symbian-qemu-0.9.1-12/python-2.6.1/Doc/documenting/markup.rst
changeset 1 2fb8b9db1c86
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/symbian-qemu-0.9.1-12/python-2.6.1/Doc/documenting/markup.rst	Fri Jul 31 15:01:17 2009 +0100
@@ -0,0 +1,824 @@
+.. highlightlang:: rest
+
+Additional Markup Constructs
+============================
+
+Sphinx adds a lot of new directives and interpreted text roles to standard reST
+markup.  This section contains the reference material for these facilities.
+Documentation for "standard" reST constructs is not included here, though
+they are used in the Python documentation.
+
+File-wide metadata
+------------------
+
+reST has the concept of "field lists"; these are a sequence of fields marked up
+like this::
+
+   :Field name: Field content
+
+A field list at the very top of a file is parsed as the "docinfo", which in
+normal documents can be used to record the author, date of publication and
+other metadata.  In Sphinx, the docinfo is used as metadata, too, but not
+displayed in the output.
+
+At the moment, only one metadata field is recognized:
+
+``nocomments``
+   If set, the web application won't display a comment form for a page generated
+   from this source file.
+
+
+Meta-information markup
+-----------------------
+
+.. describe:: sectionauthor
+
+   Identifies the author of the current section.  The argument should include
+   the author's name such that it can be used for presentation (though it isn't)
+   and email address.  The domain name portion of the address should be lower
+   case.  Example::
+
+      .. sectionauthor:: Guido van Rossum <guido@python.org>
+
+   Currently, this markup isn't reflected in the output in any way, but it helps
+   keep track of contributions.
+
+
+Module-specific markup
+----------------------
+
+The markup described in this section is used to provide information about a
+module being documented.  Each module should be documented in its own file.
+Normally this markup appears after the title heading of that file; a typical
+file might start like this::
+
+   :mod:`parrot` -- Dead parrot access
+   ===================================
+
+   .. module:: parrot
+      :platform: Unix, Windows
+      :synopsis: Analyze and reanimate dead parrots.
+   .. moduleauthor:: Eric Cleese <eric@python.invalid>
+   .. moduleauthor:: John Idle <john@python.invalid>
+
+As you can see, the module-specific markup consists of two directives, the
+``module`` directive and the ``moduleauthor`` directive.
+
+.. describe:: module
+
+   This directive marks the beginning of the description of a module (or package
+   submodule, in which case the name should be fully qualified, including the
+   package name).
+
+   The ``platform`` option, if present, is a comma-separated list of the
+   platforms on which the module is available (if it is available on all
+   platforms, the option should be omitted).  The keys are short identifiers;
+   examples that are in use include "IRIX", "Mac", "Windows", and "Unix".  It is
+   important to use a key which has already been used when applicable.
+
+   The ``synopsis`` option should consist of one sentence describing the
+   module's purpose -- it is currently only used in the Global Module Index.
+
+   The ``deprecated`` option can be given (with no value) to mark a module as
+   deprecated; it will be designated as such in various locations then.
+
+.. describe:: moduleauthor
+
+   The ``moduleauthor`` directive, which can appear multiple times, names the
+   authors of the module code, just like ``sectionauthor`` names the author(s)
+   of a piece of documentation.  It too does not result in any output currently.
+
+
+.. note::
+
+   It is important to make the section title of a module-describing file
+   meaningful since that value will be inserted in the table-of-contents trees
+   in overview files.
+
+
+Information units
+-----------------
+
+There are a number of directives used to describe specific features provided by
+modules.  Each directive requires one or more signatures to provide basic
+information about what is being described, and the content should be the
+description.  The basic version makes entries in the general index; if no index
+entry is desired, you can give the directive option flag ``:noindex:``.  The
+following example shows all of the features of this directive type::
+
+    .. function:: spam(eggs)
+                  ham(eggs)
+       :noindex:
+
+       Spam or ham the foo.
+
+The signatures of object methods or data attributes should always include the
+type name (``.. method:: FileInput.input(...)``), even if it is obvious from the
+context which type they belong to; this is to enable consistent
+cross-references.  If you describe methods belonging to an abstract protocol,
+such as "context managers", include a (pseudo-)type name too to make the
+index entries more informative.
