Differences added in initial PR:
* threading.activeCount()`` returns 2 instead of 1;
* run user code in separate process;
* user-created subprocesses do not inherit sys.stdxxx objects;
  must run IDLE from console for such to have i/o connection;
* Shell ignores anything after first statement in pasted code.

Dependencies
Issue #23220 added the "IDLE-console differences" subsection to IDLE doc.
Discussing 'Shell not a terminal' left for another patch.

Issue 33000 is about finite versus infinite buffer.

Or should any of these be in new Shell subsection?

Just a comment on usage, for what it's worth: I don't know how common the term "console" is on modern Windows systems, but I think the term has a very different meaning on Unix and macOS.  In those environments, if used at all, a "console" *might* refer to a window that provides access to admin functions.  A normal (non-admin) user would not use or even be familiar with the term "console" in this context.  A more familiar term would be a "terminal window" or "shell window" or some such.  But I'm not sure I even understand totally what is meant by "console" here; it's just sounds foreign :)

By 'console' I mean the text-interface window that Python normally runs in, whether in batch or interactive mode, whether started directly from an icon or menu or file listing or indirectly by entering 'python' in a shell program running in the console.  (On Windows, there is only the one text UI program.)

On Windows, 'console' is the proper term (as Eryk Sun has taken pains to point out).  "Command Prompt' (cmd.exe)*, 'PowerShell' (???.exe) and Python (python.exe, when run directly without using either command-line program) all use the same console as their UI.  In all cases, the app interacts with users through a console window just as IDLE interacts with users through tk windows.

*Naive Windows users sometimes call a console window a Command Prompt window or every a Dos Prompt window, even when Python is running in such a window without cmd.exe.

In all cases, clicking the icon in the upper left corner displays the console menu.  Selecting 'Properties' displays the console properties dialog.  Selecting the 'Options' tab displays an option to use the 'legacy console' rather than the 'new console'.

I appreciate being informed that the naked term does not work for other systems.  Would it be sufficient to define 'console' as the text interface window that Python normally runs in, which might instead be caller a terminal, terminal window, or shell window?  I would rather not have to use 'console or terminal' everywhere.

'IDLE - console differences' is about differences in execution result and output display* when running Python code through IDLE (using tk) instead of Python in its standard running-in-a-console mode.  Do you have a better idea of how to reduce this to a few words?  How about 'IDLE - console Python differences', with an explanation of 'console Python'?  ('terminal Python' reminds me of dead parrots ;-)

(Since I opened this issue, I realized that the pasting difference is a code preparation difference that belongs elsewhere.)

Thanks for the explanation.  That's what I thought you meant but it's good to make sure.  I'm not sure what the best solution is and others might have a different opinion.  It might be good to solicit some feedback from a wider audience of users who do not have Windows experience.

I thought of 'IDLE versus standard Python', or 'default Python', but the contrast is not correct, as IDLE uses the same Python.  The intended contrast is between the result of different methods of running Python code with a particular Python binary.  'How IDLE modifies execution results' is correct, but I don't especially like it.

I can ask for other opinions on idledev and python-list.  In the meanwhile, I have a patch nearly ready, and want to move on to the dependency issues that will edit the same section.  So while waiting for opinions, I want to merge a version of what I have, but leave this open pending a final decision on the title and terminology.

New changeset 5e7909032491cef17754a3208872655fe350e9be by Terry Jan Reedy in branch 'master':
 bpo-35099: Improve the doc about IDLE running user code. (#10350)
https://github.com/python/cpython/commit/5e7909032491cef17754a3208872655fe350e9be

New changeset a437c285fa4f21720802e7a91770b2281d576554 by Miss Islington (bot) in branch '3.7':
bpo-35099: Improve the doc about IDLE running user code. (GH-10350)
https://github.com/python/cpython/commit/a437c285fa4f21720802e7a91770b2281d576554

New changeset 927a113ae2be33a9dd929569930f28948aa5c965 by Miss Islington (bot) in branch '3.6':
bpo-35099: Improve the doc about IDLE running user code. (GH-10350)
https://github.com/python/cpython/commit/927a113ae2be33a9dd929569930f28948aa5c965

I either removed or augmented occurrences of 'console' in the renamed section.

New changeset f1d3efc2fba704692d539acc3cb0376a1dd9d98f by Terry Jan Reedy in branch 'master':
bpo-35099: Update idlelib/help.html (#10353)
https://github.com/python/cpython/commit/f1d3efc2fba704692d539acc3cb0376a1dd9d98f

New changeset 4a46295a95bc2e7a93bcf0ce4cdaeeeb48729069 by Miss Islington (bot) in branch '3.7':
bpo-35099: Update idlelib/help.html (GH-10353)
https://github.com/python/cpython/commit/4a46295a95bc2e7a93bcf0ce4cdaeeeb48729069

New changeset 54bcb6c0f185be29b2a626d2f1430c110c823a7d by Miss Islington (bot) in branch '3.6':
bpo-35099: Update idlelib/help.html (GH-10353)
https://github.com/python/cpython/commit/54bcb6c0f185be29b2a626d2f1430c110c823a7d