os module doc, File Descriptor Operations, at end.

Suggestions:

1. Replace
"The following data items are available for use in constructing the
flags parameter to the open() function."
with
"The following data items are options for the flag argument to the
open() function. These can be combined using the bitwise OR operator |."
(and remove the redundant text from the block headings -- see below).

2. In the next sentence, replace 'will not be' with 'are not'.

3. The next sentence ends with 'consult open(2).' I presume this refers
to unix manual section on the open system call.  This is cryptic and
useless to many Windows users.  Where are descriptions for flags valid
on Windows?

4. Block captions: remove repeated text and move availability note above
rather than below the block. 'Available on Unix and Windows', 'Available
on Unix only', 'Available on Windows only', 'Gnu extensions....'.

5. The items in the fifth block are *not* open() options.  The caption
should instead be an un-indented introductory sentence before the block.
"The following data items are parameters to the lseek() function. ..."

Fixed in r67556.  If a Windows guy can give me more specific directions
where to find the equivalent options, I'll put it in.

http://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx is the
documentation for the open() function of the Microsoft C Runtime, but I
don't know how permanent this link will be.

Added link in r67574.