############################
ReStructuredText Style Guide
############################
This page describes how reStructuredText (reST) is written for DM documentation through examples.
The :ref:`last section documents our formatting conventions <rst-formatting-guidelines>`.
For more general guides to writing reStructuredText, see Sphinx's `reStructuredText Primer <http://sphinx-doc.org/rest.html#explicit-markup>`_ and the `docutils Quick reStructuredText guide <http://docutils.sourceforge.net/docs/user/rst/quickref.html>`_.
See the pages on :doc:`writing documentation for packages <package_docs>` and :doc:`Python docstrings <py_docs>` for specific reST usage in those contexts.
.. _rst-intro-sample:
Sample
======
.. literalinclude:: rst_sample.rst
:language: rst
:lines: 2-
.. lines field above omits :orphan: field from sample display
:doc:`See this sample rendered <rst_sample>`.
.. _rst-inline-styles:
Inline Text Styling
===================
Italics
``*italic text*`` → *italic text*.
Bold
``**bold text**`` → **bold text**.
Monospace
````monospace text```` → ``monospace text``.
When referring to code objects, it's better to use markup that links to the object's API documentation (see the :ref:`rst-code-link` section).
Inline math
``:math:`\sqrt{16}``` → :math:`\sqrt{16}` (See also the :ref:`Math <rst-math>` section).
.. note::
Inline styles can't be nested
For example, you *can't* write ``*see :ref:`this page <label>`*``.
Inline markup also needs to be surrounded by white space, though trailing punctuation is fine.
You can get around this with an *escaped space* that is otherwise invisible,
For example ``one\ *word*`` renders as one\ *word*.
.. _rst-inline-semantics:
Other semantic markup
---------------------
In addition to the fundamental inline typesetting styles above, you may use additional reST roles to provide semantic meaning to the text.
The documentation's CSS takes advantage of this semantic meaning to provide visual cues to readers.
Abbreviations
``:abbr:`LSST (Large Synoptic Survey Telescope``` → :abbr:`LSST (Large Synoptic Survey Telescope)` (a tool tip exposes the definition)
Filenames and paths
``:file:`repos.yaml``` → :file:`repos.yaml`
Shell commands
``:command:`git rebase -i master``` → :command:`git rebase -i master`
..
FIXME need to clarify that this is actual for linking, no semantics
Environment variables
``:envvar:`EUPS_PATH``` → :envvar:`EUPS_PATH`
User interface labels
``:guilabel:`New Pull Request``` → :guilabel:`New Pull Request`. This markup can be used for button labels, menus, or even text labels in interactive shell programs.
Keyboard commands
``:kbd:`Control-a s``` → :kbd:`Control-a s`. Spell out the keys rather than using Emacs short hand, such as ``C-x``.
To semantically markup Python or C++ code objects, refer to the section on :ref:`rst-code-link`.
.. _rst-lists:
Lists
=====
Unordered lists can be written as:
.. code-block:: rst
- First item
Second paragraph for first item, needs to be consistently indented.
- Second item
- You can put spaces between items, or not.
- Hierarchical lists are also possible
- Put a blank space before the sub-list
- And indent the sub-list consistently
- Last item.
which renders as:
- First item
Second paragraph for first item, needs to be consistently indented.
- Second item
- You can put spaces between items, or not.
- Hierarchical lists are also possible
- Put a blank space before the sub-list
- And indent the sub-list consistently
- Last item.
There should be a blank line before and after the list to separate the list from paragraphs.
Blanks lines are allowed *between* list items as well.
Enumerated lists can be written similarly:
.. code-block:: rst
1. First thing
2. Second thing
or automatically enumerated,
#. First thing
#. Second thing
which renders as:
1. First thing
2. Second thing
or automatically enumerated,
#. First thing
#. Second thing
Definition lists
----------------
Definition lists are terms with an indented content section.
