Type Alias _U<T, U, $O>

_U: U extends `${any}`
    ? $ResolveBranch<$O, [$Else]>
    : U extends Uppercase<infer N>
        ? IsNotStringLiteral._D<N, $O>
        : U extends Lowercase<infer N>
            ? IsNotStringLiteral._D<N, $O>
            : $ResolveBranch<$O, [$Then], T>