Describe 'surrogateescape' in the documentation.

Also, improve some docstring descriptions of the 'errors' parameter.

Closes #14015.

Doc/library/codecs.rst

@@ -78,7 +78,11 @@ It defines the following functions:
      reference (for encoding only)
    * ``'backslashreplace'``: replace with backslashed escape sequences (for
      encoding only)
-   * ``'surrogateescape'``: replace with surrogate U+DCxx, see :pep:`383`
+   * ``'surrogateescape'``: on decoding, replace with code points in the Unicode
+     Private Use Area ranging from U+DC80 to U+DCFF.  These private code
+     points will then be turned back into the same bytes when the
+     ``surrogateescape`` error handler is used when encoding the data.
+     (See :pep:`383` for more.)
 
    as well as any other error handling name defined via :func:`register_error`.
 

Doc/library/functions.rst

@@ -895,16 +895,36 @@ are always available.  They are listed here in alphabetical order.
    the list of supported encodings.
 
    *errors* is an optional string that specifies how encoding and decoding
-   errors are to be handled--this cannot be used in binary mode.  Pass
-   ``'strict'`` to raise a :exc:`ValueError` exception if there is an encoding
-   error (the default of ``None`` has the same effect), or pass ``'ignore'`` to
-   ignore errors.  (Note that ignoring encoding errors can lead to data loss.)
-   ``'replace'`` causes a replacement marker (such as ``'?'``) to be inserted
-   where there is malformed data.  When writing, ``'xmlcharrefreplace'``
-   (replace with the appropriate XML character reference) or
-   ``'backslashreplace'`` (replace with backslashed escape sequences) can be
-   used.  Any other error handling name that has been registered with
-   :func:`codecs.register_error` is also valid.
+   errors are to be handled--this cannot be used in binary mode.
+   A variety of standard error handlers are available, though any
+   error handling name that has been registered with
+   :func:`codecs.register_error` is also valid.  The standard names
+   are:
+
+   * ``'strict'`` to raise a :exc:`ValueError` exception if there is
+     an encoding error.  The default value of ``None`` has the same
+     effect.
+
+   * ``'ignore'`` ignores errors.  Note that ignoring encoding errors
+     can lead to data loss.
+
+   * ``'replace'`` causes a replacement marker (such as ``'?'``) to be inserted
+     where there is malformed data.
+
+   * ``'surrogateescape'`` will represent any incorrect bytes as code
+     points in the Unicode Private Use Area ranging from U+DC80 to
+     U+DCFF.  These private code points will then be turned back into
+     the same bytes when the ``surrogateescape`` error handler is used
+     when writing data.  This is useful for processing files in an
+     unknown encoding.
+
+   * ``'xmlcharrefreplace'`` is only supported when writing to a file.
+     Characters not supported by the encoding are replaced with the
+     appropriate XML character reference ``&#nnn;``.
+
+   * ``'backslashreplace'`` (also only supported when writing)
+     replaces unsupported characters with Python's backslashed escape
+     sequences.
 
    .. index::
       single: universal newlines; open() built-in function

Lib/codecs.py

@@ -105,6 +105,7 @@ class Codec:
                     Python will use the official U+FFFD REPLACEMENT
                     CHARACTER for the builtin Unicode codecs on
                     decoding and '?' on encoding.
+         'surrogateescape' - replace with private codepoints U+DCnn.
          'xmlcharrefreplace' - Replace with the appropriate XML
                                character reference (only for encoding).
          'backslashreplace'  - Replace with backslashed escape sequences

Modules/_io/_iomodule.c

@@ -168,8 +168,8 @@ PyDoc_STRVAR(open_doc,
 "'strict' to raise a ValueError exception if there is an encoding error\n"
 "(the default of None has the same effect), or pass 'ignore' to ignore\n"
 "errors. (Note that ignoring encoding errors can lead to data loss.)\n"
-"See the documentation for codecs.register for a list of the permitted\n"
-"encoding error strings.\n"
+"See the documentation for codecs.register or run 'help(codecs.Codec)'\n"
+"for a list of the permitted encoding error strings.\n"
 "\n"
 "newline controls how universal newlines works (it only applies to text\n"
 "mode). It can be None, '', '\\n', '\\r', and '\\r\\n'.  It works as\n"

Modules/_io/textio.c

@@ -642,8 +642,9 @@ PyDoc_STRVAR(textiowrapper_doc,
     "encoding gives the name of the encoding that the stream will be\n"
     "decoded or encoded with. It defaults to locale.getpreferredencoding(False).\n"
     "\n"
-    "errors determines the strictness of encoding and decoding (see the\n"
-    "codecs.register) and defaults to \"strict\".\n"
+    "errors determines the strictness of encoding and decoding (see\n"
+    "help(codecs.Codec) or the documentation for codecs.register) and\n"
+    "defaults to \"strict\".\n"
     "\n"
     "newline controls how line endings are handled. It can be None, '',\n"
     "'\\n', '\\r', and '\\r\\n'.  It works as follows:\n"