For example:
.. literalinclude:: snippets/def_list.rst
:language: rst
:lines: 3-
produces
.. include:: snippets/def_list.rst
:start-line: 2
Definition lists are not limited to dictionary-like usage; they can be employed whenever a series of terms with associated micro content is needed.
.. _rst-sectioning:
Sections
========
We create section hierarchies as follows:
.. literalinclude:: rst_section_sample.rst
:language: rst
:lines: 2-
.. lines field above omits :orphan: field from sample display
:doc:`See this sample rendered <rst_section_sample>`.
This specific sequence of section markup styles is not mandated by the reST specification, but we encourage you to use it for consistency across all DM reST documents.
**Sections in Python docstrings are a special case.**
First, :ref:`we do not place a blank space between a section header and the object lists below <py-docstring-nospace-headers>`.
Second, :ref:`Python docstrings can only use subsection and subsubsection-level headings <py-docstring-section-levels>`.
.. _rst-linking:
Linking
=======
.. _rst-external-links:
External links
--------------
Links to external web pages can be made two ways.
The first way is:
.. code-block:: rst
When writing Python, it's a good idea to use the `PEP8 style guide`_.
.. _PEP8 style guide: https://www.python.org/dev/peps/pep-0008/
The link reference should be provided directly following the paragraph to make it easier for editors to ensure the text in backticks matches the link reference line.
Despite this fragility, this style is good since it makes the reST itself more readable.
The second method is to put the URL inline:
.. code-block:: rst
When writing Python, it's a good idea to use the
`PEP8 style guide <https://www.python.org/dev/peps/pep-0008/>`_.
You may decide to use either method, taking readability into consideration.
.. _rst-internal-links:
Internal links to labels
------------------------
Any content block can be labeled.
For example, to give a section the label ``making-labels``, we write:
.. code-block:: rst
.. _making-labels:
Making Labels
-------------
Labels are an empty directive that appear directly before any block, such
as a section, image, table, or code block.
Labels start with an underscore, and words in labels are separated by
hyphens.
Labels are a **global namespace**, so make them as specific as possible.
With the ``:ref:`` role you can link to a labeled block:
.. code-block:: rst
For internal links, :ref:`you'll need to make labels <making-labels>`.
You can also make references with ``:ref:`label-name``` and the link text will automatically be populated with the section title or figure caption, for example.
.. _rst-doc-link:
Internal links to other pages
-----------------------------
To link to another page in the same doc project, use the ``:doc:`` role with the **relative path** to the target ``.rst`` document.
.. code-block:: rst
See our :doc:`Styleguide <rst_styleguide>` to learn how to write reST docs.
Note how the ``.rst`` extension wasn't included.
Links to equations
------------------
Equations can be linked to using a ``:ref:`` to their label, as described above.
If the equation with numbered by adding a ``:label:`` field to the math directive itself then that equation can be reference with the ``:eq:`` role.
See :ref:`rst-math-block-refs` for more information.
.. _rst-code-link:
Links to code objects
---------------------
When describing a code object, you can also link to that object's API definition using a syntax similar to the ``:ref:`` role used above.
.. _rst-python-link:
Links to Python objects
^^^^^^^^^^^^^^^^^^^^^^^
Objects can be referenced with these roles:
- ``:py:mod:`package.module``` references a module *or package* with namespace ``package.module``.
- ``:py:func:`pkg.mod.function``` references a Python function at namespace ``pkg.mod.function``.
The role's text does not need to include trailing parentheses.
- ``:py:class:`pkg.mod.Class``` to reference a class ``Class`` in ``pkg.mod``.
- ``:py:meth:`pkg.mod.Class.method``` to reference a method ``method`` in class ``Class`` in ``pkg.mod``.
- ``:py:attr:`pkg.mod.Class.attribute``` to reference an attribute ``attribute`` in class ``Class`` in ``pkg.mod``.
- ``:py:data:`pkg.mod.VARIABLE``` to reference a module-level variable ``VARIABLE`` in ``pkg.mod``.
