Documentation/markdown.md - gitiles - Rivoreo Source Code Repositories

 # Markdown

 The [Gitiles](https://code.google.com/p/gitiles/) source browser
 automatically renders `*.md` Markdown files into HTML for simplified
 documentation.

 [TOC]

 ## Access controls

 Access controls for documentation is identical to source code.

 Documentation stored with source files shares the same permissions.
 Documentation stored in a separate Git repository can use different
 access controls.  If Gerrit Code Review is being used, branch level
 read permissions can be used to grant or restrict access to any
 documentation branches.

 ## READMEs

 Files named `README.md` are automatically displayed below the file's
 directory listing.  For the top level directory this mirrors the
 standard [GitHub](https://github.com/) presentation.

 *** promo
 README.md files are meant to provide orientation for developers
 browsing the repository, especially first-time users.
 ***

 We recommend that Git repositories have an up-to-date top-level
 `README.md` file.

 ## Markdown syntax

 Gitiles supports the core Markdown syntax described in
 [Markdown Basics]. Additional extensions are supported
 to more closely match [GitHub Flavored Markdown] and
 simplify documentation writing.

 [Markdown Basics]: http://daringfireball.net/projects/markdown/basics
 [GitHub Flavored Markdown]: https://help.github.com/articles/github-flavored-markdown/

 ### Paragraphs

 Paragraphs are one or more lines of consecutive text, followed by
 one or more blank lines. Line breaks within a paragraph are ignored
 by the parser, allowing authors to line-wrap text at any comfortable
 column width.

 ```
 Documentation writing can be fun and profitable
 by helping users to learn and solve problems.

 After documentation is written, it needs to be published on the
 web where it can be easily accessed for reading.
 ```

 ### Headings

 Headings can be indicated by starting the line with one or more `#`
 marks.  The number of `#` used determines the depth of the heading in
 the document outline.  Headings 1 through 6 (`######`) are supported.

 ```
 # A level one (H1) heading
 ## A level two (H2) heading
 ### A level three (H3) heading
 ```

 Headings can also use the less popular two line `======` and `------`
 forms to create H1 and H2 level headers:

 ```
 A first level header
 ====================

 A second level header
 ---------------------
 ```

 This form is discouraged as maintaining the length of the `===` or
 `---` lines to match the preceding line can be tedious work that is
 unnecessary with the `#` headers.

 ### Lists

 A bullet list:

 ```
 * Fruit
     * Orange
     * Pear
 * Cake
 ```

 will render into HTML as:

 * Fruit
     * Orange
     * Pear
 * Cake

 The second level items (above Orange, Pear) must be indented with more
 spaces than the item they are nested under. Above 2 spaces were used.
 Additionally, the entire list must be preceded and followed by a blank
 line.

 A numbered list:

 ```
 1. Fruit
      1. Orange
      2. Pear
 5. Cake
 ```

 will render into HTML as:

 1. Fruit
      1. Orange
      2. Pear
 5. Cake

 List items will be renumbered sequentially by the browser, which is
 why `5` above displays as `2`. Even with this feature it is a good
 idea to maintain list item numbers in the source Markdown to simplify
 reading the source file.

 Like bullet lists, numbered lists can be nested by using more leading
 space than the prior list item.

 ### Tables

 Simple tables are supported with column alignment.  The first line is
 the header row and subsequent lines are data rows:

 ```
 | Food  | Calories | Tasty? |
 |-------|---------:|:------:|
 | Apple |    95    | Yes    |
 | Pear  |   102    | Yes    |
 | Hay   |   977    |        |
 ```

 will render as:

 | Food  | Calories | Tasty? |
 |-------|---------:|:------:|
 | Apple |    95    | Yes    |
 | Pear  |   102    | Yes    |
 | Hay   |   977    |        |

 Placing `:` in the separator line indicates how the column should be
 aligned.  A colon on the left side is a **left-aligned** column; a
 colon on the right-most side is **right-aligned**; a colon on both
 sides is **center-aligned**.

 Empty table cells are indicated by whitespace between the column
 dividers (`| |`) while multiple column cells omit the whitespace.

 ### Emphasis

 Emphasize paragraph text with *italic* and **bold** styles.  Either `_`
 or `*` can be used for italic (1 character) and bold text (2
 characters).  This allows styles to be mixed within a statement:

 ```
 Emphasize paragraph text with *italic* and **bold** text.

 **It is _strongly_ encouraged to review documentation for typos.**
 ```

 **It is _strongly_ encouraged to review documentation for typos.**

 Emphasis within_words_is_ignored which helps write technical
 documentation. Literal \*bold* can be forced by prefixing the
 opening `*` with \ such as `\*bold*`.

