Make TextIOWrapper's documentation clearer by copying the newline argument's description from open().

Doc/library/io.rst

@@ -754,14 +754,22 @@ Text I/O
    sequences) can be used.  Any other error handling name that has been
    registered with :func:`codecs.register_error` is also valid.
 
-   *newline* can be ``None``, ``''``, ``'\n'``, ``'\r'``, or ``'\r\n'``.  It
-   controls the handling of line endings.  If it is ``None``, universal newlines
-   is enabled.  With this enabled, on input, the lines endings ``'\n'``,
-   ``'\r'``, or ``'\r\n'`` are translated to ``'\n'`` before being returned to
-   the caller.  Conversely, on output, ``'\n'`` is translated to the system
-   default line separator, :data:`os.linesep`.  If *newline* is any other of its
-   legal values, that newline becomes the newline when the file is read and it
-   is returned untranslated.  On output, ``'\n'`` is converted to the *newline*.
+   *newline* controls how line endings are handled.  It can be ``None``,
+   ``''``, ``'\n'``, ``'\r'``, and ``'\r\n'``.  It works as follows:
+
+   * On input, if *newline* is ``None``, universal newlines mode is enabled.
+     Lines in the input can end in ``'\n'``, ``'\r'``, or ``'\r\n'``, and these
+     are translated into ``'\n'`` before being returned to the caller.  If it is
+     ``''``, universal newline mode is enabled, but line endings are returned to
+     the caller untranslated.  If it has any of the other legal values, input
+     lines are only terminated by the given string, and the line ending is
+     returned to the caller untranslated.
+
+   * On output, if *newline* is ``None``, any ``'\n'`` characters written are
+     translated to the system default line separator, :data:`os.linesep`.  If
+     *newline* is ``''``, no translation takes place.  If *newline* is any of
+     the other legal values, any ``'\n'`` characters written are translated to
+     the given string.
 
    If *line_buffering* is ``True``, :meth:`flush` is implied when a call to
    write contains a newline character.

Modules/_io/textio.c

@@ -622,15 +622,22 @@ PyDoc_STRVAR(textiowrapper_doc,
     "errors determines the strictness of encoding and decoding (see the\n"
     "codecs.register) and defaults to \"strict\".\n"
     "\n"
-    "newline can be None, '', '\\n', '\\r', or '\\r\\n'.  It controls the\n"
-    "handling of line endings. If it is None, universal newlines is\n"
-    "enabled.  With this enabled, on input, the lines endings '\\n', '\\r',\n"
-    "or '\\r\\n' are translated to '\\n' before being returned to the\n"
-    "caller. Conversely, on output, '\\n' is translated to the system\n"
-    "default line separator, os.linesep. If newline is any other of its\n"
-    "legal values, that newline becomes the newline when the file is read\n"
-    "and it is returned untranslated. On output, '\\n' is converted to the\n"
-    "newline.\n"
+    "newline controls how line endings are handled. It can be None, '',\n"
+    "'\\n', '\\r', and '\\r\\n'.  It works as follows:\n"
+    "\n"
+    "* On input, if newline is None, universal newlines mode is\n"
+    "  enabled. Lines in the input can end in '\\n', '\\r', or '\\r\\n', and\n"
+    "  these are translated into '\\n' before being returned to the\n"
+    "  caller. If it is '', universal newline mode is enabled, but line\n"
+    "  endings are returned to the caller untranslated. If it has any of\n"
+    "  the other legal values, input lines are only terminated by the given\n"
+    "  string, and the line ending is returned to the caller untranslated.\n"
+    "\n"
+    "* On output, if newline is None, any '\\n' characters written are\n"
+    "  translated to the system default line separator, os.linesep. If\n"
+    "  newline is '', no translation takes place. If newline is any of the\n"
+    "  other legal values, any '\\n' characters written are translated to\n"
+    "  the given string.\n"
     "\n"
     "If line_buffering is True, a call to flush is implied when a call to\n"
     "write contains a newline character."