Yosys
Table Of Contents
Yosys
Table Of Contents

reStructuredText Primer

reStructuredText is the default plaintext markup language used by Sphinx. This section is a brief introduction to reStructuredText (reST) concepts and syntax, intended to provide authors with enough information to author documents productively. Since reST was designed to be a simple, unobtrusive markup language, this will not take too long.

See also

The authoritative reStructuredText User Documentation. The “ref” links in this document link to the description of the individual constructs in the reST reference.

Paragraphs

The paragraph (:duref:`ref <paragraphs>`) is the most basic block in a reST document. Paragraphs are simply chunks of text separated by one or more blank lines. As in Python, indentation is significant in reST, so all lines of the same paragraph must be left-aligned to the same level of indentation.

Inline markup

The standard reST inline markup is quite simple: use

  • one asterisk: *text* for emphasis (italics),

  • two asterisks: **text** for strong emphasis (boldface), and

  • backquotes: ``text`` for code samples.

If asterisks or backquotes appear in running text and could be confused with inline markup delimiters, they have to be escaped with a backslash.

Be aware of some restrictions of this markup:

  • it may not be nested,

  • content may not start or end with whitespace: * text* is wrong,

  • it must be separated from surrounding text by non-word characters. Use a backslash escaped space to work around that: thisis\ *one*\ word.

These restrictions may be lifted in future versions of the docutils.

It is also possible to replace or expand upon some of this inline markup with roles. Refer to Roles for more information.

Lists and Quote-like blocks

List markup (:duref:`ref <bullet-lists>`) is natural: just place an asterisk at the start of a paragraph and indent properly. The same goes for numbered lists; they can also be autonumbered using a # sign:

* This is a bulleted list.
* It has two items, the second
  item uses two lines.

  • This is a bulleted list.

  • It has two items, the second item uses two lines.

1. This is a numbered list.
2. It has two items too.

  1. This is a numbered list.

  2. It has two items too.

#. This is a numbered list.
#. It has two items too.

  1. This is a numbered list.

  2. It has two items too.

Nested lists are possible, but be aware that they must be separated from the parent list items by blank lines:

* this is
* a list

  * with a nested list
  * and some subitems

* and here the parent list continues

  • this is

  • a list

    • with a nested list

    • and some subitems

  • and here the parent list continues

Definition lists (:duref:`ref <definition-lists>`) are created as follows:

term (up to a line of text)
   Definition of the term, which must be indented

   and can even consist of multiple paragraphs

next term
   Description.
term (up to a line of text)

Definition of the term, which must be indented

and can even consist of multiple paragraphs

next term

Description.

Note that the term cannot have more than one line of text.

Quoted paragraphs (:duref:`ref <block-quotes>`) are created by just indenting them more than the surrounding paragraphs.

Line blocks (:duref:`ref <line-blocks>`) are a way of preserving line breaks:

| These lines are
| broken exactly like in
| the source file.
These lines are
broken exactly like in
the source file.

There are also several more special blocks available:

Literal blocks

Literal code blocks (:duref:`ref <literal-blocks>`) are introduced by ending a paragraph with the special marker ::. The literal block must be indented (and, like all paragraphs, separated from the surrounding ones by blank lines):

This is a normal text paragraph. The next paragraph is a code sample::

   It is not processed in any way, except
   that the indentation is removed.

   It can span multiple lines.

This is a normal text paragraph again.

This is a normal text paragraph. The next paragraph is a code sample:

It is not processed in any way, except
that the indentation is removed.

It can span multiple lines.

This is a normal text paragraph again.

The handling of the :: marker is smart:

  • If it occurs as a paragraph of its own, that paragraph is completely left out of the document.

  • If it is preceded by whitespace, the marker is removed.

  • If it is preceded by non-whitespace, the marker is replaced by a single colon.

That way, the second sentence in the above example’s first paragraph would be rendered as “The next paragraph is a code sample:”.

Code highlighting can be enabled for these literal blocks on a document-wide basis using the highlight directive and on a project-wide basis using the :confval:`highlight_language` configuration option. The code-block directive can be used to set highlighting on a block-by-block basis. These directives are discussed later.

