The mrdocs result type: polyfill::expected defaulting the error to Error.
Declared in <mrdocs/Support/Error/Expected.hpp>
template<
class T,
class E = Error>
using Expected = polyfill::expected<T, E>;
A thin alias over the standard-library std::expected polyfill that supplies the mrdocs Error type as the default error, so most code can write Expected<T>.