24 Ranges library [ranges]

24.3 Range access [range.access]

24.3.1 ranges​::​begin [range.access.begin]

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