Documentation/doc-guide/sphinx.rst - LeafOS-Devices/android_kernel_samsung_gta4xl - Gitiles

 Introduction
 ============

 The Linux kernel uses `Sphinx`_ to generate pretty documentation from
 `reStructuredText`_ files under ``Documentation``. To build the documentation in
 HTML or PDF formats, use ``make htmldocs`` or ``make pdfdocs``. The generated
 documentation is placed in ``Documentation/output``.

 .. _Sphinx: http://www.sphinx-doc.org/
 .. _reStructuredText: http://docutils.sourceforge.net/rst.html

 The reStructuredText files may contain directives to include structured
 documentation comments, or kernel-doc comments, from source files. Usually these
 are used to describe the functions and types and design of the code. The
 kernel-doc comments have some special structure and formatting, but beyond that
 they are also treated as reStructuredText.

 Finally, there are thousands of plain text documentation files scattered around
 ``Documentation``. Some of these will likely be converted to reStructuredText
 over time, but the bulk of them will remain in plain text.

 .. _sphinx_install:

 Sphinx Install
 ==============

 The ReST markups currently used by the Documentation/ files are meant to be
 built with ``Sphinx`` version 1.3 or upper. If you're desiring to build
 PDF outputs, it is recommended to use version 1.4.6 or upper.

 There's a script that checks for the Spinx requirements. Please see
 :ref:`sphinx-pre-install` for further details.

 Most distributions are shipped with Sphinx, but its toolchain is fragile,
 and it is not uncommon that upgrading it or some other Python packages
 on your machine would cause the documentation build to break.

 A way to get rid of that is to use a different version than the one shipped
 on your distributions. In order to do that, it is recommended to install
 Sphinx inside a virtual environment, using ``virtualenv-3``
 or ``virtualenv``, depending on how your distribution packaged Python 3.

 .. note::

    #) Sphinx versions below 1.5 don't work properly with Python's
       docutils version 0.13.1 or upper. So, if you're willing to use
       those versions, you should run ``pip install 'docutils==0.12'``.

    #) It is recommended to use the RTD theme for html output. Depending
       on the Sphinx version, it should be installed  in separate,
       with ``pip install sphinx_rtd_theme``.

    #) Some ReST pages contain math expressions. Due to the way Sphinx work,
       those expressions are written using LaTeX notation. It needs texlive
       installed with amdfonts and amsmath in order to evaluate them.

 In summary, if you want to install Sphinx version 1.4.9, you should do::

        $ virtualenv sphinx_1.4
        $ . sphinx_1.4/bin/activate
        (sphinx_1.4) $ pip install -r Documentation/sphinx/requirements.txt

 After running ``. sphinx_1.4/bin/activate``, the prompt will change,
 in order to indicate that you're using the new environment. If you
 open a new shell, you need to rerun this command to enter again at
 the virtual environment before building the documentation.

 Image output
 ------------

 The kernel documentation build system contains an extension that
 handles images on both GraphViz and SVG formats (see
 :ref:`sphinx_kfigure`).

 For it to work, you need to install both GraphViz and ImageMagick
 packages. If those packages are not installed, the build system will
 still build the documentation, but won't include any images at the
 output.

 PDF and LaTeX builds
 --------------------

 Such builds are currently supported only with Sphinx versions 1.4 and upper.

 For PDF and LaTeX output, you'll also need ``XeLaTeX`` version 3.14159265.

 Depending on the distribution, you may also need to install a series of
 ``texlive`` packages that provide the minimal set of functionalities
 required for ``XeLaTeX`` to work.

 .. _sphinx-pre-install:

 Checking for Sphinx dependencies
 --------------------------------

 There's a script that automatically check for Sphinx dependencies. If it can
 recognize your distribution, it will also give a hint about the install
 command line options for your distro::

 	$ ./scripts/sphinx-pre-install
 	Checking if the needed tools for Fedora release 26 (Twenty Six) are available
 	Warning: better to also install "texlive-luatex85".
 	You should run:

 		sudo dnf install -y texlive-luatex85
 		/usr/bin/virtualenv sphinx_1.4
 		. sphinx_1.4/bin/activate
 		pip install -r Documentation/sphinx/requirements.txt

 	Can't build as 1 mandatory dependency is missing at ./scripts/sphinx-pre-install line 468.