 ### Strikethrough

 Text can be ~~struck out~~ within a paragraph:

 ```
 Text can be ~~struck out~~ within a paragraph.
 ```

 Note two tildes are required (`~~`) on either side of the struck out
 section of text.

 ### Blockquotes

 Blockquoted text can be used to stand off text obtained from
 another source:

 ```
 Sir Winston Churchill once said:

 > A lie gets halfway around the world before the truth has a
 > chance to get its pants on.
 ```

 renders as:

 Sir Winston Churchill once said:

 > A lie gets halfway around the world before the truth has a
 > chance to get its pants on.

 ### Code (inline)

 Use `backticks` to markup inline code within a paragraph:

 ```
 Use `backticks` to markup inline code within a paragraph.
 ```

 ### Code (blocks)

 Create a fenced code block using three backticks before and after a
 block of code, preceeded and followed by blank lines:

 ````
 This is a simple hello world program in C:

 ``` c
 #include <stdio.h>

 int main() {
   printf("Hello, World.\n");
   return 0;
 }
 ```

 To compile it use `gcc hello.c`.
 ````

 Text within a fenced code block is taken verbatim and is not
 processed for Markdown markup.

 Syntax highlighting can optionally be enabled for common languages
 by adding the language name in lowercase on the opening line.
 Supported languages include:

 |||---||| 2,2,2,2,4

 #### Scripting
 * bash, sh
 * lua
 * perl
 * python, py
 * ruby
 * tcl

 #### Web
 * css
 * dart
 * html
 * javascript, js
 * json

 #### Compiled
 * basic, vb
 * c
 * cpp (C++)
 * go
 * java
 * pascal
 * scala

 #### Markup
 * tex, latex
 * wiki
 * xml
 * xquery
 * xsl
 * yaml

 #### Other
 * clj (Clojure)
 * erlang
 * hs (Haskell)
 * lisp
 * [llvm](http://llvm.org/docs/LangRef.html)
 * matlab
 * ml (OCaml, SML, F#)
 * r
 * [rd](http://cran.r-project.org/doc/manuals/R-exts.html)
 * rust
 * sql
 * vhdl
 |||---|||

 ### Horizontal rules

 A horizontal rule can be inserted using GitHub style `--` surrounded
 by blank lines.  Alternatively repeating `-` or `*` and space on a
 line will also create a horizontal rule:

 ```
 ---

 - - - -

 * * * *
 ```

 ### Links

 Wrap text in `[brackets]` and the link destination in parens
 `(http://...)` such as:

 ```
 Visit [this site](http://example.com/) for more examples.
 ```

 Links can also use references to obtain URLs from elsewhere in the
 same document.  This style can be useful if the same URL needs to be
 mentioned multiple times, is too long to cleanly place within text,
 or the link is within a table cell:

 ```
 Search for [markdown style][1] examples.

 [1]: https://www.google.com/?gws_rd=ssl#q=markdown+style+guide
 ```

 References can be simplified if the text alone is sufficient:

 ```
 Visit [Google] to search the web.

 [Google]: https://www.google.com/
 ```

 Automatic hyperlinking can be used where the link text should
 obviously also be the URL:

 ```
 Use https://www.google.com/ to search the web.
 ```

 Well formed URLs beginning with `https://`, `http://`, and `mailto:`
 are used as written for the link's destination.  Malformed URLs may be
 replaced with `#zSoyz` to prevent browser evaluation of dangerous
 content.

 HTML escaping of URL characters such as `&` is handled internally by
 the parser/formatter.  Documentation writers should insert the URL
 literally and allow the parser and formatter to make it HTML safe.

 Relative links such as `../src/api.md` are resolved relative to the
 current markdown's file path within the Git repository.  Absolute
 links such as `/src/api.md` are resolved relative to the top of the
 enclosing Git repository, but within the same branch or Git commit.
 Links may point to any file in the repository.  A link to a `*.md`
 file will present the rendered markdown, while a link to a source file
 will display the syntax highlighted source.

 ### Named anchors

 Explicit anchors can be inserted anywhere in the document using
 `<a name="tag"></a>` or `{#tag}`.

 Implicit anchors are automatically created for each
 [heading](#Headings).  For example `## Section 1` will have
 the anchor `Section-1`.

