In "Sliding" mode, if you pass it pageID = 5 and your delta is 2 it will return you 3 and 7. pageID of 6 would give you 4 and 8. In "Jumping" mode, if you pass it pageID = 1 and your perPage limit is 10, it will return you 1 and 10. PageID of 2 would give you 11 and 20.
if the method is called without parameter, pageID is set to currentPage