 By default, it checks all the requirements for both html and PDF, including
 the requirements for images, math expressions and LaTeX build, and assumes
 that a virtual Python environment will be used. The ones needed for html
 builds are assumed to be mandatory; the others to be optional.

 It supports two optional parameters:

 ``--no-pdf``
 	Disable checks for PDF;

 ``--no-virtualenv``
 	Use OS packaging for Sphinx instead of Python virtual environment.


 Sphinx Build
 ============

 The usual way to generate the documentation is to run ``make htmldocs`` or
 ``make pdfdocs``. There are also other formats available, see the documentation
 section of ``make help``. The generated documentation is placed in
 format-specific subdirectories under ``Documentation/output``.

 To generate documentation, Sphinx (``sphinx-build``) must obviously be
 installed. For prettier HTML output, the Read the Docs Sphinx theme
 (``sphinx_rtd_theme``) is used if available. For PDF output you'll also need
 ``XeLaTeX`` and ``convert(1)`` from ImageMagick (https://www.imagemagick.org).
 All of these are widely available and packaged in distributions.

 To pass extra options to Sphinx, you can use the ``SPHINXOPTS`` make
 variable. For example, use ``make SPHINXOPTS=-v htmldocs`` to get more verbose
 output.

 To remove the generated documentation, run ``make cleandocs``.

 Writing Documentation
 =====================

 Adding new documentation can be as simple as:

 1. Add a new ``.rst`` file somewhere under ``Documentation``.
 2. Refer to it from the Sphinx main `TOC tree`_ in ``Documentation/index.rst``.

 .. _TOC tree: http://www.sphinx-doc.org/en/stable/markup/toctree.html

 This is usually good enough for simple documentation (like the one you're
 reading right now), but for larger documents it may be advisable to create a
 subdirectory (or use an existing one). For example, the graphics subsystem
 documentation is under ``Documentation/gpu``, split to several ``.rst`` files,
 and has a separate ``index.rst`` (with a ``toctree`` of its own) referenced from
 the main index.

 See the documentation for `Sphinx`_ and `reStructuredText`_ on what you can do
 with them. In particular, the Sphinx `reStructuredText Primer`_ is a good place
 to get started with reStructuredText. There are also some `Sphinx specific
 markup constructs`_.

 .. _reStructuredText Primer: http://www.sphinx-doc.org/en/stable/rest.html
 .. _Sphinx specific markup constructs: http://www.sphinx-doc.org/en/stable/markup/index.html

 Specific guidelines for the kernel documentation
 ------------------------------------------------

 Here are some specific guidelines for the kernel documentation:

 * Please don't go overboard with reStructuredText markup. Keep it
   simple. For the most part the documentation should be plain text with
   just enough consistency in formatting that it can be converted to
   other formats.

 * Please keep the formatting changes minimal when converting existing
   documentation to reStructuredText.

 * Also update the content, not just the formatting, when converting
   documentation.

 * Please stick to this order of heading adornments:

   1. ``=`` with overline for document title::

        ==============
        Document title
        ==============

   2. ``=`` for chapters::

        Chapters
        ========

   3. ``-`` for sections::

        Section
        -------

   4. ``~`` for subsections::

        Subsection
        ~~~~~~~~~~

   Although RST doesn't mandate a specific order ("Rather than imposing a fixed
   number and order of section title adornment styles, the order enforced will be
   the order as encountered."), having the higher levels the same overall makes
   it easier to follow the documents.

