.. include:: ../header.rst
=====================
 Docutils Transforms
=====================
:Author: David Goodger
:Contact: docutils-develop@lists.sourceforge.net
:Revision: $Revision: 10166 $
:Date: $Date: 2025年06月16日 11:45:10 +0200 (Mo, 16. Jun 2025) $
:Copyright: This document has been placed in the public domain.
.. contents::
 :depth: 2
Introduction
============
Transforms change the `document tree`_ in-place, add to the tree, or prune it.
Transforms resolve references and footnote numbers, process
`interpreted text`_, and do other context-sensitive processing.
Each transform is a subclass of `docutils.transforms.Transform`.
Most transforms are added by components, others (e.g. `parts.Contents`) are
added by the parser if a corresponding directive_ is found in the document.
To add a transform, components (objects inheriting from
`docutils.Component` like Readers, Parsers, Writers, Input, Output) overwrite
the `get_transforms()` method of their base class. After the Reader has
finished processing, the Publisher calls
`Transformer.populate_from_components()` with a list of components and all
transforms returned by the component's `get_transforms()` method are
stored in a `Transformer` object attached to the document tree.
For more info about transforms and the `Transformer` object,
see also `PEP 258`_. [#]_
.. [#] The `default_transforms()` attribute of component classes mentioned
 in PEP 258 is deprecated. Use the `get_transforms()` method instead.
.. _priority:
Transforms Listed in Priority Order
===================================
Transform classes each have a `default_priority` attribute which is used by
the Transformer to apply transforms in order (low to high). The default
priority can be overridden when adding transforms to the Transformer object.
================================== ============================ ========
Transform: module.Class Added By Priority
================================== ============================ ========
misc_.ClassAttribute `"class"`_ (d/p) _`210`
references_.Substitutions standalone_ (r), pep_ (r) _`220`
references_.PropagateTargets standalone_ (r), pep_ (r) _`260`
frontmatter.\ DocTitle_ standalone_ (r) _`320`
frontmatter.\ DocInfo_ standalone_ (r) _`340`
frontmatter.\ SectSubTitle_ standalone_ (r) _`350`
peps_.Headers pep_ (r) _`360`
peps_.Contents pep_ (r) _`380`
universal_.StripClassesAndElements writers_ (w) _`420`
references_.AnonymousHyperlinks standalone_ (r), pep_ (r) _`440`
references_.IndirectHyperlinks standalone_ (r), pep_ (r) _`460`
peps_.TargetNotes pep_ (r) _`520`
references_.TargetNotes peps.TargetNotes (t/p) 0
misc_.CallBack peps.TargetNotes (t/p) 1
references_.TargetNotes `"target-notes"`_ (d/p) _`540`
references_.Footnotes standalone_ (r), pep_ (r) _`620`
references_.ExternalTargets standalone_ (r), pep_ (r) _`640`
references_.InternalTargets standalone_ (r), pep_ (r) _`660`
parts_.SectNum `"sectnum"`_ (d/p) _`710`
parts_.Contents `"contents"`_ (d/p), _`720`
 peps.Contents (t/p)
universal_.StripComments readers_ (r) _`740`
peps_.PEPZero peps.Headers (t/p) _`760`
references_.CitationReferences latex2e_ (w) _`770`
components.Filter *not used* _`780`
universal_.Decorations readers_ (r) _`820`
misc_.Transitions standalone_ (r), pep_ (r) _`830`
universal_.Validate parsers_ (p) _`835`
universal_.ExposeInternals readers_ (r) _`840`
references_.DanglingReferences standalone_ (r), pep_ (r), _`850`
 *deprecated* [#dangling]_
universal_.SmartQuotes rst_ (p) _`855`
universal_.Messages writers_ (w) _`860`
universal_.FilterMessages writers_ (w) _`870`
universal_.TestMessages DocutilsTestSupport _`880`
writer_aux_.Compound *not used, to be removed* _`910`
writer_aux_.Admonitions `_html_base`_ (w), _`920`
 latex2e_ (w)
misc_.CallBack n/a _`990`
================================== ============================ ========
Key:
* (r): Reader
* (w): Writer
* (d): Directive
* (t): Transform
* (/p): Via a `\<pending>`_ element
.. [#dangling] `references.DanglingReferences` will be replaced by
 separate transforms for resolving refnames__ to refids__
 and for reporting unresolved references to make space for
 reference-resolving transforms added by extensions or applications
 (cf. `Release Notes`__).