 *** note
 *Anchor generation*

 * letters and digits, after removing accents (á →  a)
 * spaces are replaced with hyphens (`-`)
 * other characters are replaced with underscores (`_`)
 * runs of hyphens and underscores are collapsed
 ***

 If a document contains the same named subsection under different
 parents the parent anchor will prefix the subsections to
 disambiguate. For example the following document will have anchors
 `Running-Format` and `Coding-Format` and `Libraries` as that subsection
 is unique:

 ```
 ## Running
 ### Format
 ## Coding
 ### Format
 ### Libraries
 ```

 When placed in a section header the explicit anchor will override
 the automatic anchor.  The following are identical and associate
 the anchor `live-examples` with the section header instead of the
 automaticly generated name `Examples`.

 ```
 ## Examples {#live-examples}
 ## Examples <a name="live-examples"></a>
 ```

 ### Images

 Similar to links but begin with `!` to denote an image reference:

 ```
 ![diffy the kung fu review cuckoo](http://commondatastorage.googleapis.com/gerrit-static/diffy-w200.png)
 ```

 For images the text in brackets will be included as the alt text for
 screen readers.

 Well formed image URLs beginning with `https://` and `http://` will be
 used as written for the `<img src="...">` attribute.  Malformed URLs
 will be replaced with a broken `data:` reference to prevent browsers
 from trying to load a bad destination.

 Relative and absolute links to image files within the Git repository
 (such as `../images/banner.png`) are resolved during rendering by
 inserting the base64 encoding of the image using a `data:` URI.  Only
 PNG (`*.png`), JPEG (`*.jpg` or `*.jpeg`) and GIF (`*.gif`) image
 formats are supported when referenced from the Git repository.

 Unsupported extensions or files larger than [image size](#Image-size)
 limit (default 256K) will display a broken image.

 *** note
 _Inline image caching_

 Gitiles allows browsers to locally cache rendered markdown pages.
 Cache invalidation is triggered by the markdown file being modified
 and having a different SHA-1 in Git.  Inlined images may need a
 documentation file update to be refreshed when viewed through unstable
 URLs like `/docs/+/master/index.md`.
 ***

 ### HTML

 Most HTML tags are not supported.  HTML will be dropped on the floor
 by the parser with no warnings, and no output from that section of the
 document.

 There are small exceptions for `<br>`, `<hr>`, `<a name>` and
 `<iframe>` elements, see [named anchor](#Named-anchors) and
 [HTML IFrame](#HTML-IFrame).

 ## Markdown extensions

 Gitiles includes additional extensions to the Markdown language that
 make documentation writing for the web easier without using raw HTML.

 ### Table of contents

 Place `[TOC]` surrounded by blank lines to insert a generated
 table of contents extracted from the H1, H2, and H3 headers
 used within the document:

 ```
 # Title

 [TOC]

 ## Section 1
 Blah blah...

 ## Section 2
 Go on...
 ```

 H1 headers are omitted from the table of contents if there is only one
 level one header present.  This allows H1 to be used as the document
 title without creating an unnecessary entry in the table of contents.

 Anchors are automatically extracted from the headers, see
 [named anchors](#Named-anchors).

 ### Notification, aside, promotion blocks

 Similar to fenced code blocks these blocks start and end with `***`,
 are surrounded by blank lines, and include the type of block on the
 opening line.

 #### Note

 ```
 *** note
 **Warning:** watch out for nested formatting.
 ***
 ```

 *** note
 **Warning:** watch out for nested formatting.
 ***

 #### Aside

 ```
 *** aside
 An aside can stand off less interesting text.
 ***
 ```

 *** aside
 An aside can stand off less interesting text.
 ***

 #### Promo

 ```
 *** promo
 Promotions can raise awareness of an important concept.
 ***
 ```

 *** promo
 Promotions can raise awareness of an important concept.
 ***

 ### Column layout

 Gitiles markdown includes support for up to 12 columns of text across
 the width of the page.  By default space is divided equally between
 the columns.

 |||---|||
 #### Columns

 can save space.

 #### Prettify

 the page layout.