 * For inserting fixed width text blocks (for code examples, use case
   examples, etc.), use ``::`` for anything that doesn't really benefit
   from syntax highlighting, especially short snippets. Use
   ``.. code-block:: <language>`` for longer code blocks that benefit
   from highlighting.


 the C domain
 ------------

 The **Sphinx C Domain** (name c) is suited for documentation of C API. E.g. a
 function prototype:

 .. code-block:: rst

     .. c:function:: int ioctl( int fd, int request )

 The C domain of the kernel-doc has some additional features. E.g. you can
 *rename* the reference name of a function with a common name like ``open`` or
 ``ioctl``:

 .. code-block:: rst

      .. c:function:: int ioctl( int fd, int request )
         :name: VIDIOC_LOG_STATUS

 The func-name (e.g. ioctl) remains in the output but the ref-name changed from
 ``ioctl`` to ``VIDIOC_LOG_STATUS``. The index entry for this function is also
 changed to ``VIDIOC_LOG_STATUS`` and the function can now referenced by:

 .. code-block:: rst

      :c:func:`VIDIOC_LOG_STATUS`


 list tables
 -----------

 We recommend the use of *list table* formats. The *list table* formats are
 double-stage lists. Compared to the ASCII-art they might not be as
 comfortable for
 readers of the text files. Their advantage is that they are easy to
 create or modify and that the diff of a modification is much more meaningful,
 because it is limited to the modified content.

 The ``flat-table`` is a double-stage list similar to the ``list-table`` with
 some additional features:

 * column-span: with the role ``cspan`` a cell can be extended through
   additional columns

 * row-span: with the role ``rspan`` a cell can be extended through
   additional rows

 * auto span rightmost cell of a table row over the missing cells on the right
   side of that table-row.  With Option ``:fill-cells:`` this behavior can
   changed from *auto span* to *auto fill*, which automatically inserts (empty)
   cells instead of spanning the last cell.

 options:

 * ``:header-rows:``   [int] count of header rows
 * ``:stub-columns:``  [int] count of stub columns
 * ``:widths:``        [[int] [int] ... ] widths of columns
 * ``:fill-cells:``    instead of auto-spanning missing cells, insert missing cells

 roles:

 * ``:cspan:`` [int] additional columns (*morecols*)
 * ``:rspan:`` [int] additional rows (*morerows*)

 The example below shows how to use this markup.  The first level of the staged
 list is the *table-row*. In the *table-row* there is only one markup allowed,
 the list of the cells in this *table-row*. Exceptions are *comments* ( ``..`` )
 and *targets* (e.g. a ref to ``:ref:`last row <last row>``` / :ref:`last row
 <last row>`).

 .. code-block:: rst

    .. flat-table:: table title
       :widths: 2 1 1 3

       * - head col 1
         - head col 2
         - head col 3
         - head col 4

       * - column 1
         - field 1.1
         - field 1.2 with autospan

       * - column 2
         - field 2.1
         - :rspan:`1` :cspan:`1` field 2.2 - 3.3

       * .. _`last row`:

         - column 3

 Rendered as:

    .. flat-table:: table title
       :widths: 2 1 1 3

       * - head col 1
         - head col 2
         - head col 3
         - head col 4

       * - column 1
         - field 1.1
         - field 1.2 with autospan

       * - column 2
         - field 2.1
         - :rspan:`1` :cspan:`1` field 2.2 - 3.3

       * .. _`last row`:

         - column 3

 .. _sphinx_kfigure:

 Figures & Images
 ================

 If you want to add an image, you should use the ``kernel-figure`` and
 ``kernel-image`` directives. E.g. to insert a figure with a scalable
 image format use SVG (:ref:`svg_image_example`)::

     .. kernel-figure::  svg_image.svg
        :alt:    simple SVG image

        SVG image example

 .. _svg_image_example:

 .. kernel-figure::  svg_image.svg
    :alt:    simple SVG image

    SVG image example

 The kernel figure (and image) directive support **DOT** formated files, see

 * DOT: http://graphviz.org/pdf/dotguide.pdf
 * Graphviz: http://www.graphviz.org/content/dot-language

