Keyboard joystick emulation and KDB TOGGLE key

[MarioBross68]

Hello everyone ..., since mister help says that you can emulate the joystick with the keyboard ..., I have tried in all ways but I can't, does anyone know how the KDB TOGGLE key is defined?
The nes core hasn't implemented it yet or is it a bug?

I put here what it says in the help of mister:
Keyboard can be switched to joystick emulation. You need to define keys used for joystick emulation the same way you did for joysticks. Auto fire is also supported the same way as for joysticks. Button defined for “KBD TOGGLE” provides a quick switch between keyboard and joystick for defined keys

Thanks