diff --git a/Doc/library/codecs.rst b/Doc/library/codecs.rst
index ab578ea..3f1a5fe 100644
--- a/Doc/library/codecs.rst
+++ b/Doc/library/codecs.rst
@@ -322,6 +322,8 @@
 | ``'backslashreplace'``  | Replace with backslashed escape sequences     |
 |                         | (only for encoding).                          |
 +-------------------------+-----------------------------------------------+
+| ``'utf8b'``             | Replace byte with surrogate U+DCxx.           |
++-------------------------+-----------------------------------------------+
 
 In addition, the following error handlers are specific to a single codec:
 
@@ -333,7 +335,7 @@
 +------------------+---------+--------------------------------------------+
 
 .. versionadded:: 3.1
-   The ``'surrogates'`` error handler.
+   The ``'utf8b'`` and ``'surrogates'`` error handlers.
 
 The set of allowed values can be extended via :meth:`register_error`.
 
diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index c686baf..83f5ee9 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -51,6 +51,30 @@
    ``'ce'``, ``'java'``.
 
 
+.. _os-filenames:
+
+File Names, Command Line Arguments, and Environment Variables
+-------------------------------------------------------------
+
+In Python, file names, command line arguments, and environment
+variables are represented using the string type. On some systems,
+decoding these strings to and from bytes is necessary before passing
+them to the operating system. Python uses the file system encoding to
+perform this conversion (see :func:`sys.getfilesystemencoding`).
+
+.. versionchanged:: 3.1
+   On some systems, conversion using the file system encoding may
+   fail. In this case, Python uses the ``utf8b`` encoding error
+   handler, which means that undecodable bytes are replaced by a
+   Unicode character U+DCxx on decoding, and these are again
+   translated to the original byte on encoding.
+
+
+The file system encoding must guarantee to successfully decode all
+bytes below 128. If the file system encoding fails to provide this
+guarantee, API functions may raise UnicodeErrors.
+
+
 .. _os-procinfo:
 
 Process Parameters
@@ -688,12 +712,8 @@
 
 .. function:: getcwd()
 
-   Return a string representing the current working directory.  On Unix
-   platforms, this function may raise :exc:`UnicodeDecodeError` if the name of
-   the current directory is not decodable in the file system encoding.  Use
-   :func:`getcwdb` if you need the call to never fail. Availability: Unix,
-   Windows.
-
+   Return a string representing the current working directory.
+   Availability: Unix, Windows.
 
 .. function:: getcwdb()
 
@@ -800,10 +820,8 @@
    entries ``'.'`` and ``'..'`` even if they are present in the directory.
    Availability: Unix, Windows.
 
-   This function can be called with a bytes or string argument.  In the bytes
-   case, all filenames will be listed as returned by the underlying API.  In the
-   string case, filenames will be decoded using the file system encoding, and
-   skipped if a decoding error occurs.
+   This function can be called with a bytes or string argument, and returns
+   filenames of the same datatype.
 
 
 .. function:: lstat(path)