Documentation cheat sheet

The documentation files use a mixture of Markdown and MyST syntax.

See the following sections for syntax help and conventions.

Headings

Input	Description
# Title	Page title and H1 heading
## Heading	H2 heading
### Heading	H3 heading
#### Heading	H4 heading
…	Further headings

Adhere to the following conventions:

• Do not use consecutive headings without intervening text.

• Use sentence style for headings (capitalize only the first word).

• Do not skip levels (for example, always follow an H2 with an H3, not an H4).

Inline formatting

Input	Output
{guilabel}`UI element`	UI element
`code`	code
{command}`command`	command
*Italic*	Italic
**Bold**	Bold

Adhere to the following conventions:

• Use italics sparingly. Common uses for italics are titles and names (for example, when referring to a section title that you cannot link to, or when introducing the name for a concept).

• Use bold sparingly. A common use for bold is UI elements (“Click OK”). Avoid using bold for emphasis and rather rewrite the sentence to get your point across.

Code blocks

Start and end a code block with three back ticks:

```

You can specify the code language after the back ticks to enforce a specific lexer, but in many cases, the default lexer works just fine.

Input	Output
``` # Demonstrate a code block code: - example: true ```	# Demonstrate a code block code: - example: true
```yaml # Demonstrate a code block code: - example: true ```	# Demonstrate a code block code: - example: true

To include back ticks in a code block, increase the number of surrounding back ticks:

Input	Output
```` ``` ````	```

Links

How to link depends on if you are linking to an external URL or to another page in the documentation.

External links

For external links, use only the URL, or Markdown syntax if you want to override the link text.

Input	Output
https://linuxcontainers.org/incus	https://linuxcontainers.org/incus
[Incus](https://linuxcontainers.org/incus)	Incus

To display a URL as text and prevent it from being linked, add a <span></span>:

Input	Output
https:/<span></span>/linuxcontainers.org/incus	https://linuxcontainers.org/incus

Internal references

For internal references, both Markdown and MyST syntax are supported. In most cases, you should use MyST syntax though, because it resolves the link text automatically and gives an indication of the link in GitHub rendering.

Referencing a page

To reference a documentation page, use MyST syntax to automatically extract the link text. When overriding the link text, use Markdown syntax.

Input	Output	Output on GitHub	Status
{doc}`index`	Incus	{doc}index	Preferred.
[](index)	Incus		Do not use.
[Incus documentation](index)	Incus documentation	Incus documentation	Preferred when overriding the link text.
{doc}`Incus documentation <index>`	Incus documentation	{doc}Incus documentation <index>	Alternative when overriding the link text.

Adhere to the following conventions:

• Override the link text only when it is necessary. If you can use the document title as link text, do so, because the text will then update automatically if the title changes.

• Never “override” the link text with the same text that would be generated automatically.

Referencing a section

To reference a section within the documentation (on the same page or on another page), you can either add a target to it and reference that target, or you can use an automatically generated anchor in combination with the file name.

Adhere to the following conventions:

• Add targets for sections that are central and a “typical” place to link to, so you expect they will be linked frequently. For “one-off” links, you can use the automatically generated anchors.

• Override the link text only when it is necessary. If you can use the section title as link text, do so, because the text will then update automatically if the title changes.

• Never “override” the link text with the same text that would be generated automatically.

Using a target

You can add targets at any place in the documentation. However, if there is no heading or title for the targeted element, you must specify a link text.

Input	Output	Output on GitHub	Description
(target_ID)=		(target_ID)=	Adds the target target_ID.
{ref}`a_section_target`	Referencing a section	{ref}a_section_target	References a target that has a title.
{ref}`link text <a_random_target>`	link text	{ref}link text <a_random_target>	References a target and specifies a title.
[`option name\](a_random_target)	option name	option name (link is broken)	Use Markdown syntax if you need markup on the link text.

Using an automatically generated anchor

You must use Markdown syntax to use automatically generated anchors. You can leave out the file name when linking within the same file.

Input	Output	Output on GitHub	Description
[](#referencing-a-section)	Referencing a section		Do not use.
[link text](#referencing-a-section)	link text	link text	Preferred when overriding the link text.

Navigation

Every documentation page must be included as a subpage to another page in the navigation.

This is achieved with the toctree directive in the parent page:

```{toctree}
:hidden:

subpage1
subpage2
```

If a page should not be included in the navigation, you can suppress the resulting build warning by putting the following instruction at the top of the file:

---
orphan: true
---

Use orphan pages sparingly and only if there is a clear reason for it.

Lists

Input	Output
- Item 1 - Item 2 - Item 3	Item 1 Item 2 Item 3
1. Step 1 1. Step 2 1. Step 3	Step 1 Step 2 Step 3
1. Step 1 - Item 1 * Subitem - Item 2 1. Step 2 1. Substep 1 1. Substep 2	Step 1 Item 1 Subitem Item 2 Step 2 Substep 1 Substep 2

Adhere to the following conventions:

• In numbered lists, use 1. for all items to generate the step numbers automatically.

• Use - for unordered lists. When using nested lists, you can use * for the nested level.

Definition lists

Input	Output
Term 1 : Definition Term 2 : Definition	Term 1 Definition Term 2 Definition

Tables

You can use standard Markdown tables. However, using the rST list table syntax is usually much easier.

Both markups result in the following output:

Header 1	Header 2
Cell 1 Second paragraph cell 1	Cell 2
Cell 3	Cell 4

Markdown tables

| Header 1                           | Header 2 |
|------------------------------------|----------|
| Cell 1<br><br>2nd paragraph cell 1 | Cell 2   |
| Cell 3                             | Cell 4   |

List tables

```{list-table}
   :header-rows: 1

* - Header 1
  - Header 2
* - Cell 1

    2nd paragraph cell 1
  - Cell 2
* - Cell 3
  - Cell 4
```

Notes

Input	Output
```{note} A note. ```	Note A note.
```{tip} A tip. ```	Tip A tip.
```{important} Important information ```	Important Important information.
```{caution} This might damage your hardware! ```	Caution This might damage your hardware!

