# Rules

This document contains a description of all rules, what they are checking for,
as well as an examples of documents that break the rule and corrected
versions of the examples. Any rule whose heading is struck through is
deprecated, but still provided for backward-compatibility.

## MD001 - Heading levels should only increment by one level at a time

This rule is triggered when you skip heading levels in a markdown document, for
example:

# Heading 1

We skipped out a 2nd level heading in this document

When using multiple heading levels, nested headings should increase by only one
level at a time:

# Heading 1

### Another Heading 3

Rationale: Headings represent the structure of a document and can be confusing

Parameters: level (number; default 1)

Note: MD002 has been deprecated and is disabled by default.

This rule is intended to ensure document headings start at the top level and
is triggered when the first heading in the document isn't an h1 heading:

## This isn't an H1 heading

### Another heading

# Start with an H1 heading

## Then use an H2 for subsections

Note: The level parameter can be used to change the top level (ex: to h2) in
cases where an h1 is added externally.

Rationale: The top level heading often acts as the title of a document. More

Parameters: style ("consistent", "atx", "atx_closed", "setext",
"setext_with_atx", "setext_with_atx_closed"; default "consistent")

This rule is triggered when different heading styles (atx, setext, and 'closed'
atx) are used in the same document:

# ATX style H1

## Closed ATX style H2 ##

Setext style H1
===============

Be consistent with the style of heading used in a document:

# ATX style H1

## ATX style H2

The setext_with_atx and setext_with_atx_closed doc styles allow atx-style
headings of level 3 or more in documents with setext style headings:

Setext style H1
===============

Setext style H2
---------------

### ATX style H3

Note: the configured heading style can be a specific style to use (atx,
atx_closed, setext, setext_with_atx, setext_with_atx_closed), or simply require
that the usage be consistent within the document.

Rationale: Consistent formatting makes it easier to understand a document.

## MD004 - Unordered list style

Tags: bullet, ul

Aliases: ul-style

Parameters: style ("consistent", "asterisk", "plus", "dash", "sublist"; default
"consistent")

This rule is triggered when the symbols used in the document for unordered
list items do not match the configured unordered list style:

* Item 1
+ Item 2
- Item 3

To fix this issue, use the configured style for list items throughout the
document:

* Item 1
* Item 2
* Item 3

The configured list style can be a specific symbol to use (asterisk, plus, dash),
can require that usage be consistent within the document, or can require that each
sublist have a consistent symbol that is different from its parent list.

For example, the following is valid for the sublist style because the outer-most
indent uses asterisk, the middle indent uses plus, and the inner-most indent uses dash:

* Item 1
+ Item 2
- Item 3
+ Item 4
* Item 4
+ Item 5

Rationale: Consistent formatting makes it easier to understand a document.

## MD005 - Inconsistent indentation for list items at the same level

Tags: bullet, ul, indentation

Aliases: list-indent

Fixable: Most violations can be fixed by tooling

This rule is triggered when list items are parsed as being at the same level,
but don't have the same indentation:

* Item 1
* Nested Item 1
* Nested Item 2
* A misaligned item

Usually this rule will be triggered because of a typo. Correct the indentation
for the list to fix it:

* Item 1
* Nested Item 1
* Nested Item 2
* Nested Item 3

Sequentially-ordered list markers are usually left-aligned such that all items
have the same starting column:

...
8. Item
9. Item
10. Item
11. Item
...

This rule also supports right-alignment of list markers such that all items have
the same ending column:

...
8. Item
9. Item
10. Item
11. Item
...

Rationale: Violations of this rule can lead to improperly rendered content.