 A simple example (:ref:`hello_dot_file`)::

   .. kernel-figure::  hello.dot
      :alt:    hello world

      DOT's hello world example

 .. _hello_dot_file:

 .. kernel-figure::  hello.dot
    :alt:    hello world

    DOT's hello world example

 Embed *render* markups (or languages) like Graphviz's **DOT** is provided by the
 ``kernel-render`` directives.::

   .. kernel-render:: DOT
      :alt: foobar digraph
      :caption: Embedded **DOT** (Graphviz) code

      digraph foo {
       "bar" -> "baz";
      }

 How this will be rendered depends on the installed tools. If Graphviz is
 installed, you will see an vector image. If not the raw markup is inserted as
 *literal-block* (:ref:`hello_dot_render`).

 .. _hello_dot_render:

 .. kernel-render:: DOT
    :alt: foobar digraph
    :caption: Embedded **DOT** (Graphviz) code

    digraph foo {
       "bar" -> "baz";
    }

 The *render* directive has all the options known from the *figure* directive,
 plus option ``caption``.  If ``caption`` has a value, a *figure* node is
 inserted. If not, a *image* node is inserted. A ``caption`` is also needed, if
 you want to refer it (:ref:`hello_svg_render`).

 Embedded **SVG**::

   .. kernel-render:: SVG
      :caption: Embedded **SVG** markup
      :alt: so-nw-arrow

      <?xml version="1.0" encoding="UTF-8"?>
      <svg xmlns="http://www.w3.org/2000/svg" version="1.1" ...>
         ...
      </svg>

 .. _hello_svg_render:

 .. kernel-render:: SVG
    :caption: Embedded **SVG** markup
    :alt: so-nw-arrow

    <?xml version="1.0" encoding="UTF-8"?>
    <svg xmlns="http://www.w3.org/2000/svg"
      version="1.1" baseProfile="full" width="70px" height="40px" viewBox="0 0 700 400">
    <line x1="180" y1="370" x2="500" y2="50" stroke="black" stroke-width="15px"/>
    <polygon points="585 0 525 25 585 50" transform="rotate(135 525 25)"/>
    </svg>
	Introduction
	============

	The Linux kernel uses `Sphinx`_ to generate pretty documentation from
	`reStructuredText`_ files under ``Documentation``. To build the documentation in
	HTML or PDF formats, use ``make htmldocs`` or ``make pdfdocs``. The generated
	documentation is placed in ``Documentation/output``.

	.. _Sphinx: http://www.sphinx-doc.org/
	.. _reStructuredText: http://docutils.sourceforge.net/rst.html

	The reStructuredText files may contain directives to include structured
	documentation comments, or kernel-doc comments, from source files. Usually these
	are used to describe the functions and types and design of the code. The
	kernel-doc comments have some special structure and formatting, but beyond that
	they are also treated as reStructuredText.

	Finally, there are thousands of plain text documentation files scattered around
	``Documentation``. Some of these will likely be converted to reStructuredText
	over time, but the bulk of them will remain in plain text.

	.. _sphinx_install:

	Sphinx Install
	==============

	The ReST markups currently used by the Documentation/ files are meant to be
	built with ``Sphinx`` version 1.3 or upper. If you're desiring to build
	PDF outputs, it is recommended to use version 1.4.6 or upper.

	There's a script that checks for the Spinx requirements. Please see
	:ref:`sphinx-pre-install` for further details.

	Most distributions are shipped with Sphinx, but its toolchain is fragile,
	and it is not uncommon that upgrading it or some other Python packages
	on your machine would cause the documentation build to break.

	A way to get rid of that is to use a different version than the one shipped
	on your distributions. In order to do that, it is recommended to install
	Sphinx inside a virtual environment, using ``virtualenv-3``
	or ``virtualenv``, depending on how your distribution packaged Python 3.

