26 Ranges library [ranges]

26.3 Range access [range.access]

26.3.9 ranges​::​crend [range.access.crend]

The name ranges​::​crend denotes a customization point object ([customization.point.object]).
Given a subexpression E with type T, let t be an lvalue that denotes the reified object for E.
  • If E is an rvalue and enable_borrowed_range<remove_cv_t<T>> is false, ranges​::​crend(E) is ill-formed.
  • Otherwise, let U be ranges​::​rend(possibly-const-range(t)).
    ranges​::​crend(E) is expression-equivalent to const_sentinel<decltype(U)>(U).
[Note 1: 
Whenever ranges​::​crend(E) is a valid expression, the types S and I of the expressions ranges​::​crend(E) and ranges​::​crbegin(E) model sentinel_for<S, I>.
If S models input_iterator, then S also models constant-iterator.
— end note]