- ``:py:const:`pkg.mod.CONSTANT``` to reference a module-level *constant* ``CONSTANT`` in ``pkg.mod``.
Namespace resolution
""""""""""""""""""""
In these examples, the full namespace of each Python object is specified.
In some contexts, Sphinx may be able to identify the reference object without the full namespace.
For example in class docstrings, references to methods or attributes in the same class can be made by name alone.
See the `Sphinx documentation <http://sphinx-doc.org/domains.html#cross-referencing-python-objects>`_ for more details on object resolution.
.. _rst-cpp-links:
Links to C++ objects
^^^^^^^^^^^^^^^^^^^^
Similarly to Python object links, Sphinx supports a ``cpp`` domain for C++ code that provides the following roles:
- ``:cpp:class:``
- ``:cpp:func:``
- ``:cpp:member:``
- ``:cpp:var:``
- ``:cpp:type:``
- ``:cpp:enum:``
- ``:cpp:enumerator:``
Note that Sphinx has several limitations for linking to C++ objects:
- A specific version of an overloaded function/method cannot be specified.
- You must escape the opening angle bracket in template classes,
e.g. ``:cpp:class:`ClassName\<T>```.
- You cannot link to template classes/functions/aliases/variables---only template instantiations.
Customizing the link text
^^^^^^^^^^^^^^^^^^^^^^^^^
By default the full namespace to the object is shown as the linked text.
To show only the name of the object itself, prefix the namespace with ``~``.
For example:
.. code-block:: rst
:py:func:`~numpy.sin`
will be rendered as `sin() <#>`_.
As with the ``:ref:`` role, it is also possible to provide custom link text.
For example:
.. code-block:: rst
:py:func:`Numpy's sine function <numpy.sin>`
Default domains
^^^^^^^^^^^^^^^
By default, these code referencing roles require a *domain prefix* such as ``py`` or ``cpp`` to specify the language of the object being reference.
This prefix can be omitted when the domain is implicitly set, such as in a Python docstring.
In a reStructuredText document, the domain can be set via the ``default-domain`` directive.
For example, to set the default domain for a reST document to Python, use
.. code-block:: py
.. default-domain:: py
When this is set, Python code references can be made more concise, e.g., ``:func:`numpy.sin```.
See `Sphinx's documentation on Domains`_ for more information about referencing code objects.
.. _Sphinx's documentation on Domains: http://sphinx-doc.org/domains.html
.. _rst-tables:
Tables
======
We recommend that you use the *grid* syntax for tables, since they more flexible than `'simple' reST tables`_.
And although not necessary, we suggest that you provide a caption using the ``table`` directive and a label prefixed with "``table-``."
For example:
.. _`'simple' rest tables`: http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#simple-tables
.. literalinclude:: snippets/basic_table.rst
:language: rst
:lines: 3-
produces:
.. include:: snippets/basic_table.rst
:start-line: 5
Note how cells can be joined by omitting the dividing line.
The ``=`` characters divide the header from table content.
Text in the header is set in bold.
You can write tables with multiple header rows, including spans across header cells:
.. literalinclude:: snippets/multi_header_table.rst
:language: rst
:lines: 3-
produces:
.. include:: snippets/multi_header_table.rst
:start-line: 5
In the simplest cases, tables are not required to have headers, or even be inside a ``table`` directive.
.. literalinclude:: snippets/noheader_table.rst
:language: rst
:lines: 3-
produces:
.. include:: snippets/noheader_table.rst
:start-line: 2
Be sure to leave a blank line before and after the ``table`` directive.
.. _rst-figures:
Images and Figures
==================
Plain images
------------
Plain images can be included with the ``image`` directive.
For example:
.. literalinclude:: snippets/image.rst
:language: rst
:lines: 3-
.. include:: snippets/image.rst
:start-line: 2
This example shows how an image can by hyperlinked to any URL with the ``target`` field.
