24 Ranges library [ranges]

24.3 Range access [range.access]

24.3.5 ranges​::​rbegin [range.access.rbegin]

The name ranges::rbegin denotes a customization point object.
The expression ranges::​rbegin(E) for some subexpression E is expression-equivalent to:
[Note
:
Whenever ranges::rbegin(E) is a valid expression, its type models Iterator.
end note
]