You can quickly check your edits with `nix-build`:
```ShellSession
$ cd /path/to/nixpkgs
$ nix-build doc
```
If the build succeeds, the manual will be in `./result/share/doc/nixpkgs/manual.html`.
### devmode
The shell in the manual source directory makes available a command, `devmode`.
It is a daemon, that:
1. watches the manual's source for changes and when they occur — rebuilds
2. HTTP serves the manual, injecting a script that triggers reload on changes
3. opens the manual in the default browser
## Syntax
As per [RFC 0072](https://github.com/NixOS/rfcs/pull/72), all new documentation content should be written in [CommonMark](https://commonmark.org/) Markdown dialect.
Additional syntax extensions are available, all of which can be used in NixOS option documentation. The following extensions are currently used:
#### Tables
Tables, using the [GitHub-flavored Markdown syntax](https://github.github.com/gfm/#tables-extension-).
#### Anchors
Explicitly defined **anchors** on headings, to allow linking to sections. These should be always used, to ensure the anchors can be linked even when the heading text changes, and to prevent conflicts between [automatically assigned identifiers](https://github.com/jgm/commonmark-hs/blob/master/commonmark-extensions/test/auto_identifiers.md).
It uses the widely compatible [header attributes](https://github.com/jgm/commonmark-hs/blob/master/commonmark-extensions/test/attributes.md) syntax:
> NixOS option documentation does not support headings in general.
#### Inline Anchors
Allow linking arbitrary place in the text (e.g. individual list items, sentences…).
They are defined using a hybrid of the link syntax with the attributes syntax known from headings, called [bracketed spans](https://github.com/jgm/commonmark-hs/blob/master/commonmark-extensions/test/bracketed_spans.md):
```markdown
- []{#ssec-gnome-hooks-glib} `glib` setup hook will populate `GSETTINGS_SCHEMAS_PATH` and then `wrapGAppsHook` will prepend it to `XDG_DATA_DIRS`.
```
#### Automatic links
If you **omit a link text** for a link pointing to a section, the text will be substituted automatically. For example `[](#chap-contributing)`.
This syntax is taken from [MyST](https://myst-parser.readthedocs.io/en/latest/using/syntax.html#targets-and-cross-referencing).
If you want to link to a man page, you can use `` {manpage}`nix.conf(5)` ``. The references will turn into links when a mapping exists in [`doc/manpage-urls.json`](./manpage-urls.json).
A few markups for other kinds of literals are also available:
- `` {command}`rm -rfi` ``
- `` {env}`XDG_DATA_DIRS` ``
- `` {file}`/etc/passwd` ``
- `` {option}`networking.useDHCP` ``
- `` {var}`/etc/passwd` ``
These literal kinds are used mostly in NixOS option documentation.
This syntax is taken from [MyST](https://myst-parser.readthedocs.io/en/latest/syntax/syntax.html#roles-an-in-line-extension-point). Though, the feature originates from [reStructuredText](https://www.sphinx-doc.org/en/master/usage/restructuredtext/roles.html#role-manpage) with slightly different syntax.
#### Admonitions
Set off from the text to bring attention to something.
It uses pandoc’s [fenced `div`s syntax](https://github.com/jgm/commonmark-hs/blob/master/commonmark-extensions/test/fenced_divs.md):
In an effort to keep the Nixpkgs manual in a consistent style, please follow the conventions below, unless they prevent you from properly documenting something.
In that case, please open an issue about the particular documentation convention and tag it with a "needs: documentation" label.
- When showing inputs/outputs of any [REPL](https://en.wikipedia.org/wiki/Read%E2%80%93eval%E2%80%93print_loop), such as a shell or the Nix REPL, use a format as you'd see in the REPL, while trying to visually separate inputs from outputs.
This means that for a shell, you should use a format like the following:
Note how the input is preceded by `$` on the first line and indented on subsequent lines, and how the output is provided as you'd see on the shell.
For the Nix REPL, you should use a format like the following:
```shell
nix-repl> builtins.attrNames { a = 1; b = 2; }
[ "a" "b" ]
```
Note how the input is preceded by `nix-repl>` and the output is provided as you'd see on the Nix REPL.
- When documenting functions or anything that has inputs/outputs and example usage, use nested headings to clearly separate inputs, outputs, and examples.
Keep examples as the last nested heading, and link to the examples wherever applicable in the documentation.
The purpose of this convention is to provide a familiar structure for navigating the manual, so any reader can expect to find content related to inputs in an "inputs" heading, examples in an "examples" heading, and so on.
An example:
```
## buildImage
Some explanation about the function here.
Describe a particular scenario, and point to [](#ex-dockerTools-buildImage), which is an example demonstrating it.
### Inputs
Documentation for the inputs of `buildImage`.
Perhaps even point to [](#ex-dockerTools-buildImage) again when talking about something specifically linked to it.
### Passthru outputs
Documentation for any passthru outputs of `buildImage`.
### Examples
Note that this is the last nested heading in the `buildImage` section.
:::{.example #ex-dockerTools-buildImage}
# Using `buildImage`
Example of how to use `buildImage` goes here.
:::
```
- Use [definition lists](#definition-lists) to document function arguments, and the attributes of such arguments as well as their [types](https://nixos.org/manual/nix/stable/language/values).
This syntax is taken from [CommonMark](https://spec.commonmark.org/0.30/#link-reference-definitions).
#### Typographic replacements
Typographic replacements are enabled. Check the [list of possible replacement patterns check](https://github.com/executablebooks/markdown-it-py/blob/3613e8016ecafe21709471ee0032a90a4157c2d1/markdown_it/rules_core/replacements.py#L1-L15).
If you need documentation-specific help or reviews, ping [@NixOS/documentation-reviewers](https://github.com/orgs/nixos/teams/documentation-reviewers) on your pull request.