+
+The directives are:
+
+.. describe:: cfunction
+
+   Describes a C function. The signature should be given as in C, e.g.::
+
+      .. cfunction:: PyObject* PyType_GenericAlloc(PyTypeObject *type, Py_ssize_t nitems)
+
+   This is also used to describe function-like preprocessor macros.  The names
+   of the arguments should be given so they may be used in the description.
+
+   Note that you don't have to backslash-escape asterisks in the signature,
+   as it is not parsed by the reST inliner.
+
+.. describe:: cmember
+
+   Describes a C struct member. Example signature::
+
+      .. cmember:: PyObject* PyTypeObject.tp_bases
+
+   The text of the description should include the range of values allowed, how
+   the value should be interpreted, and whether the value can be changed.
+   References to structure members in text should use the ``member`` role.
+
+.. describe:: cmacro
+
+   Describes a "simple" C macro.  Simple macros are macros which are used
+   for code expansion, but which do not take arguments so cannot be described as
+   functions.  This is not to be used for simple constant definitions.  Examples
+   of its use in the Python documentation include :cmacro:`PyObject_HEAD` and
+   :cmacro:`Py_BEGIN_ALLOW_THREADS`.
+
+.. describe:: ctype
+
+   Describes a C type. The signature should just be the type name.
+
+.. describe:: cvar
+
+   Describes a global C variable.  The signature should include the type, such
+   as::
+
+      .. cvar:: PyObject* PyClass_Type
+
+.. describe:: data
+
+   Describes global data in a module, including both variables and values used
+   as "defined constants."  Class and object attributes are not documented
+   using this environment.
+
+.. describe:: exception
+
+   Describes an exception class.  The signature can, but need not include
+   parentheses with constructor arguments.
+
+.. describe:: function
+
+   Describes a module-level function.  The signature should include the
+   parameters, enclosing optional parameters in brackets.  Default values can be
+   given if it enhances clarity.  For example::
+
+      .. function:: Timer.repeat([repeat=3[, number=1000000]])
+
+   Object methods are not documented using this directive. Bound object methods
+   placed in the module namespace as part of the public interface of the module
+   are documented using this, as they are equivalent to normal functions for
+   most purposes.
+
+   The description should include information about the parameters required and
+   how they are used (especially whether mutable objects passed as parameters
+   are modified), side effects, and possible exceptions.  A small example may be
+   provided.
+
+.. describe:: class
+
+   Describes a class.  The signature can include parentheses with parameters
+   which will be shown as the constructor arguments.
+
+.. describe:: attribute
+
+   Describes an object data attribute.  The description should include
+   information about the type of the data to be expected and whether it may be
+   changed directly.
+
+.. describe:: method
+
+   Describes an object method.  The parameters should not include the ``self``
+   parameter.  The description should include similar information to that
+   described for ``function``.
+
+.. describe:: opcode
+
+   Describes a Python :term:`bytecode` instruction.
+
+.. describe:: cmdoption
+
+   Describes a command line option or switch.  Option argument names should be
+   enclosed in angle brackets.  Example::
+
+      .. cmdoption:: -m <module>
+
+         Run a module as a script.
+
+.. describe:: envvar
+
+   Describes an environment variable that Python uses or defines.
+
+
+There is also a generic version of these directives:
+
+.. describe:: describe
+
+   This directive produces the same formatting as the specific ones explained
+   above but does not create index entries or cross-referencing targets.  It is
+   used, for example, to describe the directives in this document. Example::
+
+      .. describe:: opcode
+
+         Describes a Python bytecode instruction.
+
+
+Showing code examples
+---------------------
+
+Examples of Python source code or interactive sessions are represented using
+standard reST literal blocks.  They are started by a ``::`` at the end of the
+preceding paragraph and delimited by indentation.
+
+Representing an interactive session requires including the prompts and output
+along with the Python code.  No special markup is required for interactive
+sessions.  After the last line of input or output presented, there should not be
+an "unused" primary prompt; this is an example of what *not* to do::
+
+   >>> 1 + 1
+   2
+   >>>
+
+Syntax highlighting is handled in a smart way:
+
+* There is a "highlighting language" for each source file.  Per default,
+  this is ``'python'`` as the majority of files will have to highlight Python
+  snippets.
+
+* Within Python highlighting mode, interactive sessions are recognized
+  automatically and highlighted appropriately.