	.. note::

	#) Sphinx versions below 1.5 don't work properly with Python's
	docutils version 0.13.1 or upper. So, if you're willing to use
	those versions, you should run ``pip install 'docutils==0.12'``.

	#) It is recommended to use the RTD theme for html output. Depending
	on the Sphinx version, it should be installed in separate,
	with ``pip install sphinx_rtd_theme``.

	#) Some ReST pages contain math expressions. Due to the way Sphinx work,
	those expressions are written using LaTeX notation. It needs texlive
	installed with amdfonts and amsmath in order to evaluate them.

	In summary, if you want to install Sphinx version 1.4.9, you should do::

	$ virtualenv sphinx_1.4
	$ . sphinx_1.4/bin/activate
	(sphinx_1.4) $ pip install -r Documentation/sphinx/requirements.txt

	After running ``. sphinx_1.4/bin/activate``, the prompt will change,
	in order to indicate that you're using the new environment. If you
	open a new shell, you need to rerun this command to enter again at
	the virtual environment before building the documentation.

	Image output
	------------

	The kernel documentation build system contains an extension that
	handles images on both GraphViz and SVG formats (see
	:ref:`sphinx_kfigure`).

	For it to work, you need to install both GraphViz and ImageMagick
	packages. If those packages are not installed, the build system will
	still build the documentation, but won't include any images at the
	output.

	PDF and LaTeX builds
	--------------------

	Such builds are currently supported only with Sphinx versions 1.4 and upper.

	For PDF and LaTeX output, you'll also need ``XeLaTeX`` version 3.14159265.

	Depending on the distribution, you may also need to install a series of
	``texlive`` packages that provide the minimal set of functionalities
	required for ``XeLaTeX`` to work.

	.. _sphinx-pre-install:

	Checking for Sphinx dependencies
	--------------------------------

	There's a script that automatically check for Sphinx dependencies. If it can
	recognize your distribution, it will also give a hint about the install
	command line options for your distro::

	$ ./scripts/sphinx-pre-install
	Checking if the needed tools for Fedora release 26 (Twenty Six) are available
	Warning: better to also install "texlive-luatex85".
	You should run:

	sudo dnf install -y texlive-luatex85
	/usr/bin/virtualenv sphinx_1.4
	. sphinx_1.4/bin/activate
	pip install -r Documentation/sphinx/requirements.txt

	Can't build as 1 mandatory dependency is missing at ./scripts/sphinx-pre-install line 468.

	By default, it checks all the requirements for both html and PDF, including
	the requirements for images, math expressions and LaTeX build, and assumes
	that a virtual Python environment will be used. The ones needed for html
	builds are assumed to be mandatory; the others to be optional.

	It supports two optional parameters:

	``--no-pdf``
	Disable checks for PDF;

	``--no-virtualenv``
	Use OS packaging for Sphinx instead of Python virtual environment.


	Sphinx Build
	============

	The usual way to generate the documentation is to run ``make htmldocs`` or
	``make pdfdocs``. There are also other formats available, see the documentation
	section of ``make help``. The generated documentation is placed in
	format-specific subdirectories under ``Documentation/output``.

	To generate documentation, Sphinx (``sphinx-build``) must obviously be
	installed. For prettier HTML output, the Read the Docs Sphinx theme
	(``sphinx_rtd_theme``) is used if available. For PDF output you'll also need
	``XeLaTeX`` and ``convert(1)`` from ImageMagick (https://www.imagemagick.org).
	All of these are widely available and packaged in distributions.

	To pass extra options to Sphinx, you can use the ``SPHINXOPTS`` make
	variable. For example, use ``make SPHINXOPTS=-v htmldocs`` to get more verbose
	output.

	To remove the generated documentation, run ``make cleandocs``.

	Writing Documentation
	=====================

	Adding new documentation can be as simple as:

	1. Add a new ``.rst`` file somewhere under ``Documentation``.
	2. Refer to it from the Sphinx main `TOC tree`_ in ``Documentation/index.rst``.