 *** promo
 #### Can be

 trendy.
 ***
 |||---|||

 A column layout is denoted by a block starting and ending with the
 sequence `|||---|||`.  Within the layout a new column is started for
 each header or note/promo/aside block and all text and formatting flow
 into that column until a new column is started.

 ```
 |||---|||
 #### Columns

 can save space.

 #### Prettify

 the page layout.

 *** promo
 #### Can be

 trendy.
 ***
 |||---|||
 ```

 Column spans can be specified on the first line as a comma separated
 list.  In the example below the first column is 4 wide or 4/12ths of
 the page width, the second is 2 wide (or 2/12ths) and the final column
 is 6 wide (6/12ths or 50%) of the page.

 ```
 |||---||| 4,2,6
 ```

 An empty column can be inserted by prefixing its width with `:`,
 for example shifting content onto the right by padding 6 columns
 on the left:

 ```
 |||---||| :6,3
 #### Right
 |||---|||
 ```

 renders as:

 |||---||| :6,3
 #### Right
 |||---|||

 ### HTML IFrame

 Although HTML is stripped the parser has special support for a limited
 subset of `<iframe>` elements:

 ```
 <iframe src="https://example.com/embed" height="200px" width="400px"></iframe>
 ```

 The parser allows whitespace including newlines between attributes,
 but strictly limits the supported attribute set to:

 src
 : An `https://` or `http://` URL of the page to embed inside of an
 iframe at this position in the document.  Malformed URLs will cause
 the iframe to be silently dropped.  _(required)_

 height
 : CSS pixel height such as `250px` defining the amount of vertical
 space to give to the embedded content.  Only `px` units are supported;
 a malformed dimension will drop the iframe.  _(required)_

 width
 : CSS pixel width such as `250px` or a precentage such as `80%`
 defining the amount of horizontal space to give to the embedded
 content.  Only `px` units or `%` are supported; a malformed dimension
 will drop the iframe.  _(required)_

 frameborder
 : By default a border is drawn around the iframe by the browser.  The
 border can be hidden by adding `frameborder="0"` to the iframe tag.
 _(optional)_

 Embedded source URLs must also be whitelisted by the Gitiles
 `markdown.allowiframe` configuration variable.

 ## Site layout

 Gitiles includes additional support to create functional documentation
 sites served directly from Git repositories.

 ### Navigation bar

 A top level navigation bar is automatically included on all pages if
 there is a `navbar.md` file present in the top of the repository.
 This file should be a simple bulleted list of links to include in the
 navigation bar.

 ```
 * [Home](/index.md)
 * [Markdown](/docs/markdown.md)
 * [Configuration](/docs/configuration.md)
 ```

 Links are resolved relative to the current page, not `navbar.md`.
 Links to other files within the repository should use absolute paths
 to ensure they are resolved correctly from any Markdown file within
 the repository.

 ### Site title

 A site-wide banner is displayed on all Markdown pages if `navbar.md`
 includes an H1 header.  The text of the header is displayed on the
 left side of the banner.

 ```
 # Gitiles

 * [Home](/index.md)
 ```

 ### Site logo

 An optional logo image is displayed in the banner to the left of the
 site title if a `[logo]` reference exists in `navbar.md`. This image
 should be no taller than 45 px.

 ```
 # Gitiles

 [logo]: /images/site_logo.png
 ```

 See [images](#Images) above for acceptable URLs and how repository
 relative paths are handled by inline data URIs.

 ### Home link

 Both the site logo (if present) and site title are wrapped in a link
 if the `[home]` reference is declared in `navbar.md`.  This is
 typically also used in the outline for the navigation bar:

 ```
 # Gitiles

 * [Home][home]
 * [Markdown](/docs/markdown.md)

 [home]: /index.md
 ```

 ### Page title

 Titles for pages are extracted from the first H1 heading appearing in
 the document. This is traditionally placed on the first line of the
 markdown file, e.g.:

 ```
 # Markdown
 ```

 The title is included in the HTML `<title>` element and also in the
 right side of the banner if `navbar.md` defines a
 [site title](#Site-title).

 ## Configuration

 The `gitiles.config` file supporting the site contains several
 configuration options that impact markdown rendering.

 ### Disabling markdown

 Markdown can be completely disabled by setting render to false.

 ```
 [markdown]
   render = false
 ```

 ### Markdown size

 Markdown files are limited by default to 5 MiB of input text
 per file. This limit is configurable, but should not be raised
 beyond available memory.

 ```
 [markdown]
   inputLimit = 5M
 ```

 ### Image size

 Referenced [images are inlined](#Images) as base64 encoded URIs.
 The image limit places an upper bound on the byte size of input.

 ```
 [markdown]
   imageLimit = 256K
 ```

 ### Google Analytics

 [Google Analytics](https://www.google.com/analytics/) can be
 enabled on every rendered markdown page by adding the Property ID
 to the configuration file:

 ```
 [google]
   analyticsId = UA-XXXX-Y
 ```
	# Markdown

	The [Gitiles](https://code.google.com/p/gitiles/) source browser
	automatically renders `*.md` Markdown files into HTML for simplified
	documentation.