## MD006 - Consider starting bulleted lists at the beginning of the line

Tags: bullet, ul, indentation

Aliases: ul-start-left

Fixable: Most violations can be fixed by tooling

This rule is triggered when top level lists don't start at the beginning of a
line:

Some text

* List item
* List item

To fix, ensure that top level list items are not indented:

Some test

* List item
* List item

Note: This rule is triggered for the following scenario because the unordered
sublist is not recognized as such by the parser. Not being nested 3 characters
as required by the outer ordered list, it creates a top-level unordered list

1. List item
- List item
- List item
1. List item

Rationale: Starting lists at the beginning of the line means that nested list
items can all be indented by the same amount when an editor's indent function
or the tab key is used to indent. Starting a list 1 space in means that the
indent of the first nested list is less than the indent of the second level (3
characters if you use 4 space tabs, or 1 character if you use 2 space tabs).

## MD007 - Unordered list indentation

Tags: bullet, ul, indentation

Aliases: ul-indent

Parameters: indent, start_indented (number; default 2, boolean; default false)

Fixable: Most violations can be fixed by tooling

This rule is triggered when list items are not indented by the configured
number of spaces (default: 2).

Example:

* List item
* Nested list item indented by 3 spaces

Corrected Example:

* List item
* Nested list item indented by 2 spaces

Note: This rule applies to a sublist only if its parent lists are all also
unordered (otherwise, extra indentation of ordered lists interferes with the
rule).

The start_indented parameter allows the first level of lists to be indented by
the configured number of spaces rather than starting at zero (the inverse of
MD006).

Rationale: Indenting by 2 spaces allows the content of a nested list to be in
line with the start of the content of the parent list when a single space is
used after the list marker. Indenting by 4 spaces is consistent with code blocks
and simpler for editors to implement. Additionally, this can be a compatibility
https://cirosantilli.com/markdown-style-guide#indentation-of-content-inside-lists
and http://support.markedapp.com/discussions/problems/21-sub-lists-not-indenting.

## MD009 - Trailing spaces

Tags: whitespace

Aliases: no-trailing-spaces

Parameters: br_spaces, list_item_empty_lines, strict (number; default 2, boolean; default false, boolean; default false)

Fixable: Most violations can be fixed by tooling

This rule is triggered on any lines that end with unexpected whitespace. To fix this,
remove the trailing space from the end of the line.

The br_spaces parameter allows an exception to this rule for a specific number
of trailing spaces, typically used to insert an explicit line break. The default
value allows 2 spaces to indicate a hard break (\
element).

Note: You must set br_spaces to a value >= 2 for this parameter to take effect.
Setting br_spaces to 1 behaves the same as 0, disallowing any trailing spaces.

By default, this rule will not trigger when the allowed number of spaces is used,
even when it doesn't create a hard break (for example, at the end of a paragraph).
To report such instances as well, set the strict parameter to true.

Text text text
text[2 spaces]

Using spaces to indent blank lines inside a list item is usually not necessary,
but some parsers require it. Set the list_item_empty_lines parameter to true
to allow this (even when strict is true):

- list item text
[2 spaces]
list item text

Rationale: Except when being used to create a line break, trailing whitespace
has no purpose and does not affect the rendering of content.

## MD010 - Hard tabs

Tags: whitespace, hard_tab

Aliases: no-hard-tabs

Parameters: code_blocks (boolean; default true)

Fixable: Most violations can be fixed by tooling

This rule is triggered by any lines that contain hard tab characters instead
of using spaces for indentation. To fix this, replace any hard tab characters

Example:

Some text

* hard tab character used to indent the list item

Corrected example:

Some text

* Spaces used to indent the list item instead

You have the option to exclude this rule for code blocks. To do so, set the
code_blocks parameter to false. Code blocks are included by default since
handling of tabs by tools is often inconsistent (ex: using 4 vs. 8 spaces).

Rationale: Hard tabs are often rendered inconsistently by different editors and
can be harder to work with than spaces.

