The index step that moves to the next (later) chapter.
Compares the first and last chapter numbers: +1 when the array is ascending
(oldest-first), -1 when descending (newest-first). Falls back to +1
(assume oldest-first) when the direction is ambiguous.
The index step that moves to the next (later) chapter.
Compares the first and last chapter numbers:
+1when the array is ascending (oldest-first),-1when descending (newest-first). Falls back to+1(assume oldest-first) when the direction is ambiguous.