bar .
• foo
• bar
 Here is an empty ordered list item:  example 1. foo 2. 3. bar .
1. foo
2. bar
 A list may start or end with an empty list item:  example * .
 However, an empty list item cannot interrupt a paragraph:  example foo * foo 1. .

foo *

foo 1.

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

indented code

A block quote.

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

indented code

A block quote.

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

indented code

A block quote.

 Four spaces indent gives a code block:  example 1. A paragraph with two lines. indented code > A block quote. .
1.  A paragraph
with two lines.

indented code

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

indented code

A block quote.

 Indentation can be partially deleted:  example 1. A paragraph with two lines. .
1. A paragraph with two lines.
 These examples show how laziness can work in nested structures:  example > 1. > Blockquote continued here. .
1. Blockquote continued here.

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

 6. **That's all.** Nothing that is not counted as a list item by rules #1--5 counts as a [list item](#list-items). The rules for sublists follow from the general rules above. A sublist must be indented the same number of spaces a paragraph would need to be in order to be included in the list item. So, in this case we need two spaces indent:  example - foo - bar - baz - boo .
• foo
• bar
• baz
• boo
 One is not enough:  example - foo - bar - baz - boo .
• foo
• bar
• baz
• boo
 Here we need four, because the list marker is wider:  example 10) foo - bar .
1. foo
• bar
 Three is not enough:  example 10) foo - bar .
1. foo
• bar
 A list may be the first block in a list item:  example - - foo .
• foo
  example 1. - 2. foo .
1. foo
 A list item can contain a heading:  example - # Foo - Bar --- baz .
• Foo

• Bar

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

bar

• baz
 as the four-space rule demands, rather than a single list,  html
• foo

bar

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

two

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

two

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

tags, while paragraphs in a tight list are not.) Changing the bullet or ordered list delimiter starts a new list:  example - foo - bar + baz .

• foo
• bar
• baz
  example 1. foo 2. bar 3) baz .
1. foo
2. bar
1. baz
 In CommonMark, a list can interrupt a paragraph. That is, no blank line is needed to separate a paragraph from a following list:  example Foo - bar - baz .

Foo

• bar
• baz
 Markdown.pl does not allow this, through fear of triggering a list via a numeral in a hard-wrapped line:  markdown The number of windows in my house is 14. The number of doors is 6.  Oddly, though, Markdown.pl *does* allow a blockquote to interrupt a paragraph, even though the same considerations might apply. In CommonMark, we do allow lists to interrupt paragraphs, for two reasons. First, it is natural and not uncommon for people to start lists without blank lines:  markdown I need to buy - new shoes - a coat - a plane ticket  Second, we are attracted to a > [principle of uniformity](@): > if a chunk of text has a certain > meaning, it will continue to have the same meaning when put into a > container block (such as a list item or blockquote). (Indeed, the spec for [list items] and [block quotes] presupposes this principle.) This principle implies that if  markdown * I need to buy - new shoes - a coat - a plane ticket  is a list item containing a paragraph followed by a nested sublist, as all Markdown implementations agree it is (though the paragraph may be rendered without 

tags, since the list is "tight"), then  markdown I need to buy - new shoes - a coat - a plane ticket  by itself should be a paragraph followed by a nested sublist. Since it is well established Markdown practice to allow lists to interrupt paragraphs inside list items, the [principle of uniformity] requires us to allow this outside list items as well. ([reStructuredText](http://docutils.sourceforge.net/rst.html) takes a different approach, requiring blank lines before lists even inside other list items.) In order to solve of unwanted lists in paragraphs with hard-wrapped numerals, we allow only lists starting with 1 to interrupt paragraphs. Thus,  example The number of windows in my house is 14. The number of doors is 6. .

The number of windows in my house is 14. The number of doors is 6.

 We may still get an unintended result in cases like  example The number of windows in my house is 1. The number of doors is 6. .

The number of windows in my house is

1. The number of doors is 6.
 but this rule should prevent most spurious list captures. There can be any number of blank lines between items:  example - foo - bar - baz .