Special Characters in extension keyboard shortcuts

[diminutivesloop]

When setting custom extension shortcuts via the "Manage Extension Shortcuts" menu item, it should be possible to use special characters such as "[". For example I've tried adding the shortcut "command + option + [" for switching between tab groups via the "Simple Tab Groups" extension which mirrors the built-in shortcut for switching between tabs. However when I try this I get the error message "Type a letter". Since built-in shortcuts contain special characters this limitation doesn't make sense.