+
+* The highlighting language can be changed using the ``highlightlang``
+  directive, used as follows::
+
+     .. highlightlang:: c
+
+  This language is used until the next ``highlightlang`` directive is
+  encountered.
+
+* The valid values for the highlighting language are:
+
+  * ``python`` (the default)
+  * ``c``
+  * ``rest``
+  * ``none`` (no highlighting)
+
+* If highlighting with the current language fails, the block is not highlighted
+  in any way.
+
+Longer displays of verbatim text may be included by storing the example text in
+an external file containing only plain text.  The file may be included using the
+``literalinclude`` directive. [1]_ For example, to include the Python source file
+:file:`example.py`, use::
+
+   .. literalinclude:: example.py
+
+The file name is relative to the current file's path.  Documentation-specific
+include files should be placed in the ``Doc/includes`` subdirectory.
+
+
+Inline markup
+-------------
+
+As said before, Sphinx uses interpreted text roles to insert semantic markup in
+documents.
+
+Variable names are an exception, they should be marked simply with ``*var*``.
+
+For all other roles, you have to write ``:rolename:`content```.
+
+.. note::
+
+   For all cross-referencing roles, if you prefix the content with ``!``, no
+   reference/hyperlink will be created.
+
+The following roles refer to objects in modules and are possibly hyperlinked if
+a matching identifier is found:
+
+.. describe:: mod
+
+   The name of a module; a dotted name may be used.  This should also be used for
+   package names.
+
+.. describe:: func
+
+   The name of a Python function; dotted names may be used.  The role text
+   should not include trailing parentheses to enhance readability.  The
+   parentheses are stripped when searching for identifiers.
+
+.. describe:: data
+
+   The name of a module-level variable.
+
+.. describe:: const
+
+   The name of a "defined" constant.  This may be a C-language ``#define``
+   or a Python variable that is not intended to be changed.
+
+.. describe:: class
+
+   A class name; a dotted name may be used.
+
+.. describe:: meth
+
+   The name of a method of an object.  The role text should include the type
+   name and the method name.  A dotted name may be used.
+
+.. describe:: attr
+
+   The name of a data attribute of an object.
+
+.. describe:: exc
+
+   The name of an exception. A dotted name may be used.
+
+The name enclosed in this markup can include a module name and/or a class name.
+For example, ``:func:`filter``` could refer to a function named ``filter`` in
+the current module, or the built-in function of that name.  In contrast,
+``:func:`foo.filter``` clearly refers to the ``filter`` function in the ``foo``
+module.
+
+Normally, names in these roles are searched first without any further
+qualification, then with the current module name prepended, then with the
+current module and class name (if any) prepended.  If you prefix the name with a
+dot, this order is reversed.  For example, in the documentation of the
+:mod:`codecs` module, ``:func:`open``` always refers to the built-in function,
+while ``:func:`.open``` refers to :func:`codecs.open`.
+
+A similar heuristic is used to determine whether the name is an attribute of
+the currently documented class.
+
+The following roles create cross-references to C-language constructs if they
+are defined in the API documentation:
+
+.. describe:: cdata
+
+   The name of a C-language variable.
+
+.. describe:: cfunc
+
+   The name of a C-language function. Should include trailing parentheses.
+
+.. describe:: cmacro
+
+   The name of a "simple" C macro, as defined above.
+
+.. describe:: ctype
+
+   The name of a C-language type.
+
+
+The following role does possibly create a cross-reference, but does not refer
+to objects:
+
+.. describe:: token
+
+   The name of a grammar token (used in the reference manual to create links
+   between production displays).
+
+
+The following role creates a cross-reference to the term in the glossary:
+
+.. describe:: term
+
+   Reference to a term in the glossary.  The glossary is created using the
+   ``glossary`` directive containing a definition list with terms and
+   definitions.  It does not have to be in the same file as the ``term``
+   markup, in fact, by default the Python docs have one global glossary
+   in the ``glossary.rst`` file.
+
+   If you use a term that's not explained in a glossary, you'll get a warning
+   during build.
+
+---------
+
+The following roles don't do anything special except formatting the text
+in a different style:
+
+.. describe:: command
+
+   The name of an OS-level command, such as ``rm``.
+
+.. describe:: dfn
+
+   Mark the defining instance of a term in the text.  (No index entries are
+   generated.)
