Index: Doc/library/os.rst
===================================================================
--- Doc/library/os.rst	(revision 80077)
+++ Doc/library/os.rst	(working copy)
@@ -655,14 +655,19 @@
 
 .. function:: open(file, flags[, mode])
 
-   Open the file *file* and set various flags according to *flags* and possibly its
-   mode according to *mode*. The default *mode* is ``0777`` (octal), and the
-   current umask value is first masked out.  Return the file descriptor for the
-   newly opened file. Availability: Unix, Windows.
+   Open the file *file* using low level system call and return its descriptor
+   that can be used with other :ref:`os-fd-ops`. *flags* specify how the file
+   should be opened with constants defined in :ref:`os-open-flags` section below.
+   Optional *mode* parameter contains unix-like permissions for newly created
+   file and has value of ``0777`` (octal) by default. Current umask value is
+   first masked out.
+   Availability: Unix, Windows.
 
-   For a description of the flag and mode values, see the C run-time documentation;
-   flag constants (like :const:`O_RDONLY` and :const:`O_WRONLY`) are defined in
-   this module too (see :ref:`open-constants`).
+   .. warning::
+ 
+      On Windows this function opens file in text mode by default, while on Unix
+      all files opened as binary. To preserve crossplatform behavior add
+      :const:`O_BINARY` flag while on Windows.
 
    .. note::
 
@@ -736,15 +741,15 @@
       :meth:`~file.write` method.
 
 
-.. _open-constants:
+.. _os-open-flags:
 
-``open()`` flag constants
-~~~~~~~~~~~~~~~~~~~~~~~~~
+``os.open`` flags
+^^^^^^^^^^^^^^^^^
 
-The following constants are options for the *flags* parameter to the
-:func:`~os.open` function.  They can be combined using the bitwise OR operator
-``|``.  Some of them are not available on all platforms.  For descriptions of
-their availability and use, consult the :manpage:`open(2)` manual page on Unix
+:func:`os.open` function understands the following *flag* constants that can be combined
+using the bitwise OR operator ``|``.  Some of them are not available on all platforms.
+For descriptions and availability, consult the C run-time documentation: the
+:manpage:`open(2)` manual page on Unix
 or `the MSDN <http://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windows.