Proposed resolution:

This wording is relative to N4861.

1. Modify [range.semi.wrap] as indicated:

   -1- Many types in this subclause are specified in terms of an exposition-only class template semiregular-box. semiregular-box<T> behaves exactly like optional<T> with the following differences:

   1. (1.1) — […]

   2. (1.2) — […]

   3. (1.3) — If assignable_from<T&, const T&>copyable<T> is not modeled, the copy assignment operator is equivalent to:

      semiregular-box& operator=(const semiregular-box& that)
        noexcept(is_nothrow_copy_constructible_v<T>)
      {
        if (that) emplace(*that);
        else reset();
        return *this;
      }
      

   4. (1.4) — If assignable_from<T&, T>movable<T> is not modeled, the move assignment operator is equivalent to:

      semiregular-box& operator=(semiregular-box&& that)
        noexcept(is_nothrow_move_constructible_v<T>)
      {
        if (that) emplace(std::move(*that));
        else reset();
        return *this;
      }