## MD011 - Reversed link syntax

Fixable: Most violations can be fixed by tooling

This rule is triggered when text that appears to be a link is encountered, but
where the syntax appears to have been reversed (the [] and () are
reversed):

(Incorrect link syntax)[https://www.example.com/]

To fix this, swap the [] and () around:

[Correct link syntax](https://www.example.com/)

Note: Markdown Extra-style footnotes do not trigger this rule:

For (example)[^1]

## MD012 - Multiple consecutive blank lines

Tags: whitespace, blank_lines

Aliases: no-multiple-blanks

Parameters: maximum (number; default 1)

Fixable: Most violations can be fixed by tooling

This rule is triggered when there are multiple consecutive blank lines in the
document:

Some text here

Some more text here

To fix this, delete the offending lines:

Some text here

Some more text here

Note: this rule will not be triggered if there are multiple consecutive blank
lines inside code blocks.

Note: The maximum parameter can be used to configure the maximum number of
consecutive blank lines.

Rationale: Except in a code block, blank lines serve no purpose and do not
affect the rendering of content.

## MD013 - Line length

Tags: line_length

Aliases: line-length

Parameters: line_length, heading_line_length, code_block_line_length, code_blocks, tables, headings, headers, strict, stern (number; default 80 for *_length, boolean; default true (except strict/stern which default false))

If headings is not provided, headers (deprecated) will be used.

This rule is triggered when there are lines that are longer than the
configured line_length (default: 80 characters). To fix this, split the line
up into multiple lines. To set a different maximum length for headings, use
heading_line_length. To set a different maximum length for code blocks, use
code_block_line_length

This rule has an exception when there is no whitespace beyond the configured
line length. This allows you to still include items such as long URLs without
being forced to break them in the middle. To disable this exception, set the
strict parameter to true to report an issue when any line is too long.
To warn for lines that are too long and could be fixed but allow lines without
spaces, set the stern parameter to true.

For example (assuming normal behavior):

IF THIS LINE IS THE MAXIMUM LENGTH
This line is okay because there are-no-spaces-beyond-that-length
And this line is a violation because there are
This-line-is-also-okay-because-there-are-no-spaces

In strict or stern modes, the two middle lines above are a violation. The
third line is a violation in strict mode, but allowed in stern mode.

You have the option to exclude this rule for code blocks, tables, or headings.
To do so, set the code_blocks, tables, or headings parameter(s) to false.

Code blocks are included in this rule by default since it is often a
requirement for document readability, and tentatively compatible with code
rules. Still, some languages do not lend themselves to short lines.

Rationale: Extremely long lines can be difficult to work with in some editors.

## MD014 - Dollar signs used before commands without showing output

Tags: code

Aliases: commands-show-output

Fixable: Most violations can be fixed by tooling

This rule is triggered when there are code blocks showing shell commands to be
typed, and all of the shell commands are preceded by dollar signs ($): $ ls
$cat foo$ less bar

The dollar signs are unnecessary in this situation, and should not be
included:

ls
cat foo
less bar

Showing output for commands preceded by dollar signs does not trigger this rule:

$ls foo bar$ cat foo
Hello world
$cat bar baz Because some commands do not produce output, it is not a violation if some commands do not have output: $ mkdir test
mkdir: created directory 'test'
\$ ls test

Rationale: It is easier to copy/paste and less noisy if the dollar signs
are omitted when they are not needed. See
https://cirosantilli.com/markdown-style-guide#dollar-signs-in-shell-code

## MD018 - No space after hash on atx style heading

Aliases: no-missing-space-atx

Fixable: Most violations can be fixed by tooling

This rule is triggered when spaces are missing after the hash characters

#Heading 1

##Heading 2

To fix this, separate the heading text from the hash character by a single
space:

# Heading 1

## Heading 2

Rationale: Violations of this rule can lead to improperly rendered content.

## MD019 - Multiple spaces after hash on atx style heading

Aliases: no-multiple-space-atx

Fixable: Most violations can be fixed by tooling

This rule is triggered when more than one space is used to separate the

#  Heading 1

##  Heading 2

To fix this, separate the heading text from the hash character by a single
space:

# Heading 1

## Heading 2

Rationale: Extra space has no purpose and does not affect the rendering of
content.