Internal links, as in the example, must be *relative* to the reST document; Sphinx does not process URLs in an ``image``\ 's ``target`` field.
The ``image`` directive has `more configurable fields <http://docutils.sourceforge.net/docs/ref/rst/directives.html#image>`_.
If image sizes need to be manipulated from reST, we recommend using ``scale`` since it is responsive.
We hope to provide better support for responsive image sizing.
Be sure to leave a blank line before and after the ``image`` directive.
Figure directive
----------------
Figures include both an image and a caption.
For example:
.. literalinclude:: snippets/figure.rst
:language: rst
:lines: 3-
.. include:: snippets/figure.rst
:start-line: 2
Note that the ``:name:`` field takes the place of a separate :ref:`label <rst-internal-links>` for hyperlinking.
By convention, these labels should be prefixed with "``fig-``."
Be sure to leave a blank line before and after the ``figure`` directive.
Note on paths to image files
----------------------------
Images are included in the ``_static/`` directory of the git repository for this documentation project.
Sphinx requires image assets to be located in this ``_static/`` directory in order to properly copy files into the built website.
By using a prefix "``/``" we indicate that a path is relative to the root of the documentation repository.
Package documentation is hosted in ``doc/`` directories of the git repositories of individual Stack packages.
For such package documentation, image files should be placed inside a directory in ``doc/_static/`` named for the package itself.
For example ``doc/_static/obs_decam/`` for the `obs\_decam <https://github.com/lsst/obs_decam>`_ package.
This nested directory structure is needed to merge package documentation content into the root documentation build.
.. _rst-math:
Math
====
Sphinx allows you to write math expressions with a LaTeX-like plain text syntax that will be typeset by `MathJax <https://www.mathjax.org>`_ in the browser.
MathJax supports AMSMath-LaTeX syntax.
`This website by Dr Carol Burns <http://www.onemathematicalcat.org/MathJaxDocumentation/TeXSyntax.htm>`_ provides a comprehensive listing of available LaTeX syntax in MathJax, along with examples.
In Sphinx, you can either write *inline* expressions with the ``math`` role, or *block* elements with the ``math`` directive.
.. _rst-math-inline:
Inline math
-----------
Write inline math expressions with the ``math`` role.
For example, ``:math:`\sigma_\mathrm{mean} = \sigma / \sqrt{N}``` produces :math:`\sigma_\mathrm{mean} = \sigma / \sqrt{N}`.
.. _rst-math-block:
Block math
----------
To display math as a block element, use the ``math`` directive (be sure to leave a blank line before and after the ``math`` directive).
For example:
.. literalinclude:: snippets/math.rst
:language: rst
:lines: 3-
renders as
.. include:: snippets/math.rst
:start-line: 2
.. _rst-math-block-refs:
Referencing equations
^^^^^^^^^^^^^^^^^^^^^
Notice the ``:label:`` field in the previous sample; it both annotates the equation with a number, and allows the equation to be cross-referenced with the ``eq`` role; for example ```:eq:`math-sample``` produces :eq:`math-sample`.
Equation references may only be made within the same reStructuredText page as the original ``math`` directive.
See `the Sphinx docs on Math support <http://www.sphinx-doc.org/en/stable/ext/math.html>`_ for more information.
.. _rst-math-block-multi:
Multiple Equations
^^^^^^^^^^^^^^^^^^
Multiple equations can appear in the same ``math`` directive.
Simply include a blank line between each equation (and don't include an equation as a argument of the ``math`` directive itself).
For example:
.. literalinclude:: snippets/math-multi.rst
:language: rst
:lines: 3-
renders as
.. include:: snippets/math-multi.rst
:start-line: 2
.. _rst-math-block-align:
Aligned Equations
^^^^^^^^^^^^^^^^^
Often when there are multiple statements in a ``math`` directive it's desirable to align those statements around the equals sign, for example.
In AMSMath-LaTeX this would be achieved with the ``align`` environment.