 __ ../ref/doctree.html#refname
 __ ../ref/doctree.html#refid
 __ ../../RELEASE-NOTES.html#removals
Transform Priority Range Categories
-----------------------------------
==== ==== ================================================
 Priority
---------- ------------------------------------------------
From To Category
==== ==== ================================================
 0 99 immediate execution (added by another transform)
 100 199 very early (non-standard)
 200 299 very early
 300 399 early
 400 699 main
 700 799 late
 800 899 very late
 900 999 very late (non-standard)
==== ==== ================================================
Transforms Added by Components
==============================
.. _readers:
readers.Reader:
 &#124; universal.StripComments (740_)
 &#124; universal.Decorations (820_)
 &#124; universal.ExposeInternals (840_)
readers.ReReader:
 None
 .. _standalone:
readers.standalone.Reader:
 &#124; references.Substitutions (220_)
 &#124; references.PropagateTargets (260_)
 &#124; frontmatter.\ DocTitle_ (320_)
 &#124; frontmatter.\ DocInfo_ (340_)
 &#124; frontmatter.\ SectSubTitle_ (350_)
 &#124; references.AnonymousHyperlinks (440_)
 &#124; references.IndirectHyperlinks (460_)
 &#124; references.Footnotes (620_)
 &#124; references.ExternalTargets (640_)
 &#124; references.InternalTargets (660_)
 &#124; misc.Transitions (830_)
 &#124; references.DanglingReferences (850_)
 .. _pep:
readers.pep.Reader:
 &#124; references.Substitutions (220_)
 &#124; references.PropagateTargets (260_)
 &#124; peps.Headers (360_)
 &#124; peps.Contents (380_)
 &#124; references.AnonymousHyperlinks (440_)
 &#124; references.IndirectHyperlinks (460_)
 &#124; peps.TargetNotes (520_)
 &#124; references.Footnotes (620_)
 &#124; references.ExternalTargets (640_)
 &#124; references.InternalTargets (660_)
 &#124; misc.Transitions (830_)
 &#124; references.DanglingReferences (850_)
 .. _parsers:
parsers.Parser
 universal_.Validate (835_)
 .. _rst:
parsers.rst.Parser
 universal.SmartQuotes (855_)
 .. _writers:
writers.Writer:
 &#124; universal.StripClassesAndElements (420_)
 &#124; universal.Messages (860_)
 &#124; universal.FilterMessages (870_)
writers.UnfilteredWriter
 None
 .. _latex2e:
writers.latex2e.Writer
 &#124; writer_aux.Admonitions (920_)
 &#124; references.CitationReferences (770_)
 .. _`_html_base`:
writers._html_base.Writer:
 writer_aux.Admonitions (920_)
writers.odf_odt.Writer:
 removes references.DanglingReferences
Transforms Reference
====================
.. Note:: This section is still incomplete.
See also `Transforms Listed in Priority Order`_
and the sources in `docutils/transforms`__.
__ https://docutils.sourceforge.io/docutils/transforms/
DocInfo
-------
.. class:: field-indent-12em
:Module: frontmatter_
:Added by: standalone_ Reader
:Default priority_: 340_
:Configuration_ setting: docinfo_xform_ (default: True)
Given a document starting [#pre-docinfo]_ with a field list, the DocInfo
transform converts fields with registered `bibliographic field`_ names to
the corresponding document tree elements becoming child elements of the
`\<docinfo>`_ element (except for "dedication" and "abstract", which
become `\<topic>`_ elements after <docinfo>).
.. [#pre-docinfo] A document title and subtitle, header and footer,
 as well as body elements that do not show up in the output
 before the field list don't prevent the DocInfo transformation.
 See the `DocTitle examples`_ and `PreBibliographic Elements`_
 in the Appendix for details.
For example, this document fragment::
 <document>
 <title>
 Document Title
 <field_list>
 <field>
 <field_name>
 Author
 <field_body>
 <paragraph>
 A. Name
 <field>
 <field_name>
 Status
 <field_body>
 <paragraph>
 $RCSfile$
 ...
will be transformed to::
 <document>
 <title>
 Document Title
 <docinfo>
 <author>
 A. Name
 <status>
 frontmatter.py
 ...
DocTitle
--------
.. class:: field-indent-12em
:Module: frontmatter_
:Added by: standalone_ Reader
:Default priority_: 320_
:Configuration_ setting: doctitle_xform_ (default: True)
Under the conditions explained below, the DocTitle transform converts
the document's first section title(s) to a document title and
subtitle.
1. If the document contains a single top-level section as its first body
 element, [#pre-doctitle]_ the top-level section's title is used
 as `document title`_ and default `metadata title`_. The top-level
 section's contents become the document's immediate contents.