	[TOC]

	## Access controls

	Access controls for documentation is identical to source code.

	Documentation stored with source files shares the same permissions.
	Documentation stored in a separate Git repository can use different
	access controls. If Gerrit Code Review is being used, branch level
	read permissions can be used to grant or restrict access to any
	documentation branches.

	## READMEs

	Files named `README.md` are automatically displayed below the file's
	directory listing. For the top level directory this mirrors the
	standard [GitHub](https://github.com/) presentation.

	*** promo
	README.md files are meant to provide orientation for developers
	browsing the repository, especially first-time users.
	***

	We recommend that Git repositories have an up-to-date top-level
	`README.md` file.

	## Markdown syntax

	Gitiles supports the core Markdown syntax described in
	[Markdown Basics]. Additional extensions are supported
	to more closely match [GitHub Flavored Markdown] and
	simplify documentation writing.

	[Markdown Basics]: http://daringfireball.net/projects/markdown/basics
	[GitHub Flavored Markdown]: https://help.github.com/articles/github-flavored-markdown/

	### Paragraphs

	Paragraphs are one or more lines of consecutive text, followed by
	one or more blank lines. Line breaks within a paragraph are ignored
	by the parser, allowing authors to line-wrap text at any comfortable
	column width.

	```
	Documentation writing can be fun and profitable
	by helping users to learn and solve problems.

	After documentation is written, it needs to be published on the
	web where it can be easily accessed for reading.
	```

	### Headings

	Headings can be indicated by starting the line with one or more `#`
	marks. The number of `#` used determines the depth of the heading in
	the document outline. Headings 1 through 6 (`######`) are supported.

	```
	# A level one (H1) heading
	## A level two (H2) heading
	### A level three (H3) heading
	```

	Headings can also use the less popular two line `======` and `------`
	forms to create H1 and H2 level headers:

	```
	A first level header
	====================

	A second level header
	---------------------
	```

	This form is discouraged as maintaining the length of the `===` or
	`---` lines to match the preceding line can be tedious work that is
	unnecessary with the `#` headers.

	### Lists

	A bullet list:

	```
	* Fruit
	* Orange
	* Pear
	* Cake
	```

	will render into HTML as:

	* Fruit
	* Orange
	* Pear
	* Cake

	The second level items (above Orange, Pear) must be indented with more
	spaces than the item they are nested under. Above 2 spaces were used.
	Additionally, the entire list must be preceded and followed by a blank
	line.

	A numbered list:

	```
	1. Fruit
	1. Orange
	2. Pear
	5. Cake
	```

	will render into HTML as:

	1. Fruit
	1. Orange
	2. Pear
	5. Cake

	List items will be renumbered sequentially by the browser, which is
	why `5` above displays as `2`. Even with this feature it is a good
	idea to maintain list item numbers in the source Markdown to simplify
	reading the source file.

	Like bullet lists, numbered lists can be nested by using more leading
	space than the prior list item.

	### Tables

	Simple tables are supported with column alignment. The first line is
	the header row and subsequent lines are data rows:

	```
	\| Food \| Calories \| Tasty? \|
	\|-------\|---------:\|:------:\|
	\| Apple \| 95 \| Yes \|
	\| Pear \| 102 \| Yes \|
	\| Hay \| 977 \| \|
	```

	will render as:

	\| Food \| Calories \| Tasty? \|
	\|-------\|---------:\|:------:\|
	\| Apple \| 95 \| Yes \|
	\| Pear \| 102 \| Yes \|
	\| Hay \| 977 \| \|

	Placing `:` in the separator line indicates how the column should be
	aligned. A colon on the left side is a left-aligned column; a
	colon on the right-most side is right-aligned; a colon on both
	sides is center-aligned.

	Empty table cells are indicated by whitespace between the column
	dividers (`\| \|`) while multiple column cells omit the whitespace.

	### Emphasis

	Emphasize paragraph text with italic and bold styles. Either `_`
	or `*` can be used for italic (1 character) and bold text (2
	characters). This allows styles to be mixed within a statement:

	```
	Emphasize paragraph text with italic and bold text.

	It is _strongly_ encouraged to review documentation for typos.
	```

	It is _strongly_ encouraged to review documentation for typos.