	.. _TOC tree: http://www.sphinx-doc.org/en/stable/markup/toctree.html

	This is usually good enough for simple documentation (like the one you're
	reading right now), but for larger documents it may be advisable to create a
	subdirectory (or use an existing one). For example, the graphics subsystem
	documentation is under ``Documentation/gpu``, split to several ``.rst`` files,
	and has a separate ``index.rst`` (with a ``toctree`` of its own) referenced from
	the main index.

	See the documentation for `Sphinx`_ and `reStructuredText`_ on what you can do
	with them. In particular, the Sphinx `reStructuredText Primer`_ is a good place
	to get started with reStructuredText. There are also some `Sphinx specific
	markup constructs`_.

	.. _reStructuredText Primer: http://www.sphinx-doc.org/en/stable/rest.html
	.. _Sphinx specific markup constructs: http://www.sphinx-doc.org/en/stable/markup/index.html

	Specific guidelines for the kernel documentation
	------------------------------------------------

	Here are some specific guidelines for the kernel documentation:

	* Please don't go overboard with reStructuredText markup. Keep it
	simple. For the most part the documentation should be plain text with
	just enough consistency in formatting that it can be converted to
	other formats.

	* Please keep the formatting changes minimal when converting existing
	documentation to reStructuredText.

	* Also update the content, not just the formatting, when converting
	documentation.

	* Please stick to this order of heading adornments:

	1. ``=`` with overline for document title::

	==============
	Document title
	==============

	2. ``=`` for chapters::

	Chapters
	========

	3. ``-`` for sections::

	Section
	-------

	4. ``~`` for subsections::