In reStructuredText we can accomplish the same in a ``math`` directive:
.. literalinclude:: snippets/math-align.rst
:language: rst
:lines: 3-
renders as
.. include:: snippets/math-align.rst
:start-line: 2
Notice how the alignment point is marked with an ``&`` and ``\\`` is appended to each math statement *except for the last.*
Also note how there are no blank lines *between* math statements.
.. _rst-code-blocks:
Source code
===========
For blocks of code, we prefer the ``code-block`` directive.
This directive has the form
.. code-block:: rst
.. code-block:: <language>
:name: optional-label
:emphasize-lines: <optional lines to highlight>
<code>
where
- ``<language>`` can be `any token understood by Pygments`_, particularly ``py`` (python), ``cpp`` (C++), ``java`` (Java), ``js`` (JavaScript) and ``rst`` (reStructuredText). Specify ``none`` to disable highlighting.
- ``:name:`` is an explicit hyperlink label for the code block.
- ``:emphasize-lines:`` is an optional sequence of lines to highlight. This can be comma-separated, with hyphens to indicate spans.
.. _any token understood by Pygments: http://pygments.org/docs/lexers/
For example:
.. literalinclude:: snippets/py_codeblock_example.rst
:language: rst
:lines: 3-
produces
.. include:: snippets/py_codeblock_example.rst
:start-line: 2
Be sure to leave a blank line before and after the ``code-block`` directive.
.. _rst-literalinclude:
Including source code examples from other files with literalinclude
-------------------------------------------------------------------
The ``code-block`` directive is great for code examples written in the reStructuredText source file itself.
You might also want to show a code sample contained in a separate file.
For this you can use the ``literalinclude`` directive:
.. code-block:: rst
.. literalinclude:: path/to/example.py
:language: py
The source path can either be relative to the reST document or relative to the documentation root by prefixing the path with ``/``.
The ``literalinclude`` directive also supports ``code-block`` fields, such as ``name`` and ``emphasize-lines``.
In addition, you can selective include ranges of lines with the ``lines`` field.
For example, to include only lines 10 -- 20:
.. code-block:: rst
.. literalinclude:: path/to/example.py
:language: py
:lines: 10-20
To omit the first two lines from a file:
.. code-block:: rst
.. literalinclude:: path/to/example.py
:language: py
:lines: 2-
Sophisticated inclusion patterns can be achieved by listing multiple spans, such as ``:lines: 3-10,20-``, which shows the first ten lines and all lines after the 20\ :sup:`th`\ .
When including code example snippets from other files, it may be useful to remove indentation.
Use the ``dedent`` field for that.
For example:
.. code-block:: rst
.. literalinclude:: path/to/example.py
:language: py
:lines: 5-10
:dedent: 4
will show lines 5 -- 10 and remove 4 space characters (presumably because the snippet is inside a Python class or function).
.. _rst-lightweight-code-blocks:
Lightweight syntax for Python code and sessions
-----------------------------------------------
You can markup Python code blocks using a lightweight syntax:
.. code-block:: rst
::
print('hello world!')
Interactive python sections can be marked up as
>>> print('Hello world!')
Hello world!
This lightweight syntax :ref:`is used in Python docstrings <py-docstring-examples>`.
.. _rst-prompts:
Command line prompts
====================
For generic command line prompts, we use the `sphinx-prompt`_ extension so that the prompt character (e.g, ``$``) isn't selectable.
This is great for giving copy-and-paste-ready command line instructions.
.. _sphinx-prompt: https://github.com/sbrunner/sphinx-prompt
For basic bash prompts,
.. code-block:: rst
.. prompt:: bash
mkdir -p hello/world
cd hello/world
produces
.. prompt:: bash
mkdir -p hello/world
cd hello/world
.. _rst-footnotes:
Footnotes
=========
Footnotes should be used sparingly, if at all, in LSST documentation.
Prefer inline hyperlinks to other sections.
