#10439: document PyCodec C APIs.

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+.. _codec-registry:
+
+Codec registry and support functions
+====================================
+
+.. c:function:: int PyCodec_Register(PyObject *search_function)
+
+   Register a new codec search function.
+
+   As side effect, this tries to load the :mod:`encodings` package, if not yet
+   done, to make sure that it is always first in the list of search functions.
+
+.. c:function:: int PyCodec_KnownEncoding(const char *encoding)
+
+   Return ``1`` or ``0`` depending on whether there is a registered codec for
+   the given *encoding*.
+
+.. c:function:: PyObject* PyCodec_Encode(PyObject *object, const char *encoding, const char *errors)
+
+   Generic codec based encoding API.
+
+   *object* is passed through the encoder function found for the given
+   *encoding* using the error handling method defined by *errors*.  *errors* may
+   be *NULL* to use the default method defined for the codec.  Raises a
+   :exc:`LookupError` if no encoder can be found.
+
+.. c:function:: PyObject* PyCodec_Decode(PyObject *object, const char *encoding, const char *errors)
+
+   Generic codec based decoding API.
+
+   *object* is passed through the decoder function found for the given
+   *encoding* using the error handling method defined by *errors*.  *errors* may
+   be *NULL* to use the default method defined for the codec.  Raises a
+   :exc:`LookupError` if no encoder can be found.
+
+
+Codec lookup API
+----------------
+
+In the following functions, the *encoding* string is looked up converted to all
+lower-case characters, which makes encodings looked up through this mechanism
+effectively case-insensitive.  If no codec is found, a :exc:`KeyError` is set
+and *NULL* returned.
+
+.. c:function:: PyObject* PyCodec_Encoder(const char *encoding)
+
+   Get an encoder function for the given *encoding*.
+
+.. c:function:: PyObject* PyCodec_Decoder(const char *encoding)
+
+   Get a decoder function for the given *encoding*.
+
+.. c:function:: PyObject* PyCodec_IncrementalEncoder(const char *encoding, const char *errors)
+
+   Get an :class:`IncrementalEncoder` object for the given *encoding*.
+
+.. c:function:: PyObject* PyCodec_IncrementalDecoder(const char *encoding, const char *errors)
+
+   Get an :class:`IncrementalDecoder` object for the given *encoding*.
+
+.. c:function:: PyObject* PyCodec_StreamReader(const char *encoding, PyObject *stream, const char *errors)
+
+   Get a :class:`StreamReader` factory function for the given *encoding*.
+
+.. c:function:: PyObject* PyCodec_StreamWriter(const char *encoding, PyObject *stream, const char *errors)
+
+   Get a :class:`StreamWriter` factory function for the given *encoding*.
+
+
+Registry API for Unicode encoding error handlers
+------------------------------------------------
+
+.. c:function:: int PyCodec_RegisterError(const char *name, PyObject *error)
+
+   Register the error handling callback function *error* under the given *name*.
+   This callback function will be called by a codec when it encounters
+   unencodable characters/undecodable bytes and *name* is specified as the error
+   parameter in the call to the encode/decode function.
+
+   The callback gets a single argument, an instance of
+   :exc:`UnicodeEncodeError`, :exc:`UnicodeDecodeError` or
+   :exc:`UnicodeTranslateError` that holds information about the problematic
+   sequence of characters or bytes and their offset in the original string.  The
+   callback must either raise the given exception, or return a two-item tuple
+   containing the replacement for the problematic sequence, and an integer
+   giving the offset in the original string at which encoding/decoding should be
+   resumed.
+
+   .. XXX once they are documented, link to PyUnicode*Error access functions
+      to show how to get at the exception properties
+
+   Return ``0`` on success, ``-1`` on error.
+
+.. c:function:: PyObject* PyCodec_LookupError(const char *name)
+
+   Lookup the error handling callback function registered under *name*.  As a
+   special case *NULL* can be passed, in which case the error handling callback
+   for "strict" will be returned.
+
+.. c:function:: PyObject* PyCodec_StrictErrors(PyObject *exc)
+
+   Raise *exc* as an exception.
+
+.. c:function:: PyObject* PyCodec_IgnoreErrors(PyObject *exc)
+
+   Ignore the unicode error, skipping the faulty input.
+
+.. c:function:: PyObject* PyCodec_ReplaceErrors(PyObject *exc)
+
+   Replace the unicode encode error with ``?`` or ``U+FFFD``.
+
+.. c:function:: PyObject* PyCodec_XMLCharRefReplaceErrors(PyObject *exc)
+
+   Replace the unicode encode error with XML character references.
+
+.. c:function:: PyObject* PyCodec_BackslashReplaceErrors(PyObject *exc)
+
+   Replace the unicode encode error with backslash escapes (``\x``, ``\u`` and
+   ``\U``).
+