 .. _step 2:
2. If step 1 successfully determines the document title, the transform
 checks for a subtitle:
 If the lone top-level section itself contains a single second-level
 section as its first element, [#pre-doctitle]_ that section's
 title is promoted to the document's subtitle, and that section's
 contents become the document's immediate contents.
The transform can be disabled with the doctitle_xform_ configuration
setting or the corresponding ``--no-doc-title`` command line option.
.. [#pre-doctitle] Header and footer as well as body elements that
 do not show up in the output before the section don't stop the
 transformation of the section title to document title or subtitle.
 See `PreBibliographic Elements`_ in the Appendix for details.
.. _DocTitle examples:
Examples
~~~~~~~~
The input text ::
 Top-Level Title
 ===============
 A paragraph.
is parsed to the following document tree::
 <document>
 <section names="top-level\ title">
 <title>
 Top-Level Title
 <paragraph>
 A paragraph.
The DocTitle transform converts it to::
 <document names="top-level\ title" title="Top-Level Title">
 <title>
 Top-Level Title
 <paragraph>
 A paragraph.
Given this input with a lone section and sub-section::
 Top-Level Title
 ===============
 Second-Level Title
 ~~~~~~~~~~~~~~~~~~
 A paragraph.
the result after parsing and running the DocTitle transform is::
 <document names="top-level\ title">
 <title>
 Top-Level Title
 <subtitle names="second-level\ title">
 Second-Level Title
 <paragraph>
 A paragraph.
(Note that the implicit hyperlink target generated by the
"Second-Level Title" is preserved on the "subtitle" element
itself.)
--------------
The following examples do *not* comply with the conditions:
i. More than one top-level section::
 Top-Level Title
 ===============
 A paragraph.
 Another Top-Level Title
 =======================
 Another paragraph.
 The DocTitle transform will leave the document tree as-is.
 The document has no title. It is recommended to set the
 `metadata title`_ with the `"title"`_ directive.
#. More than one second-level section::
 Top-Level Title
 ===============
 Second-Level Title
 ~~~~~~~~~~~~~~~~~~
 A paragraph.
 Another Second-Level Title
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 Another paragraph.
 Step 2 is skipped. "Top-Level Title" becomes the document title;
 "Second-Level Title" and "Another Second-Level Title" become titles of
 top-level sections.
 This is what you normally want in a document with title but no
 subtitle.
#. Body elements before the first section: [#pre-doctitle]_ ::
 .. note:: This element would not stop the transform, if it were
 nested in a header.
 Top-Level Title
 ===============
 A paragraph.
 The DocTitle transform will leave the document tree as-is.
 The document has no title.
#. A `configuration file`_ entry "``doctitle_xform: False``"
 or converting with the CLI command ::
 docutils --no-doc-title example.rst> example.html
 The DocTitle transform is skipped. The document has no title.
SectSubTitle
------------
.. class:: field-indent-12em
:Module: frontmatter_
:Added by: standalone_ Reader
:Default priority_: 350_
:Configuration_ setting: sectsubtitle_xform_ (default: False)
The SectSubTitle transform works like `step 2`_ of the DocTitle_
transform, but for sections.
For example, ::
 <section>
 <title>
 Title
 <section>
 <title>
 Subtitle
 ...
is transformed into ::
 <section>
 <title>
 Title
 <subtitle>
 Subtitle
 ...
This transform is disabled by default.
Appendix
========
PreBibliographic Elements
-------------------------
The document tree elements `\<comment>`_, `\<decoration>`_,
`\<footer>`_, `\<head>
<link rel="stylesheet" href="/common/contrast.css" type="text/css" media="all" />
<meta name="robots" content="noindex,nofollow">
<meta name="robots" content="none">
<meta name="robots" content="noarchive">
<meta name="Googlebot" content="noarchive">
`_, `\<meta>`_, `\<pending>`_, `\<raw>`_,
`\<substitution_definition>`_, `\<subtitle>`_, `\<system_message>`_,
`\<target>`_, and `\<title>`_ are ignored when the DocTitle_ and DocInfo_
transforms check for elements before frontmatter candidates.
This means that in the reStructuredText source, comments_,
`hyperlink targets`_, `substitution definitions`_, and the directives_
`"class"`_, `"default-role"`_, `"footer"`_, `"header"`_, `"meta"`_,
`"raw"`_, `"sectnum"`_, `"sectnum"`_, `"target-notes"`_, and `"title"`_
may be placed before the `document title`_ or `bibliographic fields`_.
