24 Ranges library [ranges]

24.7 Range adaptors [range.adaptors]

24.7.5 Transform view [range.transform]

24.7.5.5 views​::​transform [range.transform.adaptor]

The name views​::​transform denotes a range adaptor object ([range.adaptor.object]).
For some subexpressions E and F, the expression views​::​transform(E, F) is expression-equivalent to transform_­view{E, F}.