Doctest blocks

Doctest blocks (:duref:`ref <doctest-blocks>`) are interactive Python sessions cut-and-pasted into docstrings. They do not require the literal blocks syntax. The doctest block must end with a blank line and should not end with with an unused prompt:

>>> 1 + 1
2

The doctest appears below,

>>> 1 + 1

Tables

For grid tables (:duref:`ref <grid-tables>`), you have to “paint” the cell grid yourself. They look like this:

+------------------------+------------+----------+----------+
| Header row, column 1   | Header 2   | Header 3 | Header 4 |
| (header rows optional) |            |          |          |
+========================+============+==========+==========+
| body row 1, column 1   | column 2   | column 3 | column 4 |
+------------------------+------------+----------+----------+
| body row 2             | ...        | ...      |          |
+------------------------+------------+----------+----------+

Header row, column 1 (header rows optional)

Header 2

Header 3

Header 4

body row 1, column 1

column 2

column 3

column 4

body row 2

…

…

Simple tables (:duref:`ref <simple-tables>`) are easier to write, but limited: they must contain more than one row, and the first column cells cannot contain multiple lines. They look like this:

=====  =====  =======
A      B      A and B
=====  =====  =======
False  False  False
True   False  False
False  True   False
True   True   True
=====  =====  =======

A

B

A and B

False

False

False

True

False

False

False

True

False

True

True

True

Two more syntaxes are supported: CSV tables and List tables. They use an explicit markup block. Refer to table directives in the Sphinx documentation for more information.

Sections

Section headers (:duref:`ref <sections>`) are created by underlining (and optionally overlining) the section title with a punctuation character, at least as long as the text:

=================
This is a heading
=================

Normally, there are no heading levels assigned to certain characters as the structure is determined from the succession of headings. However, this convention is used in Python’s Style Guide for documenting which you may follow:

  • # with overline, for parts

  • * with overline, for chapters

  • =, for sections

  • -, for subsections

  • ^, for subsubsections

  • ", for paragraphs

Of course, you are free to use your own marker characters (see the reST documentation), and use a deeper nesting level, but keep in mind that most target formats (HTML, LaTeX) have a limited supported nesting depth.

Field Lists

Field lists (:duref:`ref <field-lists>`) are sequences of fields marked up like this:

:fieldname: Field content

They are commonly used in Python documentation:

def my_function(my_arg, my_other_arg):
    """A function just for me.

    :param my_arg: The first of my arguments.
    :param my_other_arg: The second of my arguments.

    :returns: A message (just for me, of course).
    """

Sphinx extends standard docutils behavior and intercepts field lists specified at the beginning of documents. Refer to field lists in the Sphinx documentation for more information.

Roles

A role or “custom interpreted text role” (:duref:`ref <roles>`) is an inline piece of explicit markup. It signifies that that the enclosed text should be interpreted in a specific way. Sphinx uses this to provide semantic markup and cross-referencing of identifiers, as described in the appropriate section. The general syntax is :rolename:`content`.

Docutils supports the following roles:

Refer to roles in the Sphinx documentation for roles added by Sphinx.

Explicit Markup

“Explicit markup” (:duref:`ref <explicit-markup-blocks>`) is used in reST for most constructs that need special handling, such as footnotes, specially-highlighted paragraphs, comments, and generic directives.

An explicit markup block begins with a line starting with .. followed by whitespace and is terminated by the next paragraph at the same level of indentation. (There needs to be a blank line between explicit markup and normal paragraphs. This may all sound a bit complicated, but it is intuitive enough when you write it.)

Directives

A directive (:duref:`ref <directives>`) is a generic block of explicit markup. Along with roles, it is one of the extension mechanisms of reST, and Sphinx makes heavy use of it.

Docutils supports the following directives:

Attention

Attention

Caution

Caution

Danger

Danger

Error

Error

Hint

Hint

Important

Important

Note

Note

Tip

Tip

Warning

Warning

Warning

Do not use the directives :dudir:`sectnum`, :dudir:`header` and :dudir:`footer`.

Directives added by Sphinx are described in directives in the Sphinx documentation.

Basically, a directive consists of a name, arguments, options and content. (Keep this terminology in mind, it is used in the next chapter describing custom directives.) Looking at this example,

.. function:: foo(x)
              foo(y, z)
   :module: some.module.name

   Return a line of text input from the user.

function is the directive name. It is given two arguments here, the remainder of the first line and the second line, as well as one option module (as you can see, options are given in the lines immediately following the arguments and indicated by the colons). Options must be indented to the same level as the directive content.

The directive content follows after a blank line and is indented relative to the directive start.

Images

reST supports an image directive (:dudir:`ref <image>`), used like so:

.. image:: gnu.png
   (options)

When used within Sphinx, the file name given (here gnu.png) must either be relative to the source file, or absolute which means that they are relative to the top source directory. For example, the file sketch/spam.rst could refer to the image images/spam.png as ../images/spam.png or /images/spam.png.

