The ORKNavigablePageStep class is a concrete subclass of ORKPageStep  used for presenting a subgrouping of ORKStepViewController views using a UIPageViewController It allows for using an ORKOrderedTask as the model object used to define navigation  and has been added specifically to allow developers to use ORKNavigableOrderedTask and other subclasses of ORKOrderedTask with the ORKPageStep