If you *do* need footnotes, you can make them as follows:
.. code-block:: rst
This is a line.\ [#label]_
.. [#label] This is the footnote content.
Note that we had to provide an escaped space for the footnote mark occurring after a period.
The footnote content should occur not far from the inline footnote mark; generally provide the footnote content at the end of the section.
.. _rst-citations:
Citations
=========
Citations should be used for scholarly references; use hyperlinks for web native content.
Citations can be made as follows:
.. code-block:: rst
The LSST Project [Ivezic2008]_ will produce 15 TB of images per night.
.. [Ivezic2008] Ivezic et al 2008. *LSST: from Science Drivers to
Reference Design and Anticipated Data Products.*
`arxiv:0805.2366 <http://arxiv.org/abs/0805.2366>`_
Citations are distinguished from footnotes in that the label *does not* begin with a ``#``.
In the future, scholarly citations will be easier to include and more 'latex-like' with our `documenteer`_ Sphinx extensions.
.. _documenteer: https://github.com/lsst-sqre/documenteer
.. _rst-comments:
Comments in ReStructuredText
============================
Provide comments to fellow writers using ``..``,
.. code-block:: rst
.. This is a one-line comment.
..
This is the first of a multi-paragraph comment.
The second paragraph.
Avoid using comments to keep around old or alternate versions of text; prefer using Git version control instead.
.. _rst-formatting-guidelines:
RestructuredText Formatting Conventions
=======================================
Text wrapping
-------------
When writing reST documentation in Python docstrings, documentation lines should be wrapped at lengths of 110 characters for :ref:`consistency with our Python Style Guide <style-guide-py-line-length>`.
.. NOTE: ls.st/rfc-107
For reStructuredText documents (e.g., ``.rst`` files), reST doesn't care about line formatting.
Emacs users, for example, are free to use hard-wrap formatting lines at 72 characters if that helps you write docs.
Whenever possible, we *encourage* you to use soft-wrapping for your text.
This allows others format text columns in their editors as they wish.
As well, the GitHub.com code editor does not have hard-wrap auto-formatting.
Those making doc edits on GitHub.com will tend to use soft-wrap by default (see '`GitHub Flow in the Browser`_').
.. _GitHub Flow in the Browser: https://help.github.com/articles/github-flow-in-the-browser/
When using soft-wrap formatting, you might **write one sentence per line** (i.e., put a line break after each sentence).
As a writer, this has the advantage of making it easier to check the rhythm of your writing, including sentence lengths.
Shorter sentences are easier to read.
`One-sentence-per-line`_ is also semantically correct in the sense of Git.
.. _One-sentence-per-line: https://xkcd.com/1285/
At LSST, we place a **single blank line** between all content blocks, such as directives, paragraphs and lists.
Indentation
-----------
ReStructuredText should be indented consistently with the context, which generally means taking visual alignment cues rather than adhering to a fixed indent width.
In directives, align to the directive's name:
.. code-block:: rst
.. code-block:: python
print('hello world')
In lists, align naturally with the text:
.. code-block:: rst
- First item.
Another paragraph for the first item.
- Second item.
Note how that alignment adapts to numbered lists:
.. code-block:: rst
1. First item.
Another paragraph for the first item.
2. Second item.
For :ref:`argument lists in Python docstrings <py-docstring-parameters>` we indent descriptions by four spaces:
.. code-block:: rst
Parameters
----------
x_coord : float
Particle's x-coordinate.
y_coord : float
Particle's y-coordinate.
.. _rst-encoding:
Encoding and special characters
-------------------------------
LSST's reStructuredText source files should be encoded as UTF-8 unicode.
This means that special characters such as en (–) and em (—) dashes can just be written as such.
We do run a variant of `smartypants`_ in an attempt to convert ``--`` and ``---`` into en and em dashes, respectively, and to covert dumb quotes (``"``) into "typographic" quotes.
.. _smartypants: http://daringfireball.net/projects/smartypants/