+
+.. describe:: envvar
+
+   An environment variable.  Index entries are generated.
+
+.. describe:: file
+
+   The name of a file or directory.  Within the contents, you can use curly
+   braces to indicate a "variable" part, for example::
+
+      ... is installed in :file:`/usr/lib/python2.{x}/site-packages` ...
+
+   In the built documentation, the ``x`` will be displayed differently to
+   indicate that it is to be replaced by the Python minor version.
+
+.. describe:: guilabel
+
+   Labels presented as part of an interactive user interface should be marked
+   using ``guilabel``.  This includes labels from text-based interfaces such as
+   those created using :mod:`curses` or other text-based libraries.  Any label
+   used in the interface should be marked with this role, including button
+   labels, window titles, field names, menu and menu selection names, and even
+   values in selection lists.
+
+.. describe:: kbd
+
+   Mark a sequence of keystrokes.  What form the key sequence takes may depend
+   on platform- or application-specific conventions.  When there are no relevant
+   conventions, the names of modifier keys should be spelled out, to improve
+   accessibility for new users and non-native speakers.  For example, an
+   *xemacs* key sequence may be marked like ``:kbd:`C-x C-f```, but without
+   reference to a specific application or platform, the same sequence should be
+   marked as ``:kbd:`Control-x Control-f```.
+
+.. describe:: keyword
+
+   The name of a keyword in Python.
+
+.. describe:: mailheader
+
+   The name of an RFC 822-style mail header.  This markup does not imply that
+   the header is being used in an email message, but can be used to refer to any
+   header of the same "style."  This is also used for headers defined by the
+   various MIME specifications.  The header name should be entered in the same
+   way it would normally be found in practice, with the camel-casing conventions
+   being preferred where there is more than one common usage. For example:
+   ``:mailheader:`Content-Type```.
+
+.. describe:: makevar
+
+   The name of a :command:`make` variable.
+
+.. describe:: manpage
+
+   A reference to a Unix manual page including the section,
+   e.g. ``:manpage:`ls(1)```.
+
+.. describe:: menuselection
+
+   Menu selections should be marked using the ``menuselection`` role.  This is
+   used to mark a complete sequence of menu selections, including selecting
+   submenus and choosing a specific operation, or any subsequence of such a
+   sequence.  The names of individual selections should be separated by
+   ``-->``.
+
+   For example, to mark the selection "Start > Programs", use this markup::
+
+      :menuselection:`Start --> Programs`
+
+   When including a selection that includes some trailing indicator, such as the
+   ellipsis some operating systems use to indicate that the command opens a
+   dialog, the indicator should be omitted from the selection name.
+
+.. describe:: mimetype
+
+   The name of a MIME type, or a component of a MIME type (the major or minor
+   portion, taken alone).
+
+.. describe:: newsgroup
+
+   The name of a Usenet newsgroup.
+
+.. describe:: option
+
+   A command-line option to an executable program.  The leading hyphen(s) must
+   be included.
+
+.. describe:: program
+
+   The name of an executable program.  This may differ from the file name for
+   the executable for some platforms.  In particular, the ``.exe`` (or other)
+   extension should be omitted for Windows programs.
+
+.. describe:: regexp
+
+   A regular expression. Quotes should not be included.
+
+.. describe:: samp
+
+   A piece of literal text, such as code.  Within the contents, you can use
+   curly braces to indicate a "variable" part, as in ``:file:``.
+
+   If you don't need the "variable part" indication, use the standard
+   ````code```` instead.   
+
+.. describe:: var
+
+   A Python or C variable or parameter name.
+
+
+The following roles generate external links:
+
+.. describe:: pep
+
+   A reference to a Python Enhancement Proposal.  This generates appropriate
+   index entries. The text "PEP *number*\ " is generated; in the HTML output,
+   this text is a hyperlink to an online copy of the specified PEP.
+
+.. describe:: rfc
+
+   A reference to an Internet Request for Comments.  This generates appropriate
+   index entries. The text "RFC *number*\ " is generated; in the HTML output,
+   this text is a hyperlink to an online copy of the specified RFC.
+
+
+Note that there are no special roles for including hyperlinks as you can use
+the standard reST markup for that purpose.
