[move.sent.ops]

constexpr move_sentinel();

Effects: Value-initializes last.

If is_trivially_default_constructible_v<S> is true, then this constructor is a constexpr constructor.

constexpr explicit move_sentinel(S s);

Effects: Initializes last with std::move(s).

template<class S2>
  requires convertible_to<const S2&, S>
    constexpr move_sentinel(const move_sentinel<S2>& s);

Effects: Initializes last with s.last.

template<class S2>
  requires assignable_from<S&, const S2&>
    constexpr move_sentinel& operator=(const move_sentinel<S2>& s);

Effects: Equivalent to: last = s.last; return *this;

constexpr S base() const;

Returns: last.

24 Iterators library [iterators]