	Emphasis within_words_is_ignored which helps write technical
	documentation. Literal \bold can be forced by prefixing the
	opening `` with \ such as `\bold*`.

	### Strikethrough

	Text can be ~~struck out~~ within a paragraph:

	```
	Text can be ~~struck out~~ within a paragraph.
	```

	Note two tildes are required (`~~`) on either side of the struck out
	section of text.

	### Blockquotes

	Blockquoted text can be used to stand off text obtained from
	another source:

	```
	Sir Winston Churchill once said:

	> A lie gets halfway around the world before the truth has a
	> chance to get its pants on.
	```

	renders as:

	Sir Winston Churchill once said:

	> A lie gets halfway around the world before the truth has a
	> chance to get its pants on.

	### Code (inline)

	Use `backticks` to markup inline code within a paragraph:

	```
	Use `backticks` to markup inline code within a paragraph.
	```

	### Code (blocks)

	Create a fenced code block using three backticks before and after a
	block of code, preceeded and followed by blank lines:

	````
	This is a simple hello world program in C:

	``` c
	#include <stdio.h>

	int main() {
	printf("Hello, World.\n");
	return 0;
	}
	```

	To compile it use `gcc hello.c`.
	````

	Text within a fenced code block is taken verbatim and is not
	processed for Markdown markup.

	Syntax highlighting can optionally be enabled for common languages
	by adding the language name in lowercase on the opening line.
	Supported languages include:

	\|\|\|---\|\|\| 2,2,2,2,4

	#### Scripting
	* bash, sh
	* lua
	* perl
	* python, py
	* ruby
	* tcl

	#### Web
	* css
	* dart
	* html
	* javascript, js
	* json

	#### Compiled
	* basic, vb
	* c
	* cpp (C++)
	* go
	* java
	* pascal
	* scala

	#### Markup
	* tex, latex
	* wiki
	* xml
	* xquery
	* xsl
	* yaml

	#### Other
	* clj (Clojure)
	* erlang
	* hs (Haskell)
	* lisp
	* [llvm](http://llvm.org/docs/LangRef.html)
	* matlab
	* ml (OCaml, SML, F#)
	* r
	* [rd](http://cran.r-project.org/doc/manuals/R-exts.html)
	* rust
	* sql
	* vhdl
	\|\|\|---\|\|\|

	### Horizontal rules

	A horizontal rule can be inserted using GitHub style `--` surrounded
	by blank lines. Alternatively repeating `-` or `*` and space on a
	line will also create a horizontal rule:

	```
	---

	- - - -

	* * * *
	```

	### Links

	Wrap text in `[brackets]` and the link destination in parens
	`(http://...)` such as:

	```
	Visit [this site](http://example.com/) for more examples.
	```

	Links can also use references to obtain URLs from elsewhere in the
	same document. This style can be useful if the same URL needs to be
	mentioned multiple times, is too long to cleanly place within text,
	or the link is within a table cell:

	```
	Search for [markdown style][1] examples.

	[1]: https://www.google.com/?gws_rd=ssl#q=markdown+style+guide
	```

	References can be simplified if the text alone is sufficient:

	```
	Visit [Google] to search the web.

	[Google]: https://www.google.com/
	```

	Automatic hyperlinking can be used where the link text should
	obviously also be the URL:

	```
	Use https://www.google.com/ to search the web.
	```

	Well formed URLs beginning with `https://`, `http://`, and `mailto:`
	are used as written for the link's destination. Malformed URLs may be
	replaced with `#zSoyz` to prevent browser evaluation of dangerous
	content.

	HTML escaping of URL characters such as `&` is handled internally by
	the parser/formatter. Documentation writers should insert the URL
	literally and allow the parser and formatter to make it HTML safe.

	Relative links such as `../src/api.md` are resolved relative to the
	current markdown's file path within the Git repository. Absolute
	links such as `/src/api.md` are resolved relative to the top of the
	enclosing Git repository, but within the same branch or Git commit.
	Links may point to any file in the repository. A link to a `*.md`
	file will present the rendered markdown, while a link to a source file
	will display the syntax highlighted source.

	### Named anchors

	Explicit anchors can be inserted anywhere in the document using
	`<a name="tag"></a>` or `{#tag}`.

	Implicit anchors are automatically created for each
	[heading](#Headings). For example `## Section 1` will have
	the anchor `Section-1`.