## MD020 - No space inside hashes on closed atx style heading

Aliases: no-missing-space-closed-atx

Fixable: Most violations can be fixed by tooling

This rule is triggered when spaces are missing inside the hash characters
in a closed atx style heading:

#Heading 1#

##Heading 2##

To fix this, separate the heading text from the hash character by a single
space:

# Heading 1 #

## Heading 2 ##

Note: this rule will fire if either side of the heading is missing spaces.

Rationale: Violations of this rule can lead to improperly rendered content.

## MD021 - Multiple spaces inside hashes on closed atx style heading

Aliases: no-multiple-space-closed-atx

Fixable: Most violations can be fixed by tooling

This rule is triggered when more than one space is used to separate the
heading text from the hash characters in a closed atx style heading:

#  Heading 1  #

##  Heading 2  ##

To fix this, separate the heading text from the hash character by a single
space:

# Heading 1 #

## Heading 2 ##

Note: this rule will fire if either side of the heading contains multiple
spaces.

Rationale: Extra space has no purpose and does not affect the rendering of
content.

## MD022 - Headings should be surrounded by blank lines

Parameters: lines_above, lines_below (number; default 1)

Fixable: Most violations can be fixed by tooling

This rule is triggered when headings (any style) are either not preceded or not
followed by at least one blank line:

# Heading 1
Some text

Some more text
## Heading 2

To fix this, ensure that all headings have a blank line both before and after
(except where the heading is at the beginning or end of the document):

# Heading 1

Some text

Some more text

## Heading 2

The lines_above and lines_below parameters can be used to specify a different
number of blank lines (including 0) above or below each heading.

Note: If lines_above or lines_below are configured to require more than one
blank line, MD012/no-multiple-blanks should also be customized.

Rationale: Aside from aesthetic reasons, some parsers, including kramdown, will
not parse headings that don't have a blank line before, and will parse them as
regular text.

## MD023 - Headings must start at the beginning of the line

Fixable: Most violations can be fixed by tooling

This rule is triggered when a heading is indented by one or more spaces:

Some text

# Indented heading

To fix this, ensure that all headings start at the beginning of the line:

Some text

# Heading

Rationale: Headings that don't start at the beginning of the line will not be

## MD024 - Multiple headings with the same content

Parameters: siblings_only, allow_different_nesting (boolean; default false)

This rule is triggered if there are multiple headings in the document that have
the same text:

# Some text

## Some text

To fix this, ensure that the content of each heading is different:

# Some text

## Some more text

If the parameter siblings_only (alternatively allow_different_nesting) is
set to true, heading duplication is allowed for non-sibling headings (common
in change logs):

# Change log

## 1.0.0

### Features

## 2.0.0

### Features

Rationale: Some markdown parsers generate anchors for headings based on the
heading name; headings with the same content can cause problems with that.

## MD025 - Multiple top level headings in the same document

Aliases: single-title, single-h1

Parameters: level, front_matter_title (number; default 1, string; default "^\s*title:")

This rule is triggered when a top level heading is in use (the first line of
the file is an h1 heading), and more than one h1 heading is in use in the
document:

# Top level heading

# Another top level heading

To fix, structure your document so that there is a single h1 heading that is
the title for the document, and all later headings are h2 or lower level

# Title

## Another heading

Note: The level parameter can be used to change the top level (ex: to h2) in
cases where an h1 is added externally.

If YAML front matter is present and contains
a title property (commonly used with blog posts), this rule treats that as a top
level heading and will report a violation for any subsequent top level headings.
To use a different property name in front matter, specify the text of a regular
expression via the front_matter_title parameter. To disable the use of front
matter by this rule, specify "" for front_matter_title.

Rationale: A top level heading is an h1 on the first line of the file, and
serves as the title for the document. If this convention is in use, then there
can not be more than one title for the document, and the entire document
should be contained within this heading.

