Type Alias Literals<T>

Literals<T>: Extract<{
        [K in keyof T]: string extends K
            ? never
            : number extends K
                ? never
                : K
    } extends {
        [_ in keyof T]: infer U
    }
    ? U
    : never, string>

Extracts literally defined property names from a type T as a union of key name strings, minus any index signatures.