	*** note
	Anchor generation

	* letters and digits, after removing accents (á → a)
	* spaces are replaced with hyphens (`-`)
	* other characters are replaced with underscores (`_`)
	* runs of hyphens and underscores are collapsed
	***

	If a document contains the same named subsection under different
	parents the parent anchor will prefix the subsections to
	disambiguate. For example the following document will have anchors
	`Running-Format` and `Coding-Format` and `Libraries` as that subsection
	is unique:

	```
	## Running
	### Format
	## Coding
	### Format
	### Libraries
	```

	When placed in a section header the explicit anchor will override
	the automatic anchor. The following are identical and associate
	the anchor `live-examples` with the section header instead of the
	automaticly generated name `Examples`.

	```
	## Examples {#live-examples}
	## Examples <a name="live-examples"></a>
	```

	### Images

	Similar to links but begin with `!` to denote an image reference:

	```
	![diffy the kung fu review cuckoo](http://commondatastorage.googleapis.com/gerrit-static/diffy-w200.png)
	```

	For images the text in brackets will be included as the alt text for
	screen readers.

	Well formed image URLs beginning with `https://` and `http://` will be
	used as written for the `<img src="...">` attribute. Malformed URLs
	will be replaced with a broken `data:` reference to prevent browsers
	from trying to load a bad destination.

	Relative and absolute links to image files within the Git repository
	(such as `../images/banner.png`) are resolved during rendering by
	inserting the base64 encoding of the image using a `data:` URI. Only
	PNG (`.png`), JPEG (`.jpg` or `.jpeg`) and GIF (`.gif`) image
	formats are supported when referenced from the Git repository.

	Unsupported extensions or files larger than [image size](#Image-size)
	limit (default 256K) will display a broken image.

	*** note
	_Inline image caching_

	Gitiles allows browsers to locally cache rendered markdown pages.
	Cache invalidation is triggered by the markdown file being modified
	and having a different SHA-1 in Git. Inlined images may need a
	documentation file update to be refreshed when viewed through unstable
	URLs like `/docs/+/master/index.md`.
	***

	### HTML

	Most HTML tags are not supported. HTML will be dropped on the floor
	by the parser with no warnings, and no output from that section of the
	document.

	There are small exceptions for `<br>`, `<hr>`, `<a name>` and
	`<iframe>` elements, see [named anchor](#Named-anchors) and
	[HTML IFrame](#HTML-IFrame).

	## Markdown extensions

	Gitiles includes additional extensions to the Markdown language that
	make documentation writing for the web easier without using raw HTML.

	### Table of contents

	Place `[TOC]` surrounded by blank lines to insert a generated
	table of contents extracted from the H1, H2, and H3 headers
	used within the document:

	```
	# Title

	[TOC]

	## Section 1
	Blah blah...

	## Section 2
	Go on...
	```

	H1 headers are omitted from the table of contents if there is only one
	level one header present. This allows H1 to be used as the document
	title without creating an unnecessary entry in the table of contents.

	Anchors are automatically extracted from the headers, see
	[named anchors](#Named-anchors).

	### Notification, aside, promotion blocks

	Similar to fenced code blocks these blocks start and end with `***`,
	are surrounded by blank lines, and include the type of block on the
	opening line.

	#### Note

	```
	*** note
	Warning: watch out for nested formatting.
	***
	```

	*** note
	Warning: watch out for nested formatting.
	***

	#### Aside

	```
	*** aside
	An aside can stand off less interesting text.
	***
	```

	*** aside
	An aside can stand off less interesting text.
	***

	#### Promo

	```
	*** promo
	Promotions can raise awareness of an important concept.
	***
	```

	*** promo
	Promotions can raise awareness of an important concept.
	***

	### Column layout

	Gitiles markdown includes support for up to 12 columns of text across
	the width of the page. By default space is divided equally between
	the columns.

	\|\|\|---\|\|\|
	#### Columns

	can save space.

	#### Prettify

	the page layout.