## MD026 - Trailing punctuation in heading

Aliases: no-trailing-punctuation

Parameters: punctuation (string; default ".,;:!?。，；：！？")

Fixable: Most violations can be fixed by tooling

This rule is triggered on any heading that has one of the specified normal or
full-width punctuation characters as the last character in the line:

# This is a heading.

To fix this, remove the trailing punctuation:

# This is a heading

Note: The punctuation parameter can be used to specify what characters count
as punctuation at the end of a heading. For example, you can change it to
".,;:!" to allow headings that end with a question mark, such as in an FAQ.
Setting the punctuation parameter to "" allows all characters - and is
equivalent to disabling the rule.

## MD027 - Multiple spaces after blockquote symbol

Tags: blockquote, whitespace, indentation

Aliases: no-multiple-space-blockquote

Fixable: Most violations can be fixed by tooling

This rule is triggered when blockquotes have more than one space after the
blockquote (>) symbol:

>  This is a block quote with bad indentation
>  there should only be one.

To fix, remove any extraneous space:

> This is a blockquote with correct
> indentation.

Rationale: Consistent formatting makes it easier to understand a document.

## MD028 - Blank line inside blockquote

Tags: blockquote, whitespace

Aliases: no-blanks-blockquote

Fixable: Most violations can be fixed by tooling

This rule is triggered when two blockquote blocks are separated by nothing
except for a blank line:

> This is a blockquote
> which is immediately followed by

> this blockquote. Unfortunately
> In some parsers, these are treated as the same blockquote.

To fix this, ensure that any blockquotes that are right next to each other
have some text in between:

> This is a blockquote.

And Jimmy also said:

> This too is a blockquote.

Alternatively, if they are supposed to be the same quote, then add the
blockquote symbol at the beginning of the blank line:

> This is a blockquote.
>
> This is the same blockquote.

Rationale: Some markdown parsers will treat two blockquotes separated by one
or more blank lines as the same blockquote, while others will treat them as
separate blockquotes.

## MD029 - Ordered list item prefix

Tags: ol

Aliases: ol-prefix

Parameters: style ("one", "ordered", "one_or_ordered", "zero"; default "one_or_ordered")

This rule is triggered for ordered lists that do not either start with '1.' or
do not have a prefix that increases in numerical order (depending on the
configured style). The less-common patterns of using '0.' as a first prefix or
for all prefixes is also supported.

Example valid list if the style is configured as 'one':

1. Do this.
1. Do that.
1. Done.

Examples of valid lists if the style is configured as 'ordered':

1. Do this.
2. Do that.
3. Done.
0. Do this.
1. Do that.
2. Done.

All three examples are valid when the style is configured as 'one_or_ordered'.

Example valid list if the style is configured as 'zero':

0. Do this.
0. Do that.
0. Done.

Example invalid list for all styles:

1. Do this.
3. Done.

This rule supports 0-prefixing ordered list items for uniform indentation:

...
08. Item
09. Item
10. Item
11. Item
...

Note: This rule will report violations for cases like the following where an improperly-indented code block (or similar) appears between two list items and "breaks" the list in two:

1. First list

text
Code block


1. Second list

The fix is to indent the code block so it becomes part of the preceding list item as intended:

1. First list

text
Code block


2. Still first list

Rationale: Consistent formatting makes it easier to understand a document.

## MD030 - Spaces after list markers

Tags: ol, ul, whitespace

Aliases: list-marker-space

Parameters: ul_single, ol_single, ul_multi, ol_multi (number; default 1)

Fixable: Most violations can be fixed by tooling

This rule checks for the number of spaces between a list marker (e.g. '-',
'*', '+' or '1.') and the text of the list item.

The number of spaces checked for depends on the document style in use, but the
default is 1 space after any list marker:

* Foo
* Bar
* Baz

1. Foo
1. Bar
1. Baz

1. Foo
* Bar
1. Baz

A document style may change the number of spaces after unordered list items
and ordered list items independently, as well as based on whether the content
of every item in the list consists of a single paragraph, or multiple
paragraphs (including sub-lists and code blocks).

