> 3 or more years ago, there was an issue about needing to define pairs like Control-Key-c and Control-Key-C in order to have crtl + c/C-key work the same regardless of the caps lock setting.  I also remember that the effect of Caps lock was system dependent.

Proposed scheme binds different actions on hotkeys with and without Shift: Ctrl-Z/Ctrl-Shift-Z, Ctrl-S/Ctrl-Shift-S. If don't touch CapsLock this is not an issue.

Yes, there is a problem with new buildin keys set in old IDLE versions. A lot of warnings is emitted on stderr. The solution for the "IDLE Dark" theme is not complete, since after adding next new theme we will encounter the same problem and should add options "name3", "name4"...

Updated patch uses the same solution for new keys set. But it also makes warnings be less annoying. Every warning is emitted just once, and only one warning is emitted for unknown keys set.