24 Ranges library [ranges]

24.7 Range adaptors [range.adaptors]

24.7.7 Take while view [range.take.while]

24.7.7.4 views​::​take_­while [range.take.while.adaptor]

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