Add an option to force opposite shifts.

[Miodec]

• Use event.code to determine which side of the keyboard the key was pressed.
• Use event.location to determine which shift key was pressed
• Either ignore or allow that keypress if correct shift was pressed.
• Show a notice to the user that this will only work with layouts changed on the system level. Using programmable keyboards and changing the layout on the keyboard level (for example with QMK) will not work.

I just want to note that event.code is enough to determine which shift key has been pressed. It has ShiftRight and ShiftLeft values.

I also want to say that, neither event.code nor event.location can work out which shift was down if the event is not a shift, it would only tell you the code or location of the particular key that caused the event, and event.shiftKey wouldn't be the more informative. So I think you have to track RightShift and LeftShift key down and up events, and I think you know that already.

[Miodec]

Added

Thanks a ton! Can you also make this work as well for the symbols at the top and the right of the keyboard like ~!@#$% ,&*()-=and {}:">?? If so, you might want to keep ^ neutral as well.

Edit: Maybe I'll pull request, it seems easy enough:

1. Add the necessary symbols to the appropriate side lists
2. Edit the settings text.