Type alias KeyPrefix<TStringMap>

KeyPrefix<TStringMap>: {
    [KeyPart in keyof TStringMap]: IsLastKeyPart<TStringMap[KeyPart]> extends string
        ? never
        : TStringMap[KeyPart] extends StringMap
            ? ToString<KeyPart> | `${ToString<KeyPart>}${KeyPartSeparator}${KeyPrefix<TStringMap[KeyPart]>}`
            : never
}[keyof TStringMap]

Union type of all key prefixes for TStringMap