24 Ranges library [ranges]

24.6 Range factories [range.factories]

24.6.3 Iota view [range.iota]

24.6.3.5 views​::​iota [range.iota.adaptor]

The name views​::​iota denotes a customization point object ([customization.point.object]).
For some subexpressions E and F, the expressions views​::​iota(E) and views​::​iota(E, F) are expression-equivalent to iota_­view{E} and iota_­view{E, F}, respectively.