+
+
+.. _doc-ref-role:
+
+Cross-linking markup
+--------------------
+
+To support cross-referencing to arbitrary sections in the documentation, the
+standard reST labels are "abused" a bit: Every label must precede a section
+title; and every label name must be unique throughout the entire documentation
+source.
+
+You can then reference to these sections using the ``:ref:`label-name``` role.
+
+Example::
+
+   .. _my-reference-label:
+
+   Section to cross-reference
+   --------------------------
+
+   This is the text of the section.
+
+   It refers to the section itself, see :ref:`my-reference-label`.
+
+The ``:ref:`` invocation is replaced with the section title.
+
+
+Paragraph-level markup
+----------------------
+
+These directives create short paragraphs and can be used inside information
+units as well as normal text:
+
+.. describe:: note
+
+   An especially important bit of information about an API that a user should be
+   aware of when using whatever bit of API the note pertains to.  The content of
+   the directive should be written in complete sentences and include all
+   appropriate punctuation.
+
+   Example::
+
+      .. note::
+
+         This function is not suitable for sending spam e-mails.
+
+.. describe:: warning
+
+   An important bit of information about an API that a user should be very aware
+   of when using whatever bit of API the warning pertains to.  The content of
+   the directive should be written in complete sentences and include all
+   appropriate punctuation. This differs from ``note`` in that it is recommended
+   over ``note`` for information regarding security.
+
+.. describe:: versionadded
+
+   This directive documents the version of Python which added the described
+   feature to the library or C API. When this applies to an entire module, it
+   should be placed at the top of the module section before any prose.
+
+   The first argument must be given and is the version in question; you can add
+   a second argument consisting of a *brief* explanation of the change.
+
+   Example::
+
+      .. versionadded:: 2.5
+         The `spam` parameter.
+
+   Note that there must be no blank line between the directive head and the
+   explanation; this is to make these blocks visually continuous in the markup.
+
+.. describe:: versionchanged
+
+   Similar to ``versionadded``, but describes when and what changed in the named
+   feature in some way (new parameters, changed side effects, etc.).
+
+--------------
+
+.. describe:: seealso
+
+   Many sections include a list of references to module documentation or
+   external documents.  These lists are created using the ``seealso`` directive.
+
+   The ``seealso`` directive is typically placed in a section just before any
+   sub-sections.  For the HTML output, it is shown boxed off from the main flow
+   of the text.
+
+   The content of the ``seealso`` directive should be a reST definition list.
+   Example::
+
+      .. seealso::
+
+         Module :mod:`zipfile`
+            Documentation of the :mod:`zipfile` standard module.
+
+         `GNU tar manual, Basic Tar Format <http://link>`_
+            Documentation for tar archive files, including GNU tar extensions.
+
+.. describe:: rubric
+
+   This directive creates a paragraph heading that is not used to create a
+   table of contents node.  It is currently used for the "Footnotes" caption.
+
+.. describe:: centered
+
+   This directive creates a centered boldfaced paragraph.  Use it as follows::
+
+      .. centered::
+
+         Paragraph contents.
+
+
+Table-of-contents markup
+------------------------
+
+Since reST does not have facilities to interconnect several documents, or split
+documents into multiple output files, Sphinx uses a custom directive to add
+relations between the single files the documentation is made of, as well as
+tables of contents.  The ``toctree`` directive is the central element.
+
+.. describe:: toctree
+
+   This directive inserts a "TOC tree" at the current location, using the
+   individual TOCs (including "sub-TOC trees") of the files given in the
+   directive body.  A numeric ``maxdepth`` option may be given to indicate the
+   depth of the tree; by default, all levels are included.
+
+   Consider this example (taken from the library reference index)::
+
+      .. toctree::
+         :maxdepth: 2
+
+         intro.rst
+         strings.rst
+         datatypes.rst
+         numeric.rst
+         (many more files listed here)
+
+   This accomplishes two things:
+
+   * Tables of contents from all those files are inserted, with a maximum depth
+     of two, that means one nested heading.  ``toctree`` directives in those
+     files are also taken into account.
+   * Sphinx knows that the relative order of the files ``intro.rst``,
+     ``strings.rst`` and so forth, and it knows that they are children of the
+     shown file, the library index.  From this information it generates "next
+     chapter", "previous chapter" and "parent chapter" links.
