Type Alias _U<T, U, $O>

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