=====================
Docutils HTML writers
=====================

.. contents::

html
----

`html` is an alias for the default Docutils HTML writer.
Currently, `html` is mapped to html4css1_.

The target may change with the development of HTML, browsers, Docutils, and
the web.

* Use ``get_writer_by_name('html')`` or the rst2html.py_ front end, if you
  want the output to be up-to-date automatically.

* Use a specific writer name or front end, if you depend on stability of the
  generated HTML code, e.g. because you use a custom style sheet or
  post-processing that may break otherwise.


html4css1
---------

:aliases:    html4, html_
:front-ends: rst2html4.py, rst2html.py_
:config:     `[html4css1 writer]`_

The HTML Writer module, ``docutils/writers/html4css1.py``, was the first
Docutils writer and up to release 0.13 the only official HTML writer.

The output conforms to the `XHTML 1 Transitional`_ specification. It does
not validate as `HTML 4.01 Transitional`_ due to the closing of empty tags
required in XML but not allowed in HTML 4. However, the output follows the
`HTML Compatibility Guidelines`_ for proper rendering on most HTML user
agents.

Correct rendering depends on a CSS_ style sheet. A reference style sheet,
`html4css1.css`_, is provided and used by default.

To support the `Internet Explorer` (with a market share of about 90% around
2002, the time this writer was written), documents contain some hard-coded
formatting hints and are tagged as "text/html" (instead of
"application/xhtml+xml"). [#IE]_

.. [#IE] Conformance to `CSS 2.1`_ has been added in IE 8 (2009), support
   for XHTML in IE 9 (2011).

.. _rst2html.py: tools.html#rst2html-py
.. _[html4css1 writer]: config.html#html4css1-writer
.. _html4css1.css: ../../docutils/writers/html4css1/html4css1.css

pep_html
~~~~~~~~

:front-end: rstpep2html.py_
:config:    `[pep_html writer]`_

This is a special writer for the generation of `Python Enhancement
Proposals`_ (PEPs). It inherits from html4css1_ and adds some `PEP-specific
options`_, a style sheet and template. The front-end uses also a specialised
reader.

.. _rstpep2html.py: tools.html#rstpep2html-py
.. _PEP-specific options:
.. _[pep_html writer]: config.html#pep-html-writer
.. _Python Enhancement Proposals: https://www.python.org/dev/peps/

s5_html
~~~~~~~

:alias:     s5
:front-end: rst2s5.py_
:config:    `[s5_html writer]`_

The `s5` writer inherits from html4css1_. It produces XHTML for use with
S5_, the “Simple Standards-based Slide Show System” by Eric Meyer.  See
`Easy Slide Shows With reST & S5`_ for details.

.. _rst2s5.py: tools.html#rst2s5-py
.. _[s5_html writer]: config.html#s5-html-writer
.. _Easy Slide Shows With reST & S5: slide-shows.html
.. _S5: http://meyerweb.com/eric/tools/s5/
.. _theme: tools.html#themes


html5_polyglot
--------------

:aliases: html5
:front-end: rst2html5.py_
:config: `[html5 writer]`_

The ``html5_polyglot`` writer generates `polyglot HTML`_ [#]_ output, valid
XML [#safetext]_ that is compatible with `HTML5`_. New features and elements
will only be used if they are widely supported to make documents `viewable
with any browser`_.

There is no hard-coded formatting information in the HTML document. Correct
rendering of elements not directly supported by HTML depends on a CSS_ style
sheet. The provided style sheets minimal.css_ and plain.css_ define required
and optional styling rules respectively. Adaption of the layout is possible
with `custom style sheets`_. [#safetext]_

New in Docutils 0.13

.. [#] see also `Benefits of polyglot XHTML5`_
.. [#safetext] The validity of raw HTML and custom stylesheets must be
   ensured by the author (e.g. using `safe text content`_).

.. _rst2html5.py: tools.html#rst2html5-py
.. _[html5 writer]: config.html#html5-writer
.. _minimal.css: ../../docutils/writers/html5_polyglot/minimal.css
.. _plain.css: ../../docutils/writers/html5_polyglot/plain.css
.. _custom style sheets: ../howto/html-stylesheets.html
.. _viewable with any browser: http://www.anybrowser.org/campaign
.. _Benefits of polyglot XHTML5: http://xmlplease.com/xhtml/xhtml5polyglot/
.. _safe text content:
     https://www.w3.org/TR/html-polyglot/#dfn-safe-text-content


HTML writers in the sandbox
---------------------------

There are two more HTML writers in the sandbox_:

.. _sandbox: ../dev/policies.html#the-sandbox

xhtml11
~~~~~~~
:aliases:   xhtml, html4strict
:front-end: rst2xhtml.py
:config:    `[xhtml11 writer]`

`XHTML 1.1`_ is the latest version of the XML based `extensible
Hypertext Markup Language` with an official DTD.

The `xhtml11 writer`_ lives in the Docutils sandbox_ since 2008. The output
conforms to the strict requirements of `XHTML 1.1`_.

.. _xhtml11 writer: ../../../sandbox/html4strict/README.html


html4trans
~~~~~~~~~~

:front-end: rst2html_trans.py_

The `HTML writer for lightweight browsers`_ lives in the Docutils sandbox
(`sandbox/html4trans`_) since 2008. It removes the dependency on CSS. The
output conforms to `XHTML 1 Transitional`_ and contains sufficient
formatting information for rendering without style sheet. (Of course, this
has some drawbacks_.)