For example, the style guide at
https://cirosantilli.com/markdown-style-guide#spaces-after-list-marker
specifies that 1 space after the list marker should be used if every item in
the list fits within a single paragraph, but to use 2 or 3 spaces (for ordered
and unordered lists respectively) if there are multiple paragraphs of content
inside the list:

* Foo
* Bar
* Baz

vs.

*   Foo

Second paragraph

*   Bar

or

1.  Foo

Second paragraph

1.  Bar

To fix this, ensure the correct number of spaces are used after list marker

Rationale: Violations of this rule can lead to improperly rendered content.

## MD031 - Fenced code blocks should be surrounded by blank lines

Tags: code, blank_lines

Aliases: blanks-around-fences

Parameters: list_items (boolean; default true)

Fixable: Most violations can be fixed by tooling

This rule is triggered when fenced code blocks are either not preceded or not
followed by a blank line:

Some text

Code block

Another code block

Some more text

To fix this, ensure that all fenced code blocks have a blank line both before
and after (except where the block is at the beginning or end of the document):

Some text


Code block

Another code block


Some more text

Set the list_items parameter to false to disable this rule for list items.
Disabling this behavior for lists can be useful if it is necessary to create a
tight list containing a code fence.

Rationale: Aside from aesthetic reasons, some parsers, including kramdown, will
not parse fenced code blocks that don't have blank lines before and after them.

## MD032 - Lists should be surrounded by blank lines

Tags: bullet, ul, ol, blank_lines

Aliases: blanks-around-lists

Fixable: Most violations can be fixed by tooling

This rule is triggered when lists (of any kind) are either not preceded or not
followed by a blank line:

Some text
* Some
* List

1. Some
2. List
Some text

To fix this, ensure that all lists have a blank line both before and after
(except where the block is at the beginning or end of the document):

Some text

* Some
* List

1. Some
2. List

Some text

Rationale: Aside from aesthetic reasons, some parsers, including kramdown, will
not parse lists that don't have blank lines before and after them.

## MD033 - Inline HTML

Tags: html

Aliases: no-inline-html

Parameters: allowed_elements (array of string; default empty)

This rule is triggered whenever raw HTML is used in a markdown document:

<h1>Inline HTML heading</h1>

To fix this, use 'pure' markdown instead of including raw HTML:

# Markdown heading

Note: To allow specific HTML elements, use the 'allowed_elements' parameter.

Rationale: Raw HTML is allowed in markdown, but this rule is included for
those who want their documents to only include "pure" markdown, or for those
who are rendering markdown documents in something other than HTML.

## MD034 - Bare URL used

Aliases: no-bare-urls

Fixable: Most violations can be fixed by tooling

This rule is triggered whenever a URL is given that isn't surrounded by angle
brackets:

For more information, see https://www.example.com/.

To fix this, add angle brackets around the URL:

For more information, see <https://www.example.com/>.

Note: To use a bare URL without it being converted into a link, enclose it in
a code block, otherwise in some markdown parsers it will be converted:

https://www.example.com

Note: The following scenario does not trigger this rule to avoid conflicts
with MD011/no-reversed-links:

[https://www.example.com]

The use of quotes around a bare link will not trigger this rule, either:

"https://www.example.com"
'https://www.example.com'

Rationale: Without angle brackets, the URL isn't converted into a link by many
markdown parsers.

## MD035 - Horizontal rule style

Tags: hr

Aliases: hr-style

Parameters: style ("consistent", "---", "***", or other string specifying the
horizontal rule; default "consistent")

This rule is triggered when inconsistent styles of horizontal rules are used
in the document:

---

- - -

***

* * *

****

To fix this, ensure any horizontal rules used in the document are consistent,
or match the given style if the rule is so configured:

---

---

Note: by default, this rule is configured to just require that all horizontal
rules in the document are the same, and will trigger if any of the horizontal
rules are different than the first one encountered in the document. If you
want to configure the rule to match a specific style, the parameter given to
the 'style' option is a string containing the exact horizontal rule text that
is allowed.

