Test example:

1) Open IDLE (shell or editor)
2) Copy some text in the IDLE window
3) Close the IDLE window (instance should end)
4) Paste into application of choice
Without the patch, the clipboard is cleared when the instance ends so nothing is pasted. With the patch, the content remains in the clipboard as expected.

Note: This is not a problem if clipboard history is turned on or the content is pasted before closure, however the order of events above is fairly common for me.


Encoding:

In the latest commit to the pull, I have changed the encoding from UTF-8 to UTF-16 and my reasoning is as follows:

1) Most importantly, using UTF-8, characters with a unicode value >=2^8 are incorrectly copied as multiple characters. UTF-8 does support these characters but uses a different number of bytes per character (which is presumably what is causing these issues - for example, "AĀ" is encoded as "\x41\xc4\x80", which pastes as "A─Ç") UTF-16, however, correctly works for all characters supported by Tcl (see next point).

2) "Strings in Tcl are encoded using 16-bit Unicode characters" (https://www.tcl.tk/man/tcl8.2.3/TclCmd/encoding.htm). Therefore, the encoding we choose should have at least 16 bits allocated per character (meaning either UTF-16 or UTF-32).

3) Windows' "Unicode-enabled functions [...] use UTF-16 (wide character) encoding, which is [...] used for native Unicode encoding on Windows operating systems" (https://docs.microsoft.com/en-us/windows/win32/intl/unicode). For me, this was what decided the new encoding (between the two given in the previous point).