Adhere to the following conventions:

• Use notes sparingly.

• Only use the following note types: note, tip, important, caution

• Only use a caution if there is a clear hazard of hardware damage or data loss.

Images

Input	Output
```{figure} https://linuxcontainers.org/incus/docs/main/_static/tag.png :width: 100px :alt: Alt text Figure caption ```	Figure caption

Adhere to the following conventions:

• For pictures in the doc directory, start the path with / (for example, /images/image.png).

• Use PNG format for screenshots and SVG format for graphics.

Reuse

A big advantage of MyST in comparison to plain Markdown is that it allows to reuse content.

Substitution

To reuse sentences or paragraphs without too much markup and special formatting, use substitutions.

Substitutions can be defined in the following locations:

• In the substitutions.yaml file. Substitutions defined in this file are available in all documentation pages.

• At the top of a single file in the following format:

  ---
  myst:
    substitutions:
      reuse_key: "This is **included** text."
      advanced_reuse_key: "This is a substitution that includes a code block:
                         ```
                         code block
                         ```"
  
  ---
  

You can combine both options by defining a default substitution in reuse/substitutions.py and overriding it at the top of a file.

Input	Output
{{reuse_key}}	This is included text.
{{advanced_reuse_key}}	This is a substitution that includes a code block: code block

Adhere to the following convention:

• Substitutions do not work on GitHub. Therefore, use key names that indicate the included text (for example, note_not_supported instead of reuse_note).

File inclusion

To reuse longer sections or text with more advanced markup, you can put the content in a separate file and include the file or parts of the file in several locations.

You cannot put any targets into the content that is being reused (because references to this target would be ambiguous then). You can, however, put a target right before including the file.

By combining file inclusion and substitutions, you can even replace parts of the included text.

Input

Output

% Include parts of the content from file [../README.md](../README.md) ```{include} ../README.md :start-after: <!-- Include start Incus intro --> :end-before: <!-- Include end Incus intro --> ```

It provides a unified experience for running and managing full Linux systems inside containers or virtual machines. Incus supports images for a large number of Linux distributions (official Ubuntu images and images provided by the community) and is built around a very powerful, yet pretty simple, REST API. Incus scales from one instance on a single machine to a cluster in a full data center rack, making it suitable for running workloads both for development and in production. Incus allows you to easily set up a system that feels like a small private cloud. You can run any type of workload in an efficient way while keeping your resources optimized. You should consider using Incus if you want to containerize different environments or run virtual machines, or in general run and manage your infrastructure in a cost-effective way. You can try Incus online at: https://linuxcontainers.org/incus/try-it/

Adhere to the following convention:

• File inclusion does not work on GitHub. Therefore, always add a comment linking to the included file.

• To select parts of the text, add HTML comments for the start and end points and use :start-after: and :end-before:, if possible. You can combine :start-after: and :end-before: with :start-line: and :end-line: if required. Using only :start-line: and :end-line: is error-prone though.

Tabs

Input	Output
````{tabs} ```{group-tab} Tab 1 Content Tab 1 ``` ```{group-tab} Tab 2 Content Tab 2 ``` ````	Tab 1Tab 2 Content Tab 1

Collapsible sections

There is no support for details sections in rST, but you can insert HTML to create them.

Input	Output
<details> <summary>Details</summary> Content </details>	Details Content

Glossary

You can define glossary terms in any file. Ideally, all terms should be collected in one glossary file though, and they can then be referenced from any file.

Input	Output
```{glossary} example term Definition of the example term. ```	example term Definition of the example term.
{term}`example term`	example term

More useful markup

Input	Output
```{versionadded} X.Y ```	Added in version X.Y.
{abbr}`API (Application Programming Interface)`	API

Custom extensions

The documentation uses some custom extensions.

Related links

You can add links to related websites to the sidebar by adding the following field at the top of the page:

relatedlinks: https://github.com/canonical/lxd-sphinx-extensions, [RTFM](https://www.google.com)

To override the title, use Markdown syntax. Note that spaces are ignored; if you need spaces in the title, replace them with  , and include the value in quotes if Sphinx complains about the metadata value because it starts with [.

To add a link to a Discourse topic, add the following field at the top of the page (where 12345 is the ID of the Discourse topic):

discourse: 12345

YouTube links

To add a link to a YouTube video, use the following directive:

Input	Output
```{youtube} https://www.youtube.com/watch?v=iMLiK1fX4I0 :title: Demo ```	▶ Watch on YouTube

The video title is extracted automatically and displayed when hovering over the link. To override the title, add the :title: option.

Spelling exceptions

If you need to use a word that does not comply to the spelling conventions, but is correct in a certain context, you can exempt it from the spelling checker by surrounding it with {spellexception}.

Input	Output
{spellexception}`PurposelyWrong`	PurposelyWrong

Terminal output

To show a terminal view with commands and output, use the following directive:

Input	Output
```{terminal} :input: command number one :user: root :host: vm output line one output line two :input: another command more output ```	root@vm:~# command number one output line oneoutput line two root@vm:~# another command more output

Input is specified as the :input: option (or prefixed with :input: as part of the main content of the directive). Output is the main content of the directive.

To override the prompt (user@host:~$ by default), specify the :user: and/or :host: options. To make the terminal scroll horizontally instead of wrapping long lines, add :scroll:.