Rationale: Consistent formatting makes it easier to understand a document.

Parameters: punctuation (string; default ".,;:!?。，；：！？")

This check looks for instances where emphasized (i.e. bold or italic) text is

**My document**

Lorem ipsum dolor sit amet...

_Another section_

Consectetur adipiscing elit, sed do eiusmod.

To fix this, use markdown headings instead of emphasized text to denote
sections:

# My document

Lorem ipsum dolor sit amet...

## Another section

Consectetur adipiscing elit, sed do eiusmod.

Note: This rule looks for single line paragraphs that consist entirely
of emphasized text. It won't fire on emphasis used within regular text,
multi-line emphasized paragraphs, or paragraphs ending in punctuation
(normal or full-width). Similarly to rule MD026, you can configure what
characters are recognized as punctuation.

## MD037 - Spaces inside emphasis markers

Tags: whitespace, emphasis

Aliases: no-space-in-emphasis

Fixable: Most violations can be fixed by tooling

This rule is triggered when emphasis markers (bold, italic) are used, but they
have spaces between the markers and the text:

Here is some ** bold ** text.

Here is some * italic * text.

Here is some more __ bold __ text.

Here is some more _ italic _ text.

To fix this, remove the spaces around the emphasis markers:

Here is some **bold** text.

Here is some *italic* text.

Here is some more __bold__ text.

Here is some more _italic_ text.

Rationale: Emphasis is only parsed as such when the asterisks/underscores
aren't completely surrounded by spaces. This rule attempts to detect where
they were surrounded by spaces, but it appears that emphasized text was
intended by the author.

## MD038 - Spaces inside code span elements

Tags: whitespace, code

Aliases: no-space-in-code

Fixable: Most violations can be fixed by tooling

This rule is triggered for code span elements that have spaces adjacent to the
backticks:

some text

 some text

To fix this, remove any spaces adjacent to the backticks:

some text

Note: A single leading and trailing space is allowed by the specification and
automatically trimmed (to allow for embedded backticks):

 backticks 

Note: A single leading or trailing space is allowed if used to separate codespan
markers from an embedded backtick:

  embedded backtick

Rationale: Violations of this rule can lead to improperly rendered content.

## MD039 - Spaces inside link text

Fixable: Most violations can be fixed by tooling

This rule is triggered on links that have spaces surrounding the link text:

[ a link ](https://www.example.com/)

To fix this, remove the spaces surrounding the link text:

[a link](https://www.example.com/)

Rationale: Consistent formatting makes it easier to understand a document.

## MD040 - Fenced code blocks should have a language specified

Tags: code, language

Aliases: fenced-code-language

This rule is triggered when fenced code blocks are used, but a language isn't
specified:

# !/bin/bash

echo Hello world

To fix this, add a language specifier to the code block:

​bash
#!/bin/bash
echo Hello world

Rationale: Specifying a language improves content rendering by using the
<https://cirosantilli.com/markdown-style-guide#option-code-fenced>.

<a name="md041"></a>

## MD041 - First line in file should be a top level heading

Parameters: level, front_matter_title (number; default 1, string; default "^\s*title:")

This rule is intended to ensure documents have a title and is triggered when
the first line in the file isn't a top level (h1) heading:

​markdown
This is a file without a heading

To fix this, add a top level heading to the beginning of the file:

# File with heading

This is a file with a top level heading

Note: The level parameter can be used to change the top level (ex: to h2) in cases
where an h1 is added externally.

If YAML front matter is present and contains a
title property (commonly used with blog posts), this rule will not report a
violation. To use a different property name in front matter, specify the text
of a regular expression via the front_matter_title parameter. To disable the
use of front matter by this rule, specify "" for front_matter_title.

