It should also be noted that the frameStrata has to be at least DIALOG or higher for this to work.
Note that if you think you want to use this handler to take an in-game action based on a keypress, you probably really want to enable the
runOnUp attribute of a key binding, and check the
keystate variable and act accordingly. See HOWTO: Use Bindings.xml to create key bindings for your AddOn. This handler is more appropriate for cases where you want to allow freeform text entry and an EditBox isn't flexible enough.
arg1 - returned as a string representing the key that was released. For example, "W" or "A" or "S" or "D" (main keyboard keys) or "UP" or "LEFT" or "DOWN" or "RIGHT" (arrow keys) or "DELETE" or other extended keys or "SHIFT" or other modifier keys.