depot/third_party/nixpkgs/nixos/doc/manual/development/writing-documentation.chapter.md

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# Writing NixOS Documentation {#sec-writing-documentation}
As NixOS grows, so too does the need for a catalogue and explanation of
its extensive functionality. Collecting pertinent information from
disparate sources and presenting it in an accessible style would be a
worthy contribution to the project.
## Building the Manual {#sec-writing-docs-building-the-manual}
The DocBook sources of the [](#book-nixos-manual) are in the
[`nixos/doc/manual`](https://github.com/NixOS/nixpkgs/tree/master/nixos/doc/manual)
subdirectory of the Nixpkgs repository.
You can quickly validate your edits with `make`:
```ShellSession
$ cd /path/to/nixpkgs/nixos/doc/manual
$ nix-shell
nix-shell$ make
```
Once you are done making modifications to the manual, it's important to
build it before committing. You can do that as follows:
```ShellSession
nix-build nixos/release.nix -A manual.x86_64-linux
```
When this command successfully finishes, it will tell you where the
manual got generated. The HTML will be accessible through the `result`
symlink at `./result/share/doc/nixos/index.html`.
## Editing DocBook XML {#sec-writing-docs-editing-docbook-xml}
For general information on how to write in DocBook, see [DocBook 5: The
Definitive Guide](http://www.docbook.org/tdg5/en/html/docbook.html).
Emacs nXML Mode is very helpful for editing DocBook XML because it
validates the document as you write, and precisely locates errors. To
use it, see [](#sec-emacs-docbook-xml).
[Pandoc](http://pandoc.org) can generate DocBook XML from a multitude of
formats, which makes a good starting point. Here is an example of Pandoc
invocation to convert GitHub-Flavoured MarkDown to DocBook 5 XML:
```ShellSession
pandoc -f markdown_github -t docbook5 docs.md -o my-section.md
```
Pandoc can also quickly convert a single `section.xml` to HTML, which is
helpful when drafting.
Sometimes writing valid DocBook is simply too difficult. In this case,
submit your documentation updates in a [GitHub
Issue](https://github.com/NixOS/nixpkgs/issues/new) and someone will
handle the conversion to XML for you.
## Creating a Topic {#sec-writing-docs-creating-a-topic}
You can use an existing topic as a basis for the new topic or create a
topic from scratch.
Keep the following guidelines in mind when you create and add a topic:
- The NixOS [`book`](http://www.docbook.org/tdg5/en/html/book.html)
element is in `nixos/doc/manual/manual.xml`. It includes several
[`parts`](http://www.docbook.org/tdg5/en/html/book.html) which are in
subdirectories.
- Store the topic file in the same directory as the `part` to which it
belongs. If your topic is about configuring a NixOS module, then the
XML file can be stored alongside the module definition `nix` file.
- If you include multiple words in the file name, separate the words
with a dash. For example: `ipv6-config.xml`.
- Make sure that the `xml:id` value is unique. You can use abbreviations
if the ID is too long. For example: `nixos-config`.
- Determine whether your topic is a chapter or a section. If you are
unsure, open an existing topic file and check whether the main
element is chapter or section.
## Adding a Topic to the Book {#sec-writing-docs-adding-a-topic}
Open the parent XML file and add an `xi:include` element to the list of
chapters with the file name of the topic that you created. If you
created a `section`, you add the file to the `chapter` file. If you created
a `chapter`, you add the file to the `part` file.
If the topic is about configuring a NixOS module, it can be
automatically included in the manual by using the `meta.doc` attribute.
See [](#sec-meta-attributes) for an explanation.