.. _HTML writer for lightweight browsers:
   ../../../sandbox/html4trans/README.html
.. _drawbacks: ../../../sandbox/html4trans/README.html#drawbacks
.. _sandbox/html4trans: ../../../sandbox/html4trans
.. _rst2html_trans.py: ../../../sandbox/html4trans/tools/rst2html_trans.py


Overview
--------

=============== =========== ============== ================= ===========
name            alias(es)   `front-end`_   HTML version      CSS version
=============== =========== ============== ================= ===========
html4css1_      html4,      rst2html4.py,  `XHTML 1          `CSS 1`_
                html_       rst2html.py    Transitional`_

pep_html_       ..          rstpep2html.py `XHTML 1          `CSS 1`_
                                           Transitional`_

s5_html_        s5          rst2s5.py      `XHTML 1          `CSS 1`_
                                           Transitional`_

html5_polyglot_ html5       rst2html5.py   `HTML5`_          `CSS 3`_

xhtml11_        xhtml,      rst2xhtml.py   `XHTML 1.1`_      `CSS 3`_
                html4strict

html4trans_ ..              rst2html_trans `XHTML 1          no CSS
                                           Transitional`_    required
=============== =========== ============== ================= ===========


References
----------

_`HTML5`
   `HTML5, A vocabulary and associated APIs for HTML and XHTML`,
   W3C Recommendation, 28 October 2014.
   http://www.w3.org/TR/html5/

_`XHTML 1.1`
   `XHTML™ 1.1 - Module-based XHTML - Second Edition`,
   W3C Recommendation, 23 November 2010.
   http://www.w3.org/TR/xhtml11/

_`XHTML 1 Transitional`
   `Transitional version`_ of:
   `XHTML™ 1.0 The Extensible HyperText Markup Language (Second
   Edition)`, `A Reformulation of HTML 4 in XML 1.0`,
   W3C Recommendation, 26 January 2000, revised 1 August 2002.
   http://www.w3.org/TR/xhtml1/

_`XHTML Basic`
   `XHTML™ Basic 1.1 - Second Edition`,
   W3C Recommendation, 23 November 2010.
   http://www.w3.org/TR/xhtml-basic/

.. _transitional version:
   http://www.w3.org/TR/xhtml1/#a_dtd_XHTML-1.0-Transitional

_`HTML 4.01 Transitional`
  Transitional version of:
  `HTML 4.01 Specification`, W3C Recommendation 24 December 1999.
  http://www.w3.org/TR/html4/

.. _`CSS 1`:

_`CSS Level 1`:
  The features defined in the `CSS1 specification`_, but using the syntax
  and definitions in the `CSS 2.1`_ specification.

_`CSS 2.1` `Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification`,
  W3C Recommendation 07 June 2011.
  http://www.w3.org/TR/CSS21/

_`CSS 3`:
  CSS Level 3 builds on CSS Level 2 module by module, using the CSS2.1
  specification as its core.

  Specifications: http://www.w3.org/Style/CSS/specs.en.html

  Validator: http://jigsaw.w3.org/css-validator/

.. other references
   ----------------

.. _HTML Compatibility Guidelines: http://www.w3.org/TR/xhtml1/#guidelines
.. _CSS: http://www.w3.org/TR/CSS/
.. _CSS1 specification: http://www.w3.org/TR/2008/REC-CSS1-20080411/
.. _polyglot HTML: http://www.w3.org/TR/html-polyglot/

   .. Beware. This specification is no longer in active maintenance and the
      HTML Working Group does not intend to maintain it further.

.. Appendix


      On the question of Polyglot markup, there seems to be little
      consensus. One line of argument suggests that, to the extent that it
      is practical to obey the Robustness principle, it makes sense to do
      so. That is, if you're generating HTML markup for the web, and you can
      generate Polyglot markup that is also directly consumable as XML, you
      should do so. Another line of argument suggests that even under the
      most optimistic of projections, so tiny a fraction of the web will
      ever be written in Polyglot that there's no practical benefit to
      pursuing it as a general strategy for consuming documents from the
      web. If you want to consume HTML content, use an HTML parser that
      produces an XML-compatible DOM or event stream.

      -- https://www.w3.org/TR/html-xml-tf-report/#conclusions

  Further development

  On 2016-05-25, David Goodger wrote:

  > In addition, I'd actually like to see the HTML writer(s) with
  > fully-parameterized classes, i.e. removing hard-coded *classes* as well as
  > formatting. This way, any user who wants to (e.g.) write reST for use with
  > Bootstrap can easily work around any naming conflicts.



  Problems with html4css1 writer:

  1. Limiting ourself to CSS Level 1 requires use of hard-coded HTML
     formatting to get all rST objects mapped to HTML.
     Hard-coded HTML formatting is considered bad practice.

  2. Maths cannot be included in MathML format without rendering a
     hmtl4css1-generated document invalid.

     (XHTML 1.1. is the only member of the "HTML4 family" allowing embedding
     of MathML. However, hard-coded HTML formatting prevents its use.)



  Comparison of current HTML versions
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  XHTML1.1
  """"""""

  +2 XML-based with official DTD
     +1 allows processing with XML-tool-chain
     +1 allows validating against the DTD

  +1 writer exists (in sandbox) and in active use since 2008

  -1 "old" format
  -1 requires to work around restrictions lifted in HTML5
     ("start" argument for enumerated lists, some tags in parsed literal)
     which makes code and documents more complicated

  HTML5
  """""
  +1 more recent
  +1 simpler to write, less restrictions

  +1 writer exists and in active use since 2015

  +1 new page structure elements such as <main>, <section>, <article>,
     <header>, <footer>, <aside>, <nav> and <figure>
     provide better matches for the rst document model.

  -1 new elements not yet supported by many browsers.

  -2 no DTD
     - no proper validation possible (there is an experimental validator)
     - no standard interface to post-processing XML-tools

  -1 two concurring definitions:
     W3C standard and WHATWG "HTML Living Standard".

.. _front-end: tools.html
