27 Iterators library [iterators]

27.5 Iterator adaptors [predef.iterators]

27.5.1 Reverse iterators [reverse.iterators]

27.5.1.3 reverse_­iterator operations [reverse.iter.ops]

27.5.1.3.12 operator[] [reverse.iter.opindex]

constexpr unspecified operator[](difference_type n) const;