+
+   In the end, all files included in the build process must occur in one
+   ``toctree`` directive; Sphinx will emit a warning if it finds a file that is
+   not included, because that means that this file will not be reachable through
+   standard navigation.
+
+   The special file ``contents.rst`` at the root of the source directory is the
+   "root" of the TOC tree hierarchy; from it the "Contents" page is generated.
+
+
+Index-generating markup
+-----------------------
+
+Sphinx automatically creates index entries from all information units (like
+functions, classes or attributes) like discussed before.
+
+However, there is also an explicit directive available, to make the index more
+comprehensive and enable index entries in documents where information is not
+mainly contained in information units, such as the language reference.
+
+The directive is ``index`` and contains one or more index entries.  Each entry
+consists of a type and a value, separated by a colon.
+
+For example::
+
+   .. index::
+      single: execution; context
+      module: __main__
+      module: sys
+      triple: module; search; path
+
+This directive contains five entries, which will be converted to entries in the
+generated index which link to the exact location of the index statement (or, in
+case of offline media, the corresponding page number).
+
+The possible entry types are:
+
+single
+   Creates a single index entry.  Can be made a subentry by separating the
+   subentry text with a semicolon (this notation is also used below to describe
+   what entries are created).
+pair
+   ``pair: loop; statement`` is a shortcut that creates two index entries,
+   namely ``loop; statement`` and ``statement; loop``.
+triple
+   Likewise, ``triple: module; search; path`` is a shortcut that creates three
+   index entries, which are ``module; search path``, ``search; path, module`` and
+   ``path; module search``.
+module, keyword, operator, object, exception, statement, builtin
+   These all create two index entries.  For example, ``module: hashlib`` creates
+   the entries ``module; hashlib`` and ``hashlib; module``.
+
+For index directives containing only "single" entries, there is a shorthand
+notation::
+
+   .. index:: BNF, grammar, syntax, notation
+
+This creates four index entries.
+
+
+Grammar production displays
+---------------------------
+
+Special markup is available for displaying the productions of a formal grammar.
+The markup is simple and does not attempt to model all aspects of BNF (or any
+derived forms), but provides enough to allow context-free grammars to be
+displayed in a way that causes uses of a symbol to be rendered as hyperlinks to
+the definition of the symbol.  There is this directive:
+
+.. describe:: productionlist
+
+   This directive is used to enclose a group of productions.  Each production is
+   given on a single line and consists of a name, separated by a colon from the
+   following definition.  If the definition spans multiple lines, each
+   continuation line must begin with a colon placed at the same column as in the
+   first line.
+
+   Blank lines are not allowed within ``productionlist`` directive arguments.
+
+   The definition can contain token names which are marked as interpreted text
+   (e.g. ``sum ::= `integer` "+" `integer```) -- this generates cross-references
+   to the productions of these tokens.
+
+   Note that no further reST parsing is done in the production, so that you
+   don't have to escape ``*`` or ``|`` characters.
+
+
+.. XXX describe optional first parameter 
+
+The following is an example taken from the Python Reference Manual::
+
+   .. productionlist::
+      try_stmt: try1_stmt | try2_stmt
+      try1_stmt: "try" ":" `suite`
+               : ("except" [`expression` ["," `target`]] ":" `suite`)+
+               : ["else" ":" `suite`]
+               : ["finally" ":" `suite`]
+      try2_stmt: "try" ":" `suite`
+               : "finally" ":" `suite`
+
+
+Substitutions
+-------------
+
+The documentation system provides three substitutions that are defined by default.
+They are set in the build configuration file, see :ref:`doc-build-config`.
+
+.. describe:: |release|
+
+   Replaced by the Python release the documentation refers to.  This is the full
+   version string including alpha/beta/release candidate tags, e.g. ``2.5.2b3``.
+
+.. describe:: |version|
+
+   Replaced by the Python version the documentation refers to. This consists
+   only of the major and minor version parts, e.g. ``2.5``, even for version
+   2.5.1.
+
+.. describe:: |today|
+
+   Replaced by either today's date, or the date set in the build configuration
+   file.  Normally has the format ``April 14, 2007``.
+
+
+.. rubric:: Footnotes
+
+.. [1] There is a standard ``.. include`` directive, but it raises errors if the
+       file is not found.  This one only emits a warning.