The DocTitle_ transform inserts document title and subtitle before these
elements. DocInfo_ inserts the bibliographic fields before
`\<comment>`_, `\<raw>`_, `\<substitution_definition>`_, and `\<target>`_.
For example, the document source::
 .. a comment
 .. &#124;today&#124; date::
 .. _hypertarget: http://example.org
 .. class:: spam
 .. role:: ham
 .. default-role:: ham
 .. footer:: footer text
 .. header:: header text
 .. meta:: :test: value
 .. raw:: html
 raw html text
 .. sectnum::
 .. target-notes::
 .. title:: metadata document title
 Top-Level Title
 ===============
 Second-Level Title
 ~~~~~~~~~~~~~~~~~~
 :date: &#124;today&#124;
is parsed and transformed to::
 <document ids="top-level-title" names="top-level\ title" title="metadata document title">
 <title>
 Top-Level Title
 <subtitle ids="second-level-title" names="second-level\ title">
 Second-Level Title
 <meta content="value" name="test">
 <decoration>
 <header>
 <paragraph>
 header text
 <footer>
 <paragraph>
 footer text
 <docinfo>
 <date>
 2024年03月01日
 <comment xml:space="preserve">
 a comment
 <substitution_definition names="today">
 2024年03月01日
 <target ids="hypertarget" names="hypertarget" refuri="http://example.org">
 <raw classes="spam" format="html" xml:space="preserve">
 raw html text
.. References
 ==========
.. _PEP 258: ../peps/pep-0258.html#transformer
.. _configuration:
.. _configuration file:
.. _configuration setting: ../user/config.html
.. _docinfo_xform: ../user/config.html#docinfo-xform
.. _doctitle_xform: ../user/config.html#doctitle-xform
.. _sectsubtitle_xform: ../user/config.html#sectsubtitle-xform
.. _"class": ../ref/rst/directives.html#class
.. _"contents": ../ref/rst/directives.html#table-of-contents
.. _"default-role": ../ref/rst/directives.html#default-role
.. _"footer": ../ref/rst/directives.html#footer
.. _"header": ../ref/rst/directives.html#header
.. _"meta": ../ref/rst/directives.html#meta
.. _"raw": ../ref/rst/directives.html#raw
.. _"sectnum": ../ref/rst/directives.html#sectnum
.. _"target-notes": ../ref/rst/directives.html#target-notes
.. _"title": ../ref/rst/directives.html#title
.. _document tree: ../ref/doctree.html
.. _`<comment>`: ../ref/doctree.html#comment
.. _`<docinfo>`: ../ref/doctree.html#docinfo
.. _`<decoration>`: ../ref/doctree.html#decoration
.. _`<footer>`: ../ref/doctree.html#footer
.. _`<header>`: ../ref/doctree.html#header
.. _`<meta>`: ../ref/doctree.html#meta
.. _`<pending>`: ../ref/doctree.html#pending
.. _`<raw>`: ../ref/doctree.html#raw
.. _`<substitution_definition>`: ../ref/doctree.html#substitution-definition
.. _`<subtitle>`: ../ref/doctree.html#subtitle
.. _`<system_message>`: ../ref/doctree.html#system-message
.. _`<target>`: ../ref/doctree.html#target
.. _`<title>`: ../ref/doctree.html#title
.. _`<topic>`: ../ref/doctree.html#topic
.. _metadata title: ../ref/doctree.html#title-attribute
.. reStructuredText Markup Specification
.. _bibliographic field:
.. _bibliographic fields: ../ref/rst/restructuredtext.html#bibliographic-fields
.. _comments: ../ref/rst/restructuredtext.html#comments
.. _directive:
.. _directives: ../ref/rst/restructuredtext.html#directives
.. _document title: ../ref/rst/restructuredtext.html#document-title
.. _hyperlink targets: ../ref/rst/restructuredtext.html#hyperlink-targets
.. _interpreted text: ../ref/rst/restructuredtext.html#interpreted-text
.. _registered bibliographic field names:
 ../ref/rst/restructuredtext.html#bibliographic-field-names
.. _substitution definitions:
 ../ref/rst/restructuredtext.html#substitution-definitions
.. transform class sources
.. _frontmatter: ../../docutils/transforms/frontmatter.py
.. _misc: ../../docutils/transforms/misc.py
.. _parts: ../../docutils/transforms/parts.py
.. _peps: ../../docutils/transforms/peps.py
.. _references: ../../docutils/transforms/references.py
.. _universal: ../../docutils/transforms/universal.py
.. _writer_aux: ../../docutils/transforms/writer_aux.py
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