	Subsection
	~~~~~~~~~~

	Although RST doesn't mandate a specific order ("Rather than imposing a fixed
	number and order of section title adornment styles, the order enforced will be
	the order as encountered."), having the higher levels the same overall makes
	it easier to follow the documents.

	* For inserting fixed width text blocks (for code examples, use case
	examples, etc.), use ``::`` for anything that doesn't really benefit
	from syntax highlighting, especially short snippets. Use
	``.. code-block:: <language>`` for longer code blocks that benefit
	from highlighting.


	the C domain
	------------

	The Sphinx C Domain (name c) is suited for documentation of C API. E.g. a
	function prototype:

	.. code-block:: rst

	.. c:function:: int ioctl( int fd, int request )

	The C domain of the kernel-doc has some additional features. E.g. you can
	rename the reference name of a function with a common name like ``open`` or
	``ioctl``:

	.. code-block:: rst

	.. c:function:: int ioctl( int fd, int request )
	:name: VIDIOC_LOG_STATUS

	The func-name (e.g. ioctl) remains in the output but the ref-name changed from
	``ioctl`` to ``VIDIOC_LOG_STATUS``. The index entry for this function is also
	changed to ``VIDIOC_LOG_STATUS`` and the function can now referenced by:

	.. code-block:: rst

	:c:func:`VIDIOC_LOG_STATUS`


	list tables
	-----------

	We recommend the use of list table formats. The list table formats are
	double-stage lists. Compared to the ASCII-art they might not be as
	comfortable for
	readers of the text files. Their advantage is that they are easy to
	create or modify and that the diff of a modification is much more meaningful,
	because it is limited to the modified content.

	The ``flat-table`` is a double-stage list similar to the ``list-table`` with
	some additional features:

	* column-span: with the role ``cspan`` a cell can be extended through
	additional columns

	* row-span: with the role ``rspan`` a cell can be extended through
	additional rows

	* auto span rightmost cell of a table row over the missing cells on the right
	side of that table-row. With Option ``:fill-cells:`` this behavior can
	changed from auto span to auto fill, which automatically inserts (empty)
	cells instead of spanning the last cell.

	options:

	* ``:header-rows:`` [int] count of header rows
	* ``:stub-columns:`` [int] count of stub columns
	* ``:widths:`` [[int] [int] ... ] widths of columns
	* ``:fill-cells:`` instead of auto-spanning missing cells, insert missing cells

	roles:

	* ``:cspan:`` [int] additional columns (morecols)
	* ``:rspan:`` [int] additional rows (morerows)

	The example below shows how to use this markup. The first level of the staged
	list is the table-row. In the table-row there is only one markup allowed,
	the list of the cells in this table-row. Exceptions are comments ( ``..`` )
	and targets (e.g. a ref to ``:ref:`last row <last row>``` / :ref:`last row
	<last row>`).

	.. code-block:: rst

	.. flat-table:: table title
	:widths: 2 1 1 3

	* - head col 1
	- head col 2
	- head col 3
	- head col 4

	* - column 1
	- field 1.1
	- field 1.2 with autospan

	* - column 2
	- field 2.1
	- :rspan:`1` :cspan:`1` field 2.2 - 3.3

	* .. _`last row`:

	- column 3

	Rendered as:

	.. flat-table:: table title
	:widths: 2 1 1 3

	* - head col 1
	- head col 2
	- head col 3
	- head col 4

	* - column 1
	- field 1.1
	- field 1.2 with autospan

	* - column 2
	- field 2.1
	- :rspan:`1` :cspan:`1` field 2.2 - 3.3

	* .. _`last row`:

	- column 3

	.. _sphinx_kfigure:

	Figures & Images
	================

	If you want to add an image, you should use the ``kernel-figure`` and
	``kernel-image`` directives. E.g. to insert a figure with a scalable
	image format use SVG (:ref:`svg_image_example`)::

	.. kernel-figure:: svg_image.svg
	:alt: simple SVG image

	SVG image example

	.. _svg_image_example:

	.. kernel-figure:: svg_image.svg
	:alt: simple SVG image

	SVG image example

	The kernel figure (and image) directive support DOT formated files, see

	* DOT: http://graphviz.org/pdf/dotguide.pdf
	* Graphviz: http://www.graphviz.org/content/dot-language

	A simple example (:ref:`hello_dot_file`)::

	.. kernel-figure:: hello.dot
	:alt: hello world

	DOT's hello world example

	.. _hello_dot_file:

	.. kernel-figure:: hello.dot
	:alt: hello world

	DOT's hello world example

	Embed render markups (or languages) like Graphviz's DOT is provided by the
	``kernel-render`` directives.::

	.. kernel-render:: DOT
	:alt: foobar digraph
	:caption: Embedded DOT (Graphviz) code

	digraph foo {
	"bar" -> "baz";
	}

	How this will be rendered depends on the installed tools. If Graphviz is
	installed, you will see an vector image. If not the raw markup is inserted as
	literal-block (:ref:`hello_dot_render`).

	.. _hello_dot_render:

	.. kernel-render:: DOT
	:alt: foobar digraph
	:caption: Embedded DOT (Graphviz) code

	digraph foo {
	"bar" -> "baz";
	}

	The render directive has all the options known from the figure directive,
	plus option ``caption``. If ``caption`` has a value, a figure node is
	inserted. If not, a image node is inserted. A ``caption`` is also needed, if
	you want to refer it (:ref:`hello_svg_render`).

	Embedded SVG::

	.. kernel-render:: SVG
	:caption: Embedded SVG markup
	:alt: so-nw-arrow

	<?xml version="1.0" encoding="UTF-8"?>
	<svg xmlns="http://www.w3.org/2000/svg" version="1.1" ...>
	...
	</svg>

	.. _hello_svg_render:

	.. kernel-render:: SVG
	:caption: Embedded SVG markup
	:alt: so-nw-arrow

	<?xml version="1.0" encoding="UTF-8"?>
	<svg xmlns="http://www.w3.org/2000/svg"
	version="1.1" baseProfile="full" width="70px" height="40px" viewBox="0 0 700 400">
	<line x1="180" y1="370" x2="500" y2="50" stroke="black" stroke-width="15px"/>
	<polygon points="585 0 525 25 585 50" transform="rotate(135 525 25)"/>
	</svg>