	*** promo
	#### Can be

	trendy.
	***
	\|\|\|---\|\|\|

	A column layout is denoted by a block starting and ending with the
	sequence `\|\|\|---\|\|\|`. Within the layout a new column is started for
	each header or note/promo/aside block and all text and formatting flow
	into that column until a new column is started.

	```
	\|\|\|---\|\|\|
	#### Columns

	can save space.

	#### Prettify

	the page layout.

	*** promo
	#### Can be

	trendy.
	***
	\|\|\|---\|\|\|
	```

	Column spans can be specified on the first line as a comma separated
	list. In the example below the first column is 4 wide or 4/12ths of
	the page width, the second is 2 wide (or 2/12ths) and the final column
	is 6 wide (6/12ths or 50%) of the page.

	```
	\|\|\|---\|\|\| 4,2,6
	```

	An empty column can be inserted by prefixing its width with `:`,
	for example shifting content onto the right by padding 6 columns
	on the left:

	```
	\|\|\|---\|\|\| :6,3
	#### Right
	\|\|\|---\|\|\|
	```

	renders as:

	\|\|\|---\|\|\| :6,3
	#### Right
	\|\|\|---\|\|\|

	### HTML IFrame

	Although HTML is stripped the parser has special support for a limited
	subset of `<iframe>` elements:

	```
	<iframe src="https://example.com/embed" height="200px" width="400px"></iframe>
	```

	The parser allows whitespace including newlines between attributes,
	but strictly limits the supported attribute set to:

	src
	: An `https://` or `http://` URL of the page to embed inside of an
	iframe at this position in the document. Malformed URLs will cause
	the iframe to be silently dropped. _(required)_

	height
	: CSS pixel height such as `250px` defining the amount of vertical
	space to give to the embedded content. Only `px` units are supported;
	a malformed dimension will drop the iframe. _(required)_

	width
	: CSS pixel width such as `250px` or a precentage such as `80%`
	defining the amount of horizontal space to give to the embedded
	content. Only `px` units or `%` are supported; a malformed dimension
	will drop the iframe. _(required)_

	frameborder
	: By default a border is drawn around the iframe by the browser. The
	border can be hidden by adding `frameborder="0"` to the iframe tag.
	_(optional)_

	Embedded source URLs must also be whitelisted by the Gitiles
	`markdown.allowiframe` configuration variable.

	## Site layout

	Gitiles includes additional support to create functional documentation
	sites served directly from Git repositories.

	### Navigation bar

	A top level navigation bar is automatically included on all pages if
	there is a `navbar.md` file present in the top of the repository.
	This file should be a simple bulleted list of links to include in the
	navigation bar.

	```
	* [Home](/index.md)
	* [Markdown](/docs/markdown.md)
	* [Configuration](/docs/configuration.md)
	```

	Links are resolved relative to the current page, not `navbar.md`.
	Links to other files within the repository should use absolute paths
	to ensure they are resolved correctly from any Markdown file within
	the repository.

	### Site title

	A site-wide banner is displayed on all Markdown pages if `navbar.md`
	includes an H1 header. The text of the header is displayed on the
	left side of the banner.

	```
	# Gitiles

	* [Home](/index.md)
	```

	### Site logo

	An optional logo image is displayed in the banner to the left of the
	site title if a `[logo]` reference exists in `navbar.md`. This image
	should be no taller than 45 px.

	```
	# Gitiles

	[logo]: /images/site_logo.png
	```

	See [images](#Images) above for acceptable URLs and how repository
	relative paths are handled by inline data URIs.

	### Home link

	Both the site logo (if present) and site title are wrapped in a link
	if the `[home]` reference is declared in `navbar.md`. This is
	typically also used in the outline for the navigation bar:

	```
	# Gitiles

	* [Home][home]
	* [Markdown](/docs/markdown.md)

	[home]: /index.md
	```

	### Page title

	Titles for pages are extracted from the first H1 heading appearing in
	the document. This is traditionally placed on the first line of the
	markdown file, e.g.:

	```
	# Markdown
	```

	The title is included in the HTML `<title>` element and also in the
	right side of the banner if `navbar.md` defines a
	[site title](#Site-title).

	## Configuration

	The `gitiles.config` file supporting the site contains several
	configuration options that impact markdown rendering.

	### Disabling markdown

	Markdown can be completely disabled by setting render to false.

	```
	[markdown]
	render = false
	```

	### Markdown size

	Markdown files are limited by default to 5 MiB of input text
	per file. This limit is configurable, but should not be raised
	beyond available memory.

	```
	[markdown]
	inputLimit = 5M
	```

	### Image size

	Referenced [images are inlined](#Images) as base64 encoded URIs.
	The image limit places an upper bound on the byte size of input.

	```
	[markdown]
	imageLimit = 256K
	```

	### Google Analytics

	[Google Analytics](https://www.google.com/analytics/) can be
	enabled on every rendered markdown page by adding the Property ID
	to the configuration file:

	```
	[google]
	analyticsId = UA-XXXX-Y
	```