Sphinx will automatically copy image files over to a subdirectory of the output directory on building (e.g. the _static directory for HTML output.)

Interpretation of image size options (width and height) is as follows: if the size has no unit or the unit is pixels, the given size will only be respected for output channels that support pixels. Other units (like pt for points) will be used for HTML and LaTeX output (the latter replaces pt by bp as this is the TeX unit such that 72bp=1in).

Sphinx extends the standard docutils behavior by allowing an asterisk for the extension:

.. image:: gnu.*

Sphinx then searches for all images matching the provided pattern and determines their type. Each builder then chooses the best image out of these candidates. For instance, if the file name gnu.* was given and two files gnu.pdf and gnu.png existed in the source tree, the LaTeX builder would choose the former, while the HTML builder would prefer the latter. Supported image types and choosing priority are defined at Abstract.

Note that image file names should not contain spaces.

Changed in version 0.4: Added the support for file names ending in an asterisk.

Changed in version 0.6: Image paths can now be absolute.

Changed in version 1.5: latex target supports pixels (default is 96px=1in).

Footnotes

For footnotes (:duref:`ref <footnotes>`), use [#name]_ to mark the footnote location, and add the footnote body at the bottom of the document after a “Footnotes” rubric heading, like so:

Lorem ipsum [#f1]_ dolor sit amet ... [#f2]_

.. rubric:: Footnotes

.. [#f1] Text of the first footnote.
.. [#f2] Text of the second footnote.

You can also explicitly number the footnotes ([1]_) or use auto-numbered footnotes without names ([#]_).

Citations

Standard reST citations (:duref:`ref <citations>`) are supported, with the additional feature that they are “global”, i.e. all citations can be referenced from all files. Use them like so:

Lorem ipsum [Ref]_ dolor sit amet.

.. [Ref] Book or article reference, URL or whatever.

Citation usage is similar to footnote usage, but with a label that is not numeric or begins with #.

Substitutions

reST supports “substitutions” (:duref:`ref <substitution-definitions>`), which are pieces of text and/or markup referred to in the text by |name|. They are defined like footnotes with explicit markup blocks, like this:

.. |name| replace:: replacement *text*

or this:

.. |caution| image:: warning.png
             :alt: Warning!

See the :duref:`reST reference for substitutions <substitution-definitions>` for details.

If you want to use some substitutions for all documents, put them into :confval:`rst_prolog` or :confval:`rst_epilog` or put them into a separate file and include it into all documents you want to use them in, using the include directive. (Be sure to give the include file a file name extension differing from that of other source files, to avoid Sphinx finding it as a standalone document.)

Sphinx defines some default substitutions.

Comments

Every explicit markup block which isn’t a valid markup construct (like the footnotes above) is regarded as a comment (:duref:`ref <comments>`). For example:

.. This is a comment.

You can indent text after a comment start to form multiline comments:

..
   This whole indented block
   is a comment.

   Still in the comment.

HTML Metadata

The meta directive (:dudir:`ref <meta>`) allows specifying the HTML metadata element of a Sphinx documentation page. For example, the directive:

.. meta::
   :description: The Sphinx documentation builder
   :keywords: Sphinx, documentation, builder

will generate the following HTML output:

<meta name="description" content="The Sphinx documentation builder">
<meta name="keywords" content="Sphinx, documentation, builder">

Also, Sphinx will add the keywords as specified in the meta directive to the search index. Thereby, the lang attribute of the meta element is considered. For example, the directive:

.. meta::
   :keywords: backup
   :keywords lang=en: pleasefindthiskey pleasefindthiskeytoo
   :keywords lang=de: bittediesenkeyfinden

adds the following words to the search indices of builds with different language configurations:

  • pleasefindthiskey, pleasefindthiskeytoo to English builds;

  • bittediesenkeyfinden to German builds;

  • backup to builds in all languages.

Source encoding

Since the easiest way to include special characters like em dashes or copyright signs in reST is to directly write them as Unicode characters, one has to specify an encoding. Sphinx assumes source files to be encoded in UTF-8 by default; you can change this with the :confval:`source_encoding` config value.

Gotchas

There are some problems one commonly runs into while authoring reST documents:

  • Separation of inline markup: As said above, inline markup spans must be separated from the surrounding text by non-word characters, you have to use a backslash-escaped space to get around that. See :duref:`the reference <substitution-definitions>` for the details.

  • No nested inline markup: Something like *see :func:`foo`* is not possible.

Footnotes

1

When the default domain contains a class directive, this directive will be shadowed. Therefore, Sphinx re-exports it as rst-class.

Table Of Contents