When instantiating `std::map` or `std::unordered_map`, the value type could be non-copyable (but movable). However, both class templates have copy ctors and assignments. I do not see any wording suggesting they shall be deleted like `std::optional` does ([optional.ctor] Remarks: This constructor is defined as deleted unless is_copy_constructible_v<T> is true. If is_trivially_copy_constructible_v<T> is true, this constructor is trivial.) Shall we refine the wording here?

Thanks,
Mingxin Wang