In clustered indexes on allpages-locked tables, leaf-level pages are also the data pages, and all rows are kept in physical order by the keys.
Physical ordering means that:
All entries on a data page are in index key order.
By following the “next page” pointers on the data pages, Adaptive Server reads the entire table in index key order.
On the root and intermediate pages, each entry points to a page on the next level.