Rationale: The top level heading often acts as the title of a document. More

## MD042 - No empty links

This rule is triggered when an empty link is encountered:

[an empty link]()

To fix the violation, provide a destination for the link:

[a valid link](https://example.com/)

Empty fragments will trigger this rule:

[an empty fragment](#)

But non-empty fragments will not:

[a valid fragment](#fragment)

## MD043 - Required heading structure

Parameters: headings, headers (array of string; default null for disabled)

If headings is not provided, headers (deprecated) will be used.

This rule is triggered when the headings in a file do not match the array of
headings passed to the rule. It can be used to enforce a standard heading
structure for a set of files.

To require exactly the following structure:

# Head
## Item
### Detail

Set the headings parameter to:

[
"## Item",
"### Detail"
]

To allow optional headings as with the following structure:

# Head
## Item
### Detail (optional)
## Foot
### Notes (optional)

Use the special value "*" meaning "one or more unspecified headings" and set
the headings parameter to:

[
"## Item",
"*",
"## Foot",
"*"
]

When an error is detected, this rule outputs the line number of the first
problematic heading (otherwise, it outputs the last line number of the file).

Note that while the headings parameter uses the "## Text" ATX heading style for
simplicity, a file may use any supported heading style.

Rationale: Projects may wish to enforce a consistent document structure across
a set of similar content.

## MD044 - Proper names should have the correct capitalization

Tags: spelling

Aliases: proper-names

Parameters: names, code_blocks (string array; default null, boolean; default true)

Fixable: Most violations can be fixed by tooling

This rule is triggered when any of the strings in the names array do not have
the specified capitalization. It can be used to enforce a standard letter case
for the names of projects and products.

For example, the language "JavaScript" is usually written with both the 'J' and
'S' capitalized - though sometimes the 's' or 'j' appear in lower-case. To enforce
the proper capitalization, specify the desired letter case in the names array:

[
"JavaScript"
]

Set the code_blocks parameter to false to disable this rule for code blocks.

Rationale: Incorrect capitalization of proper names is usually a mistake.

## MD045 - Images should have alternate text (alt text)

Tags: accessibility, images

Aliases: no-alt-text

This rule is triggered when an image is missing alternate text (alt text) information.

Alternate text is commonly specified inline as:

![Alternate text](image.jpg)

Or with reference syntax as:

![Alternate text][ref]

...

[ref]: image.jpg "Optional title"

Guidance for writing alternate text is available from the W3C,
Wikipedia, and
other locations.

Rationale: Alternate text is important for accessibility and describes the
content of an image for people who may not be able to see it.

## MD046 - Code block style

Tags: code

Aliases: code-block-style

Parameters: style ("consistent", "fenced", "indented"; default "consistent")

This rule is triggered when unwanted or different code block styles are used in
the same document.

In the default configuration this rule reports a violation for the following document:

Some text.

# Indented code

More text.

ruby
# Fenced code


More text.

To fix violations of this rule, use a consistent style (either indenting or code fences).

The specified style can be specific (fenced, indented) or simply require that usage
be consistent within the document (consistent).

Rationale: Consistent formatting makes it easier to understand a document.

## MD047 - Files should end with a single newline character

Tags: blank_lines

Aliases: single-trailing-newline

Fixable: Most violations can be fixed by tooling

This rule is triggered when there is not a single newline character at the end of a file.

Example that triggers the rule:

# Heading

This file ends without a newline.[EOF]

To fix the violation, add a newline character to the end of the file:

# Heading

This file ends with a newline.
[EOF]

Rationale: Some programs have trouble with files that do not end with a newline.

## MD048 - Code fence style

Tags: code

Aliases: code-fence-style

Parameters: style ("consistent", "tilde", "backtick"; default "consistent")

This rule is triggered when the symbols used in the document for fenced code blocks do not match the configured code fence style:

​ruby
# Fenced code
# Fenced code

To fix this issue, use the configured code fence style throughout the
document:

​markdown
​ruby
# Fenced code
# Fenced code

The configured list style can be a specific symbol to use (backtick, tilde), or
can require that usage be consistent within the document.

Rationale: Consistent formatting makes it easier to understand a document.
`
Last modification：July 12, 2020